WO2024057442A1

WO2024057442A1 - Transformer protection relay and transformer protection method

Info

Publication number: WO2024057442A1
Application number: PCT/JP2022/034406
Authority: WO
Inventors: 聡司竹村; 重遠尾田
Original assignee: 三菱電機株式会社
Priority date: 2022-09-14
Filing date: 2022-09-14
Publication date: 2024-03-21
Also published as: JPWO2024057442A1; JP7250230B1

Abstract

In a transformer protection relay (4), on the basis of whether or not both of a first condition (condition A) that second higher harmonic content percentage contained in a difference current between a primary side and a secondary side of one of phases is greater than a first set value (K1), and a second condition (condition B) that second higher harmonic content percentage contained in a difference current between a primary side and a secondary side of a corresponding phase is greater than a second set value (K2), are satisfied, a determining unit (75) for each phase locks output of a relay computing unit (64) of the corresponding phase. Here, the second set value (K2) is smaller than the first set value (K1).

Description

Transformer protection relay and transformer protection method

The present disclosure relates to a transformer protection relay and a transformer protection method.

In a transformer protection relay for a two-turn transformer, primary and secondary winding currents are detected by a current transformer (CT) connected to the primary and secondary windings. The transformer protection relay uses the detected primary and secondary winding currents to determine whether there is an internal failure based on the ratio differential principle.

When voltage is applied to a transformer, excitation inrush current (also referred to as inrush current) may occur. When an inrush current occurs, a difference occurs between the primary winding current and the secondary winding current, which causes malfunction of the transformer protection relay.

As a countermeasure against the above-mentioned malfunction, it is utilized that the excitation inrush current contains harmonics, especially second harmonics, in a proportion higher than a certain level with respect to the fundamental wave (rated frequency) component of the generator. Specifically, the ratio of the second harmonic component to the fundamental wave component included in the difference current between the primary winding current and the secondary winding current is calculated as the second harmonic content rate, and the second harmonic content is calculated as the second harmonic content rate. Differential relay operation is locked or inhibited when the rate is above a certain level.

However, the inrush current varies greatly depending on the hysteresis characteristics of the transformer core, residual magnetic flux, voltage application phase, etc. A phase that becomes smaller and smaller occurs. For this reason, in the method (hereinafter referred to as the second harmonic each phase determination method) that locks the ratio differential relay operation of only the phase whose second harmonic content is larger than the set value, the second harmonic content The transformer protection relay may malfunction in a phase where the ratio is smaller than that of other phases.

Therefore, a method (hereinafter referred to as the second harmonic three-phase OR determination method) is used that locks the ratio differential relay operation for all three phases if there is even one phase with a second harmonic content rate higher than the set value. There may be cases where According to this method, the occurrence of inrush current can be detected with high reliability.

In addition, Japanese Patent Application Laid-open No. 01-259720 (Patent Document 1) discloses that when the second harmonic content rate in any two of the three phases becomes larger than the set value, a ratio differential relay is activated for all three phases. (hereinafter referred to as the second harmonic two-phase AND determination method) is disclosed. In this document, a second harmonic two-phase AND determination method is proposed as a complement to the conventional second harmonic each phase determination method.

Note that Japanese Patent No. 6840306 (Patent Document 2) discloses that when determining the occurrence of inrush current, a set value for comparison with the second harmonic content rate is updated in accordance with changes in transformer characteristics over time. Disclose.

Japanese Patent Application Publication No. 01-259720 Patent No. 6840306

The transformer protection relay using the second harmonic three-phase OR determination method described above has a problem in that the relay cannot operate if a transformer failure occurs while an inrush current is being generated. Normally, when the transformer is Y-connected, the detected value of the three-phase CT is converted into a line current when the transformer is Δ-connected. Therefore, in the case of a one-phase fault in a transformer, the fault current is included in the line current for two phases after conversion. Since most of the fault current is the fundamental wave component, the second harmonic component is hardly detected for the two phases where the fault current is detected, but the second harmonic component is not detected for the one phase where the fault current is not detected. continues. As a result, in the transformer protection relay using the second harmonic three-phase OR determination method, the relay operation continues to be locked even if a one-phase failure of the transformer occurs while the magnetizing inrush current is being generated.

On the other hand, in the above-mentioned transformer protection relay using the second harmonic two-phase AND judgment method, if a transformer failure occurs while an inrush current is generated, the second harmonic content rate of any two phases decreases. do. Therefore, there is an advantage that the lock is reliably released and the ratio differential relay can operate.

However, the transformer protection relay using the second harmonic two-phase AND determination method may not be able to detect the occurrence of inrush current. Generally, the second harmonic content of the inrush current is relatively large for one phase, but relatively small for the other two phases. In a normal case, since the second harmonic content of any two phases exceeds the general setting value of 15%, inrush current can be detected. However, in some cases, due to the effects of the transformer's saturation voltage and residual magnetic flux, the second harmonic content of any one phase exceeds 15%, but the second harmonic content of the other two phases exceeds 15%. It may be lower than that. In that case, the transformer protection relay using the second harmonic two-phase AND determination method cannot prevent malfunctions caused by the magnetizing inrush current.

Furthermore, it is difficult to set the above setting value to less than 10%. If the power system in which the transformer is installed uses transmission lines with large capacitance components, such as power cables, in the event of a failure, the reactor component of the transformer winding and the ground capacitance of the transmission line Harmonics are generated because the components resonate. In this case, if the length of the power cable is relatively long, the resonance frequency approaches the second harmonic, and the second harmonic content increases to nearly 10%. For this reason, it is difficult to set the above setting value to less than 10%, and it is generally set within the range of 10% to 15%, and among these, it is often set to 15%.

The present disclosure has been made in consideration of the above problems, and one of its purposes is to reliably detect the occurrence of inrush current and lock the relay output, and to To provide a transformer protection relay that releases the lock and performs relay operation when a transformer failure occurs. Other objects and features of the present disclosure will be described in the embodiments below.

The transformer protection relay of one embodiment includes a first relay calculation section, a second relay calculation section, a third relay calculation section, a first determination section, a second determination section, and a third determination section. It is equipped with a section. The first relay calculation section, the second relay calculation section, and the third relay calculation section are provided corresponding to the first phase, second phase, and third phase of the transformer, respectively, and are Current differential relay calculation is performed based on the fundamental wave component included in the difference current between the primary and secondary sides of the transformer. The first determination section, the second determination section, and the third determination section are provided corresponding to the first phase, second phase, and third phase of the transformer, respectively, and detect the occurrence of inrush current. Make a judgment to Each of the first determining section, the second determining section, and the third determining section has a difference current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase. The first condition is that the content rate of the second harmonic included in is larger than the first set value, and the content rate of the second harmonic included in the difference current between the primary side and the secondary side of the corresponding phase is the first condition. It is determined whether or not the second condition, which is greater than the set value of 2, is met. The second set value is smaller than the first set value. Each of the first determining section, the second determining section, and the third determining section determines the output of the relay calculating section of the corresponding phase based on whether the first condition and the second condition are both satisfied. lock.

According to the above embodiment, the determination unit for each phase of the transformer protection relay has a first setting that the content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one phase is The first condition that the value is larger than the second set value and the second condition that the content rate of the second harmonic included in the difference current between the primary side and the secondary side of the corresponding phase are larger than the second set value are both satisfied. The output of the corresponding relay calculation section is locked based on whether or not the relay is activated. This enables a transformer protection relay to reliably detect the occurrence of inrush current and lock the relay output, as well as to release the lock and operate the relay in the event of a transformer failure while inrush current is occurring. Can be provided.

FIG. 3 is a diagram for explaining the connection between a transformer and its protection relay. FIG. 2 is a block diagram showing an example of the hardware configuration of the transformer protection relay in FIG. 1. FIG. FIG. 2 is a block diagram for explaining signal processing in an arithmetic processing section. FIG. 4 is a block diagram showing an example of the functional configuration of the A-phase calculation section in FIG. 3. FIG. FIG. 3 is a diagram summarizing the characteristics of individual determination conditions for inrush current generation in a table format. FIG. 4 is a block diagram showing a specific example of the configuration of an inrush determination section included in the A-phase calculation section of FIG. 3. FIG. FIG. 7 is a timing diagram illustrating the operation of the in-rush determination section of FIG. 6. FIG. 4 is a block diagram illustrating a specific configuration example of an inrush determination section included in the A-phase calculation section of FIG. 3 in the transformer protection relay of Embodiment 2. FIG. FIG. 9 is a timing diagram illustrating the operation of the in-rush determination section of FIG. 8; FIG. 9 is a block diagram showing a modification of the inrush determination section of FIG. 8; 4 is a block diagram illustrating a specific configuration example of an inrush determination section included in the A-phase calculation section of FIG. 3 in the transformer protection relay of Embodiment 3. FIG. FIG. 12 is a timing diagram illustrating the operation of the in-rush determination section of FIG. 11. FIG. FIG. 12 is a block diagram showing a modification of the inrush determination section of FIG. 11; 4 is a block diagram illustrating a specific configuration example of an inrush determination section included in the A-phase calculation section of FIG. 3 in the transformer protection relay of Embodiment 4. FIG. FIG. 15 is a timing diagram illustrating the operation of the in-rush determination section of FIG. 14; FIG. 15 is a block diagram showing a modification of the inrush determination section of FIG. 14; 4 is a block diagram showing a specific configuration example of an inrush determination section included in the A-phase calculation section of FIG. 3 in the transformer protection relay of Embodiment 5. FIG. FIG. 18 is a timing diagram illustrating the operation of the in-rush determination section of FIG. 17; FIG. 12 is a block diagram showing an example of a functional configuration of an A-phase calculation unit in the calculation processing unit in the transformer protection relay of Embodiment 6. FIG. 7 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 0°. FIG. 20A is an enlarged view of a portion from 0.089 seconds to 0.091 seconds in FIG. 20A. FIG. 7 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 30°. FIG. 21A is an enlarged view of a portion from 0.0875 seconds to 0.0895 seconds in FIG. 21A. FIG. 7 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 60°. It is an enlarged view of the part from 0.082 seconds to 0.084 seconds of FIG. 22A. FIG. 7 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 120°. FIG. 23A is an enlarged view of a portion from 0.084 seconds to 0.086 seconds in FIG. 23A.

Hereinafter, each embodiment will be described in detail with reference to the drawings. In addition, the same reference numerals are given to the same or corresponding parts, and the description thereof will not be repeated.

Embodiment 1.
[Connection between transformer and protective relay]
FIG. 1 is a diagram for explaining the connection between a transformer and its protection relay. A three-phase transformer 1 shown in FIG. 1 is a YΔ transformer including a Y-connected primary winding 2 and a Δ-connected secondary winding 3. Note that the three-phase transformer 1 is not limited to the YΔ transformer, but may be other types of transformers such as a YY transformer or a ΔΔ transformer.

The three-

phase lines

5A, 5B, and 5C on the primary side connected to the primary winding 2 of the three-phase transformer 1 are provided with current transformers CT1A, CT1B, and CT1C, respectively (hereinafter collectively referred to as current transformer CT1). is provided. Current transformer CT1A detects current I1A flowing through A-phase line 5A, current transformer CT1B detects current I1B flowing through B-phase line 5B, and current transformer CT1C detects current I1C flowing through C-phase line 5C. Detect. The first end of each current transformer CT1 is connected to a common ground pole GND, and the second end of each current transformer CT1 is connected to the input transformer (11 in FIG. 2) of the corresponding channel of the transformer protection relay 4. connected to the primary side of the That is, current transformers CT1A, CT1B, and CT1C are Y-connected.

Similarly, three-

phase lines

6A, 6B, and 6C on the secondary side connected to the secondary winding 3 of the three-phase transformer 1 are connected to current transformers CT2A, CT2B, and CT2C (current transformers CT2A, CT2B, and CT2C, respectively). CT2) is provided. Current transformer CT2A detects current I2A flowing through A-phase line 6A, current transformer CT2B detects current I2B flowing through B-phase line 6B, and current transformer CT2C detects current I2C flowing through C-phase line 6C. Detect. The first end of each current transformer CT2 is connected to a common ground pole GND, and the second end of each current transformer CT2 is connected to the input transformer (11 in FIG. 2) of the corresponding channel of the transformer protection relay 4. connected to the primary side of the That is, current transformers CT2A, CT2B, and CT2C are Y-connected.

[Hardware configuration example of transformer protection relay]
FIG. 2 is a block diagram showing an example of the hardware configuration of the transformer protection relay 4 of FIG. 1. As shown in FIG. Referring to FIG. 2, transformer protection relay 4 has a configuration similar to that of a so-called digital relay. Specifically, the transformer protection relay 4 includes an input conversion section 10, an A/D conversion section 20, an arithmetic processing section 30, and an I/O (Input and Output) section 40.

The input conversion unit 10 includes auxiliary transformers 11_1, 11_2, . . . for each input channel. The input conversion unit 10 receives signals representing primary side currents I1A, I1B, and I1C output from current transformers CT1A, CT1B, and CT1C, respectively, and secondary side currents output from current transformers CT2A, CT2B, and CT2C, respectively. Signals representing currents I2A, I2B, and I2C are individually taken in through six auxiliary transformers 11. Each auxiliary transformer 11 converts these input signals into signals at a voltage level suitable for signal processing in the A/D conversion section 20 and the arithmetic processing section 30.

The A/D conversion unit 20 includes analog filters (AF) 21_1, 21_2, ..., sample hold circuits (S/H) 22_1, 22_2, ..., and a multiplexer (MPX) 23. , and an A/D converter 24. Analog filter 21 and sample hold circuit 22 are provided for each channel of input conversion section 10.

Each analog filter 21 is a low-pass filter or a band-pass filter provided to remove aliasing errors during A/D conversion. Each sample and hold circuit 22 samples and holds the signal that has passed through the corresponding analog filter 21 at a specified sampling frequency. The multiplexer 23 sequentially selects the voltage signals held in the sample and hold circuits 22_1, 22_2, . A/D converter 24 converts the signal selected by multiplexer 23 into a digital value.

The arithmetic processing unit 30 includes a CPU (Central Processing Unit) 31, a RAM (Random Access Memory) 32, a ROM (Read Only Memory) 33, and a bus 34 connecting these. The CPU 31 controls the overall operation of the transformer protection relay 4 by operating according to a program. RAM32 and ROM33 are used as main memory of CPU31. By using an electrically rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable ROM) and a flash memory as a storage medium of the ROM 33, programs, setting values for signal processing, etc. can be stored.

The I/O section 40 includes a digital input (D/I) circuit 41 and a digital output (D/O) circuit 42. The digital input circuit 41 and the digital output circuit 42 are interface circuits for inputting and outputting digital signals between the CPU 31 and an external device. For example, the digital output circuit 42 outputs a trip signal to a related circuit breaker according to a command from the CPU 31.

Note that at least a part of the functions of the arithmetic processing unit 30 may be realized as an electronic circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or one of the CPU, ASIC, and FPGA. It may be realized by combining two or more.

[Signal processing in the arithmetic processing unit]
FIG. 3 is a block diagram for explaining signal processing in the arithmetic processing section. Referring to FIG. 3, the calculation processing unit 30 functionally includes Y/

Δ conversion units

50 and 51,

gain adjustment units

52 and 53, an A phase calculation unit 54, a B phase calculation unit 55, and a C and a phase calculation section 56.

The Y/

Δ converters

50 and 51 convert the line current of the Y connection into the line current of the Δ connection. Hereinafter, the case where the Yd1 wiring method of the YΔ transformer as shown in FIG. 1 will be explained. In this case, the primary winding 2 is a Y winding, and the secondary winding 3 is a Δ winding. The phases of the line currents I2A, I2B, and I2C detected by the current transformer CT2 on the secondary side are delayed by 30° (corresponding to the 1 o'clock direction). Therefore, by converting the line currents I1A, I1B, and I1C of the Y connection on the primary side into the line currents I'1A, I'1B, and I'1C of the Δ connection, the phases of the two are matched. Specifically, the primary side line currents I'1A, I'1B, and I'1C after conversion are as follows:
I'1A=1IA-I1C...(1A)
I'1B=I1B-I1A...(1B)
I'1C=I1C-I1B...(1C)
It is expressed as

Since the secondary winding 3 of the transformer 1 in the case of FIG. 1 is a Δ winding, the Y/Δ conversion unit 51 is mounted, but no Y/Δ conversion processing is performed. Therefore, I'2A=I2A, I'2B=I2B, and I'2C=I2C. In FIG. 3, the Y/Δ conversion unit 51 is shown with a broken line to indicate that Y/Δ conversion processing is not performed.

Note that in the case of a YY transformer, Y/Δ conversion is performed on both the primary and secondary sides in order to cancel the zero-sequence current in the case of an external ground fault. In the case of a ΔΔ transformer, no Y/Δ conversion is performed on either the primary or secondary side.

Also, instead of the Y/Δ conversion according to the above calculation, the primary side current transformers CT1A, CT1B, CT1C may be connected in a Δ manner so that the primary and secondary sides of the transformer 1 are in phase. . Thereby, the phase of the current detected by the primary-side current transformer CT1 and the phase of the detected current by the secondary-side current transformer CT2 can be aligned.

The gain adjustment unit 52 calculates the final primary currents I'1A, I'1B, and I'1C by multiplying the Y/Δ-converted primary current by a constant M1. Similarly, the gain adjustment unit 53 calculates the final secondary currents I'2A, I'2B, and I'2C by multiplying the secondary current by a constant M2. Constants M1 and M2 are determined by adjusting the transformation ratio of the three-phase transformer 1 and the primary and secondary sides so that the fundamental wave component of the primary current and the fundamental wave component of the secondary current cancel in the case of an external fault. It is determined in advance according to the CT ratio of current transformers CT1 and CT2.

The A-phase calculation unit 54 uses the A-phase primary current I'1A and the A-phase secondary current I'2A to perform current differential relay calculation using the ratio differential method and inrush current for the A-phase. The presence/absence is determined. Similarly, the B-phase calculation unit 55 performs a current differential relay calculation using the ratio differential method for the B-phase using the B-phase primary current I'1B and the B-phase secondary current I'2B. The presence or absence of rush current is determined. The C-phase calculation unit 56 uses the C-phase primary current I'1C and the C-phase secondary current I'2C to perform current differential relay calculation using the ratio differential method and inrush current for the C-phase. The presence/absence is determined. Since the A-phase calculation unit 54, the B-phase calculation unit 55, and the C-phase calculation unit 56 have similar configurations, the configuration of the A-phase calculation unit 54 will be described below as a representative.

FIG. 4 is a block diagram showing an example of the functional configuration of the A-phase calculation section 54 in FIG. 3. Referring to FIG. 4, A-phase calculation unit 54 includes

filters

60, 61, 66, 67, 68, differential current calculation unit 62, suppression current calculation unit 63, ratio differential relay calculation unit 64, and harmonic It includes a wave difference current calculation unit 65, effective

value calculation units

69, 70, 71, content

rate calculation units

72, 73, 74, an inrush determination unit 75, and an AND calculation unit 76.

The filter 60 receives input of time series data of the A-phase primary current I'1A, passes the fundamental wave component (1f) of the power system, and filters out the DC component, the second harmonic component (2f), and the third harmonic component. It is configured as a bandpass filter that suppresses other components such as a wave component (3f) and a fourth harmonic component (4f). Similarly, the filter 61 is configured as a bandpass filter that receives the A-phase secondary current I'2A, passes the fundamental wave component (1f) of the power system, and suppresses other components.

The difference current calculation unit 62 calculates the time series data of the fundamental wave component I'1A _1f of the A-phase primary current that has passed through the filter 60 and the fundamental wave component I'2A _1f of the A-phase secondary current that has passed through the filter 61. calculate the effective value of the sum (i.e., vector sum) with the time series data. Here, by reversing the polarity of the primary current transformer CT1 and the secondary current transformer CT2, the difference current calculation unit 62 can calculate the difference between the fundamental wave component of the primary current and the secondary current. The effective value of the difference from the fundamental wave component is calculated as the difference current IdA _1f . That is, if |E| represents the effective value of the quantity of electricity E, the difference current IdA _1f is
IdA _1f = | I'1A _1f + I'2A _1f | ...(2)
It is expressed as Note that although the present disclosure will be described using effective values, all effective values may be changed to amplitude values. In this case, |E| represents the amplitude value of the electrical quantity E.

The suppression current calculation unit 63 calculates the effective value of the fundamental wave component I'1A _1f of the A-phase primary current that has passed through the filter 60 and the fundamental wave component I'2A _1f of the A-phase secondary current that has passed through the filter 61. The scalar sum with the effective value is calculated as the suppression current IrA _1f . That is, the suppression current IrA _1f is
IrA _1f = | I'1A _1f | + | I'2A _1f | ...(3)
It is expressed as

The ratio differential relay calculation unit 64 uses the difference current IdA _1f and the suppression current IrA _1f to determine whether an internal failure has occurred in the A-phase winding of the three-phase transformer 1. Specifically, the ratio differential relay calculation unit 64 sets ratio setting values as C1 and C1', and sets minimum setting values as C2 and C2'.
IdA _1f ≧C1×Ird _1f +C2…(4A)
IdA _1f ≧C1'×Ird _1f +C2'...(4B)
If both are satisfied, it is determined that there is an internal failure. The ratio differential relay calculation unit 64 outputs a relay operation signal for opening an external circuit breaker or the like when it is determined that there is an internal failure.

The harmonic difference current calculation unit 65 calculates the sum (i.e., vector sum) of the time series data of the A-phase primary current I'1A and the time series data of the A-phase secondary current for extraction of harmonic components. It is calculated as the difference current IdA. That is, the difference current IdA is
IdA=I'1A+I'2A...(5)
It is expressed as

The filter 66 receives input of time series data of the difference current IdA, passes the second harmonic component (2f), and passes through the DC component, fundamental wave component (1f), third harmonic component (3f), and fourth harmonic component. It is configured as a bandpass filter that suppresses other components such as the wave component (4f).

Similarly, the filter 67 receives input of time-series data of the difference current IdA, passes the third harmonic component (3f), and passes the DC component, fundamental component (1f), second harmonic component (2f), It is configured as a bandpass filter that suppresses other components such as the fourth harmonic component (4f).

Further, the filter 68 receives input of time series data of the difference current IdA, passes the fourth harmonic component (4f), direct current component, fundamental wave component (1f), second harmonic component (2f), and the fourth harmonic component (4f). It is configured as a bandpass filter that suppresses other components such as the third harmonic component (3f).

Note that the filter calculations by the filters 66 to 68 are first performed on the time series data of the A-phase primary current I'1A and the time series data of the A-phase secondary current I'2A, and then the harmonic components are The vector sum of the A-phase primary current and the A-phase secondary current may be calculated by the difference current calculation unit 65 for each time.

The effective value calculation unit 69 calculates the effective value IdA _2f of the second harmonic component of the difference current that has passed through the filter 66. Similarly, the effective value calculation unit 70 calculates the effective value IdA _3f of the third harmonic component of the difference current that has passed through the filter 67. The effective value calculation section 71 calculates the effective value IdA _4f of the fourth harmonic component of the difference current that has passed through the filter 68.

The content calculation unit 72 calculates the effective value IdA 1f of the fundamental wave component of the A-phase difference current calculated by the difference current calculation unit 62 and the effective value IdA _1f of the second harmonic component of the A-phase difference current calculated by the effective value calculation unit 69. Receives input of value IdA _2f . Then, the content calculation unit 72 calculates the ratio IdA _{2f /IdA 1f} _of the effective value IdA _2f of the second harmonic component of the A phase difference current to the effective value IdA _1f of the fundamental wave component of the A phase difference current. Calculate as a percentage.

Similarly, the content calculation unit 73 calculates the effective value IdA _1f of the fundamental wave component of the A phase difference current calculated by the difference current calculation unit 62 and the third harmonic of the A phase difference current calculated by the effective value calculation unit 70. An input of the effective value IdA _3f of the component is received. Then, the content calculation unit 73 calculates the ratio IdA _{3f /IdA 1f} _of the effective value IdA _3f of the third harmonic component of the A phase difference current to the effective value IdA _1f of the fundamental wave component of the A phase difference current. Calculate as a percentage.

The content calculation unit 74 calculates the effective value IdA _1f of the fundamental wave component of the A-phase difference current calculated by the difference current calculation unit 62 and the effective value IdA 1f of the fourth harmonic component of the A-phase difference current calculated by the effective value calculation unit 71. Receives input of value IdA _4f . Then, the content calculation unit 74 calculates the ratio IdA _4f /IdA _1f of the effective value IdA _4f of the fourth harmonic component of the A phase difference current to the effective value IdA _1f of the fundamental wave component of the A phase difference current, Calculate as a percentage.

The inrush determination unit 75 determines at least the second harmonic content rate of the harmonic content rate of the A phase, which is the own phase, calculated by the content rate calculation units 72 to 74, and the second harmonic content rate of the other two phases. It is determined whether or not an inrush current is occurring in the A phase, which is the own phase. When the inrush determination unit 75 determines that an inrush current is generated, it activates a lock signal for locking the relay output. A specific method for determining whether an inrush current is generated will be described later with reference to FIGS. 5 to 18.

The AND operator 76 calculates the logical product of the relay operation signal output from the ratio differential relay operation unit 64 and the inverted signal of the lock signal output from the inrush determination unit 75. Therefore, when the lock signal is in the active state, the output of the AND operator 76 becomes inactive, and the relay output is locked.

In the case of the B-phase calculation section 55, the A phase may be changed to the B phase in the above description, and in the case of the C phase calculation section 56, the A phase may be changed to the C phase in the above description. good. Therefore, detailed explanation will not be repeated.

[Judgment conditions for inrush current generation]
Next, conditions for determining the occurrence of inrush current will be explained. In the present disclosure, by combining a plurality of determination conditions, the reliability of determining the occurrence of inrush current is improved, and the occurrence of inrush current is not detected when an internal failure of the transformer occurs.

FIG. 5 is a diagram summarizing the characteristics of individual determination conditions for inrush current generation used in the present disclosure in a table format. The characteristics of the determination conditions A to F will be explained below with reference to FIG.

Judgment condition A is the condition that the second harmonic content included in the difference current between the primary side and the secondary side is larger than the set value K1 in one of the three phases (i.e., the second harmonic three-phase OR judgment method). ). The set value K1 is set to a value larger than the maximum value of the second harmonic content rate that occurs due to an internal failure of the transformer. For example, K1=15%.

Since the second harmonic content of any one of the three phases becomes considerably large when an inrush current is generated, according to determination condition A, the occurrence of an inrush current can be reliably detected. Further, if a one-phase failure occurs inside the transformer while an inrush current is generated, the second harmonic is not detected in the failure phase because the failure current has a small amount of second harmonic. However, since inrush current is included in phases that are not faulty phases, there is a possibility that detection of inrush current will continue.

Judgment condition B is an individual judgment condition for each phase of the transformer, and is a condition that the second harmonic content included in the difference current between the primary side and the secondary side of the own phase is greater than the set value K2 (i.e. , second harmonic phase determination method). The set value K2 is set to a value that can be detected even when the content rate of the second harmonic included in the inrush current is the minimum. For example, K2=5%.

According to determination condition B, the set value K2 is set to a value smaller than when the content rate of the second harmonic included in the inrush current is the minimum, so the occurrence of the inrush current can be reliably detected. However, for two of the three phases, the second harmonic content rate may temporarily become less than the set value K2. In this case, in-rush current temporarily becomes undetectable for a phase in which the second harmonic content rate temporarily decreases. In addition, if a one-phase failure occurs inside the transformer during the generation of inrush current, if the transformer is connected to a power transmission line with a large ground capacitance, such as a relatively long power cable, The ground capacitance component of the power transmission line and the inductive component of the transformer winding may cause a resonance phenomenon with a resonant frequency close to the second harmonic. Therefore, there is a possibility that a second harmonic due to this resonance phenomenon will be detected in the fault current. However, this resonance decays within a few cycles, so the second harmonic becomes undetectable after a while. When the transformer is connected to a power transmission line with a small ground capacitance, the fault current contains almost no harmonics, so the second harmonic becomes undetectable immediately after the fault occurs.

Judgment condition C is an individual judgment condition for each phase of the transformer, and is a judgment condition for the second harmonic, third harmonic, and fourth harmonic included in the difference current between the primary side and the secondary side of the own phase. The condition is that the sum of each content rate is greater than the set value K3. The set value K3 is set to a value smaller than the sum of the respective content rates of the second harmonic, the third harmonic, and the fourth harmonic included in the inrush current. For example, K3=15%.

According to determination condition C, the set value K3 is set to a value smaller than the sum of the content rates of each of the second harmonic, third harmonic, and fourth harmonic included in the inrush current. The occurrence of inrush current can be detected reliably. There is an advantage that the temporary drop in the second harmonic can be compensated for by the third harmonic and the fourth harmonic. In addition, if a one-phase failure occurs inside a transformer during the generation of inrush current, and the transformer is connected to a power cable, resonance will occur due to the capacitance component of the power cable and the inductive component of the transformer. Because of this, there is a possibility that the fault current contains harmonics and that these harmonics are detected. However, this resonance decays within a few cycles and the harmonics become undetectable. If the fault current contains almost no harmonics because the transformer is connected to an overhead line, the harmonics will go undetected immediately after the fault occurs.

Judgment condition D is the condition that the second harmonic content included in the difference current between the primary side and the secondary side in any two of the three phases is both greater than the set value K1 (that is, the second harmonic content rate of the second harmonic 2 (phase AND judgment method). The set value K1 is set to the same value as in the case of determination condition A, for example, 15%.

In the case of determination condition D, there may be a case where the second harmonic content rate is larger than the above set value K1 in only one of the three phases. Therefore, although it is possible to detect the occurrence of inrush current in most cases, it cannot be said that it can be detected reliably. In addition, normally, when the transformer is Y-connected, the detected value of the three-phase CT is converted to the line current when it is Δ-connected, so even in the case of a one-phase failure of the transformer, the fault current is transferred to the transformer. Detected on two phases of the device. Therefore, if a one-phase failure occurs inside the transformer while an inrush current is being generated, the inrush current will definitely not be detected.

Judgment condition E is an individual judgment condition for each phase of the transformer, and is the sum of the contents of the second harmonic and fourth harmonic included in the difference current between the primary side and the secondary side of the own phase. is larger than the set value K4. The set value K4 is set to a value that can be detected even when the content rate of each of the second harmonic and the fourth harmonic included in the inrush current is the minimum. For example, K4=6%.

According to the determination condition E, the set value K4 is set to a value smaller than the sum of the respective content rates of the second harmonic and the fourth harmonic included in the inrush current, so that the generation of the inrush current is prevented. Can be detected reliably. There is an advantage that the temporary drop in the second harmonic can be compensated for by the fourth harmonic. In addition, if a one-phase failure occurs inside the transformer during the generation of inrush current, if the transformer is connected to a power transmission line with a large ground capacitance, such as a relatively long power cable, The ground capacitance component of the power transmission line and the inductive component of the transformer winding may cause a resonance phenomenon with a resonant frequency close to the second harmonic. Therefore, there is a possibility that a second harmonic due to this resonance phenomenon will be detected in the fault current. However, this resonance decays within a few cycles and the harmonics become undetectable. If the transformer is connected to a power transmission line with low ground capacitance, the fault current will contain almost no harmonics, so harmonics will go undetected immediately after a fault occurs.

Judgment condition F is obtained by changing the setting value K1 of judgment condition D to K2. That is, the determination condition F is a condition that the second harmonic content included in the difference current between the primary side and the secondary side in any two of the three phases is both larger than the set value K2. The set value K2 is set to a value that can be detected even when the content rate of the second harmonic included in the inrush current is the minimum. For example, K2=5%.

According to the determination condition F, the set value K2 is set to a value smaller than that when the content rate of the second harmonic included in the inrush current is the minimum, so the occurrence of the inrush current can be reliably detected. However, for two of the three phases, the second harmonic content rate may temporarily become less than the set value K2. In addition, normally, when the transformer is Y-connected, the detected value of the three-phase CT is converted to the line current when it is Δ-connected, so even if the transformer has a one-phase failure, the fault current is transferred to the transformer. Detected on two phases of the device. Therefore, if a one-phase failure occurs inside the transformer while an in-rush current is being generated, the in-rush current will definitely not be detected under the determination condition F.

[Specific configuration of in-rush determination section]
FIG. 6 is a block diagram showing a specific example of the configuration of the inrush determining section 75 included in the A-phase calculating section 54 of FIG. 3. In FIG. The determination conditions of the in-rush determination section 75 in FIG. 6 are a combination of the aforementioned determination conditions A and B.

In addition, in the following description, the second harmonic content rate IdA _2f /IdA _1f of the A phase is also expressed as (2f/1f)A. The third harmonic content rate IdA _3f /IdA _1f of the A phase is also expressed as (3f/1f)A. The fourth harmonic content rate IdA _4f /IdA _1f of the A phase is also expressed as (4f/1f)A. The same applies to the B phase and C phase.

As shown in FIG. 6, the in-rush determination unit 75 includes

determination units

80, 81, 82, and 83, an OR operator 84, and an AND operator 85.

The determining unit 80 determines whether the second harmonic content rate (2f/1f) A of the A phase is larger than the set value K1. The determination unit 81 determines whether the second harmonic content rate (2f/1f)B of the B phase is larger than the set value K1. The determination unit 82 determines whether the second harmonic content rate (2f/1f) C of the C phase is larger than the set value K1. As mentioned above, the set value K1 is, for example, 15%, which is a relatively large value.

The OR calculator 84 performs an OR operation on the determination results of the

determination units

80, 81, and 82. Therefore, the output of the OR calculator 84 indicates that the content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the A, B, and C phases is lower than the set value K1. This indicates whether or not the determination condition A that the value is large is satisfied.

In the case of the A-phase calculation unit 54, the determination unit 83 determines whether the second harmonic content (2f/1f)A of the A-phase, which is the own phase, is greater than the set value K2. As mentioned above, the set value K2 is, for example, 5%, which is significantly smaller than the set value K1.

Note that in the case of the inrush determination unit 75 included in the B-phase calculation unit 55 in FIG. It is determined whether it is larger than K2. In addition, in the case of the inrush determination unit 75 included in the C-phase calculation unit 56 in FIG. Determine whether or not. Therefore, for each phase of the three-phase transformer 1, it is determined whether or not the determination condition B that the content rate of the second harmonic included in the difference current between the primary side and the secondary side is greater than the set value K2 is met. That will happen.

The AND operator 85 performs an AND operation between the output of the OR operator 84 and the output of the determination unit 83. When the lock signal output from the AND operator 85 is in the active state, the relay output of the corresponding phase (A phase in the case of FIG. 6) is locked, and when the lock signal is inactive, the relay output of the corresponding phase ( A phase) relay output is not locked. The same applies to the B-phase and C-phase, so if there is a phase for which the determination condition A is satisfied and the determination condition B is also satisfied, the protection relay output of that phase will be locked.

According to the configuration of the inrush determination section 75 described above, when an inrush current occurs, the second harmonic content rate of one phase among the three phases is always greater than the set value K1, and the second harmonic content rate of the remaining phases is always greater than the set value K1. Since the harmonic content rate is normally greater than the set value K2, the occurrence of inrush current can be detected. Further, when an internal failure occurs in the three-phase transformer 1, the second harmonic content rate decreases in the phase where the detected current value includes the fault current, since the fault current is mainly composed of the fundamental wave component. Therefore, even if the set value K2 is set to a value considerably lower than the set value K1, the occurrence of inrush current will not be detected in a phase where the detected current value includes a fault current.

FIG. 7 is a timing diagram illustrating the operation of the in-rush determination unit 75 of FIG. 6. The portion indicated by the thick line in FIG. 7 indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 7, power is applied to three-phase transformer 1 at time t1. Due to the generation of inrush current, the second harmonic content rate (2f/1f) A of the A phase and the second harmonic content rate (2f/1f) C of the C phase both exceed the set value K2 at time t2. , the determination condition B is satisfied for the A phase and the C phase. Further, at time t3, the second harmonic content rate (2f/1f)B of the B phase exceeds the set value K1, so the determination condition A is satisfied. Although not shown in FIG. 7, the second harmonic content rate (2f/1f) B of the B phase naturally exceeds the set value K2 at a time point before time t3. Therefore, at time t3, lock signals for locking the relay outputs in each of the A, B, and C phases become active.

In the example of FIG. 7, among the difference currents of the A phase, B phase, and C phase through which inrush current flows, the phase with the smallest second harmonic content is the C phase. The second harmonic content rate (2f/1f) C of the C phase exceeds the set value K2 at time t2, but does not exceed the set value K1. The phase with the next lowest second harmonic content is the A phase. The second harmonic content rate (2f/1f) A of the A phase exceeds the set value K1 at time t4, but does not exceed the set value K1 continuously and returns temporarily on the way. In FIG. 7, the broken line indicates that the set value K1 is not continuously exceeded.

At time t8, a failure occurs in the A phase inside the transformer. As a result, a fault current flows through the A phase, so that the second harmonic content rate (2f/1f) A of the A phase decreases and becomes equal to or less than the set value K2 at time t9. As a result, the A-phase lock signal becomes inactive, and the A-phase relay output is unlocked.

[Effects of Embodiment 1]
As described above, the transformer protection relay (4) of the first embodiment includes a first relay calculation section (64 of the A-phase calculation section 54), a second relay calculation section (64 of the B-phase calculation section 55), and a third relay calculation section (64 of the C-phase calculation section 56), a first judgment section (75 of the A-phase calculation section 54), a second judgment section (75 of the B-phase calculation section 55), and a third relay calculation section (64 of the C-phase calculation section 56). 3 determination units (75 of the C phase calculation unit 56).

The first relay calculation section, the second relay calculation section, and the third relay calculation section (64) are connected to the first phase (A phase), the second phase (B phase), and the second phase (B phase) of the transformer (1). It is provided corresponding to each of the three phases (C phase), and performs current differential relay calculation based on the fundamental wave component included in the difference current between the primary side and the secondary side of the transformer of the corresponding phase. The first determining section, the second determining section, and the third determining section (75) determine the first phase (A phase), the second phase (B phase), and the third phase ( C phase), and performs judgment to detect the occurrence of inrush current.

Specifically, each of the first determining section, the second determining section, and the third determining section (75) is connected to the primary side of any one of the first phase, the second phase, and the third phase. The first condition (condition A) that the content rate of the second harmonic included in the differential current with the secondary side is greater than the first set value (K1), and the difference between the primary side and the secondary side of the corresponding phase. It is determined whether the second condition (condition B) that the content rate of the second harmonic included in the difference current is greater than the second set value (K2) is satisfied. The second set value (K2) is smaller than the first set value (K1). Each of the first determining section, the second determining section, and the third determining section (75) determines whether the first condition (condition A) and the second condition (condition B) are both satisfied. Based on this, the output of the relay calculation unit (64) of the corresponding phase is locked.

According to the above configuration, when an inrush current occurs, the second harmonic content rate of one phase among the three phases is always larger than the first set value (K1), and the second harmonic content rate of the other phases is always higher than the first set value (K1). Since the wave content rate becomes larger than the second set value (K2), the occurrence of inrush current can be detected. Furthermore, when an internal failure occurs in the transformer (1) during the generation of inrush current, the second harmonic content rate decreases in the phase where the fault current is included in the detected current value, so the second set value ( Even if K2) is set to a low value, the generation of inrush current will not be detected.

Therefore, we provide a transformer protection relay that detects the occurrence of inrush current and reliably locks the relay output, and also releases the lock and operates the relay if a transformer failure occurs while inrush current is occurring. can. In the subsequent embodiments 2 to 4, a transformer protection relay that more reliably prevents malfunction by combining determination conditions A and B with other determination conditions will be described.

Embodiment 2.
In the transformer protection relay 4 of the second embodiment, the judgment conditions of the inrush judgment section 75 are the combination of judgment conditions A and judgment conditions B in the case of the first embodiment as the operating condition (set condition), and the judgment conditions B It is changed so that the return condition (reset condition) is when the condition is not satisfied for a certain period of time or more. Furthermore, the case where the above-mentioned determination condition D is no longer satisfied may be combined with the return condition. A detailed description will be given below with reference to the drawings.

[Detailed configuration of in-rush determination unit 75]
FIG. 8 is a block diagram showing a specific configuration example of the inrush determination section 75 included in the A-phase calculation section 54 of FIG. 3 in the transformer protection relay 4 of the second embodiment. The inrush determination unit 75 in FIG. 8 further includes a return timer 91 and a flip-flop 90 in addition to the configuration in FIG. 6 . In FIG. 8, the same or corresponding parts as those in FIG. 6 are given the same reference numerals, and the description will not be repeated. Further, the configuration described with reference to FIGS. 1 to 4 is also common to the second embodiment.

As shown in FIG. 8, when the output of the determination unit 83 changes from the inactive state to the active state, the return timer 91 immediately changes its own output to the active state. On the other hand, the return timer 91 changes its own output to an inactive state when the output of the determination unit 83 changes from an active state to an inactive state and the inactive state continues for a set time T1 or more.

The determination condition B that the second harmonic content rate (2f/1f) A of the A phase determined by the determination unit 83 is larger than the set value K2 may not be satisfied temporarily for approximately one cycle. A recovery timer 91 is provided to cover such a temporary decrease in the second harmonic content rate. The set time T1 of the recovery timer 91 is set to approximately 2 cycles.

The flip-flop 90 receives the output signal SG1 of the AND operator 85 at its set terminal, and receives the inverted signal SG2 of the recovery timer 91 at its reset terminal. The flip-flop 90 activates a lock signal for locking the relay output of the current phase when in a set state, and deactivates the above-mentioned lock signal when in a reset state.

Therefore, the flip-flop 90 locks the relay output of its own phase by entering the set state when both the determination condition A and the determination condition B are satisfied. Further, the flip-flop 90 enters a reset state when the state in which the determination condition B is not satisfied continues for a set time T1, thereby releasing the locked state of the relay output of the own phase. In other words, if there is a phase in which the determination condition A is satisfied and the determination condition B is also satisfied, the relay output of that phase is locked. Further, when a state in which the determination condition B is not satisfied continues for a set time T1 in a phase in which the relay output is locked, the lock of the relay output in that phase is released.

According to the configuration of the inrush determination section 75, as in the case of the first embodiment, when an inrush current occurs, the second harmonic content rate of one of the three phases is always set to the set value K1. Since the second harmonic content of the remaining phases becomes larger than the set value K2, the generation of inrush current can be reliably detected. Further, when an internal failure occurs in the three-phase transformer 1, the second harmonic content rate decreases in the phase where the detected current value includes the fault current, since the fault current is mainly composed of the fundamental wave component. Therefore, even if the set value K2 is set to a value considerably lower than the set value K1, the occurrence of inrush current will not be detected in the phase where the detected current value includes the fault current.

The set value K2 used in judgment condition B is set to a value smaller than the normal content rate of the phase where the second harmonic content rate of the inrush current is the minimum, but transiently the second harmonic content rate of this phase It is possible that the wave content rate becomes less than the set value K2. A recovery timer 91 is provided to cover this period of transient decrease in the second harmonic content.

As explained with reference to FIG. 5, when the three-phase transformer 1 is connected to a transmission line with a large ground capacitance, such as a relatively long power cable, the ground capacitance component of the transmission line and the induced components of the transformer windings may cause a resonance phenomenon with a resonant frequency close to the second harmonic. If a second harmonic is detected in the fault current due to this resonance phenomenon, the relay output will continue to be locked. However, this resonance does not pose a major problem because it attenuates within a few cycles, the harmonics become undetectable, and the relay output is unlocked.

FIG. 9 is a timing diagram illustrating the operation of the in-rush determination unit 75 of FIG. 8. The portion indicated by the thick line in FIG. 9 indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 9, power is applied to three-phase transformer 1 at time t1. Due to the generation of the inrush current, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K2 at time t2, so that the determination condition B is satisfied. As a result, the output signal SG2 of the recovery timer 91 becomes active, and the input of the reset terminal of the flip-flop 90 becomes inactive.

At time t3, the second harmonic content rate (2f/1f)B of the B phase exceeds the set value K1, so the determination condition A is satisfied. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes active, so the flip-flop 90 becomes set and the lock signal for locking the relay output becomes active.

Note that in the example of FIG. 9, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. Further, the second harmonic content rate (2f/1f) C of the C phase does not exceed the set value K1.

During time T2 between time t6 and time t7, the second harmonic content rate (2f/1f) A of the A phase temporarily becomes less than or equal to the set value K2. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes inactive. However, since the time T2 is shorter than the set time T1 of the return timer 91, the output signal SG2 of the return timer 91 is maintained in an active state, and the input to the reset terminal of the flip-flop 90 is maintained in an inactive state.

At time t8, a failure occurs in the A phase inside the transformer. As a result, a fault current flows through the A phase, so that the second harmonic content rate (2f/1f) A of the A phase decreases and becomes equal to or less than the set value K2 at time t9. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes inactive.

At time t10, when the set time T1 of the recovery timer 91 has elapsed from time t9, the output signal SG2 of the recovery timer 91 becomes inactive. As a result, the input of the reset terminal of flip-flop 90 becomes active, so flip-flop 90 becomes reset, and the lock signal output from flip-flop 90 becomes inactive. As a result, the A-phase relay output is unlocked.

[Modification of in-rush determination unit 75 in Embodiment 2]
FIG. 10 is a block diagram showing a modification of the inrush determining section 75 of FIG. 8. In FIG. The in-rush determination unit 75 in FIG. 10 differs from the in-rush determination unit 75 in FIG. 8 in that it further includes AND

calculation units

86, 87, and 88 and OR

calculation units

89 and 92.

As shown in FIG. 10, the AND operation unit 86 performs an AND operation on the determination results of the

determination units

80 and 82. The AND operation unit 87 performs an AND operation on the determination results of the

determination units

81 and 82. The AND operator 88 performs an AND operation on the determination results of the

determination units

80 and 81. The OR operator 89 performs an OR operation on the AND operation results of the AND

operators

86, 87, and 88. Therefore, the output of the OR operator 89 is based on the judgment condition D that the content of the second harmonic included in the difference current between the primary side and the secondary side of any two of the three phases is both greater than the set value K1. It shows whether or not it holds true.

The OR operator 92 performs an OR operation between the output of the OR operator 89 indicating the determination result of condition D and the output of the recovery timer 91. Flip-flop 90 receives a signal obtained by inverting output signal SG2 of OR operator 92 at its reset terminal. Since the other points in FIG. 10 are the same as in FIG. 8, the same or corresponding parts are given the same reference numerals and the description will not be repeated.

According to the above configuration, the flip-flop 90 locks the relay output of its own phase by entering the set state when both the determination condition A and the determination condition B are satisfied, which is similar to the case of FIG. be. That is, if there is a phase in which the determination condition A is satisfied and the determination condition B is also satisfied, the relay output of that phase is locked.

On the other hand, the flip-flop 90 enters a reset state when a state in which the judgment condition D is not satisfied and the judgment condition B is not satisfied continues for a set time T1, so that the relay output of the own phase is locked. Release. In other words, if the condition D is not satisfied and the condition B is not satisfied in the phase where the relay output is locked continues for the set time T1, the relay output of the phase is unlocked. be done.

As described above, in the modification shown in FIG. 10, the determination condition D is combined with the reset condition of the flip-flop 90. Judgment condition D is provided to more reliably lock the relay output when an inrush current occurs. Although it is rare that the second harmonic content of only one of the three phases exceeds the set value K1, in most cases the second harmonic content of two of the three phases exceeds the set value K1. Therefore, by using the judgment condition D, even if the period of transient decrease in the second harmonic content rate under the above-mentioned judgment condition B exceeds the set time T1 of the recovery timer 91, the relay output can be prevented from being unlocked. can be complemented by Further, if an internal failure occurs in the three-phase transformer 1 while an inrush current is being generated, the failure current is detected in two phases of the transformer, so that the determination condition D is definitely not satisfied. As described above, the reliability of the transformer protection relay 4 can be improved.

[Effects of Embodiment 2]
As described above, in the transformer protection relay (4), the first relay calculation section (64 of the A phase calculation section 54), the second relay calculation section (64 of the B phase calculation section 55), and the third relay The calculation units (64 of the C-phase calculation unit 56) are provided corresponding to the first phase (A phase), second phase (B phase), and third phase (C phase) of the transformer (1), respectively. , current differential relay calculation is performed based on the fundamental wave component included in the difference current between the primary side and the secondary side of the transformer (1) of the corresponding phase. The first determination section (75 of the A-phase calculation section 54), the second determination section (75 of the B-phase calculation section 55), and the third determination section (75 of the C-phase calculation section 56) are connected to the transformer ( They are provided corresponding to the first phase (A phase), second phase (B phase), and third phase (C phase) of 1), respectively, and perform determination to detect the occurrence of inrush current.

Here, in the case of Embodiment 2, each of the first determining section, the second determining section, and the third determining section (75) is configured to detect the first phase, the second phase, and the third phase. The first condition (condition A) is that the content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one phase is greater than the first set value (K1), and the corresponding phase It is determined whether a second condition (condition B) that the content rate of the second harmonic included in the difference current between the primary side and the secondary side is greater than the second set value (K2) is satisfied.

Each of the first determining section, the second determining section, and the third determining section (75) is set to a set state when both the first condition (condition A) and the second condition (condition B) are satisfied. , and includes a flip-flop (90) that enters a reset state when a state in which the second condition (condition B) is not satisfied continues for a first set time (T1). The flip-flop (90) locks the output of the relay calculation section of the corresponding phase when in the set state, and unlocks the output of the relay calculation section of the corresponding phase when it is in the reset state.

According to the above configuration, when an inrush current occurs, the second harmonic content of one of the three phases is always greater than the first set value (K1), and the second harmonic content of the remaining phases is always higher than the first set value (K1). Since the wave content rate is larger than the second set value (K2), the occurrence of inrush current can be reliably detected. In addition, when an internal failure occurs in the transformer (1) while an inrush current is generated, the second harmonic content rate will decrease in the phase where the fault current is included, so the second set value (K2) should be set to a lower value. In-rush current will not be detected even if the value is set to this value.

Furthermore, when the state in which the second condition (condition B) is not satisfied continues for the first set time (T1), by setting the flip-flop (90) to the reset state, the second harmonic of the corresponding phase is contained. Even if the rate temporarily falls below the second set value (K2), malfunctions can be prevented. In this way, the transformer protection relay detects the occurrence of inrush current and reliably locks the relay output, and also releases the lock and operates the relay if a transformer failure occurs while inrush current is occurring. can be provided.

As a modification of the above, each of the first determining section, the second determining section, and the third determining section (75), in addition to the first condition (condition A) and the second condition (condition B), The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any two phases among the first phase, second phase, and third phase is less than the first setting value (K1). It may be further determined whether the additional condition (condition D) that the value is large is met.

The additional condition (condition D) is combined with the reset condition of the flip-flop (90). That is, the flip-flop (90) enters the reset state when the additional condition (condition D) is not satisfied. As a result, the relay output can be more reliably locked while an inrush current is occurring, and if an internal failure of the three-phase transformer 1 occurs while an inrush current is occurring, the relay output can be more reliably locked. Can be canceled.

Embodiment 3.
The transformer protection relay 4 of the third embodiment is similar to the second embodiment in that among the determination conditions of the inrush determination section 75, determination conditions A and B are operating conditions (set conditions). be. On the other hand, as the return condition (reset condition), a combination of determination condition B and determination condition C described above is used. Further, as in the case of the second embodiment, the case where the above-mentioned determination condition D is no longer satisfied may be further combined as a return condition. A detailed description will be given below with reference to the drawings.

[Detailed configuration of in-rush determination unit 75]
FIG. 11 is a block diagram showing a specific configuration example of the inrush determination section 75 included in the A-phase calculation section 54 of FIG. 3 in the transformer protection relay 4 of the third embodiment. The in-rush determination unit 75 in FIG. 11 differs from the in-rush determination unit 75 in FIG. 8 in that it further includes a determination unit 93 and an OR calculator 92, and is not provided with a return timer 91. In addition, in FIG. 11, the same reference numerals are attached to the same or corresponding parts as in FIGS. 6 and 8, and the description thereof will not be repeated. Further, the configuration described with reference to FIGS. 1 to 4 is also common to the third embodiment.

Referring to FIG. 11, in the case of the inrush determination section 75 included in the A phase calculation section 54, the determination section 93 determines the second harmonic content rate (2f/1f) A of the A phase, which is the own phase, and the A It is determined whether the sum of the third harmonic content rate (3f/1f) A of the phase and the fourth harmonic content rate (4f/1f) A of the A phase is larger than a set value K3.

Here, in the case of the inrush determination unit 75 included in the B-phase calculation unit 55 in FIG. It is determined whether the sum of the third harmonic content rate (3f/1f) B of the B phase and the fourth harmonic content rate (4f/1f) B of the B phase is larger than a set value K3. In addition, in the case of the inrush determination unit 75 included in the C phase calculation unit 56 in FIG. It is determined whether the sum of the third harmonic content rate (3f/1f) C of the phase and the fourth harmonic content rate (4f/1f) C of the C phase is larger than a set value K3. Therefore, for each phase of the three-phase transformer 1, the sum of the contents of the second harmonic, third harmonic, and fourth harmonic included in the difference current between the primary side and the secondary side is the set value. It is determined whether or not the determination condition C, which is greater than K3, is met.

The OR operator 92 performs an OR operation between the output of the determination section 93 indicating the determination result of condition C and the output of the determination section 83 indicating the determination result of condition B.

Flip-flop 90 receives output signal SG1 from AND operator 85 at its set terminal, and receives an inverted signal of output signal SG3 from OR operator 92 at its reset terminal. When flip-flop 90 is in the set state, it activates a lock signal for locking the relay output of its own phase, and when flip-flop 90 is in the reset state, it activates the lock signal.

Therefore, the flip-flop 90 locks the relay output of its own phase by entering the set state when both the determination condition A and the determination condition B are satisfied. In addition, the flip-flop 90 enters a reset state when neither the determination condition B nor the determination condition C is satisfied, thereby releasing the lock of the relay output of the own phase. In other words, when neither determination condition B nor determination condition C is satisfied in a phase in which the relay output is locked, the relay output of that phase is unlocked.

The determination unit 93 may determine whether the above-mentioned condition E is satisfied instead of the condition C. That is, in the case of the A-phase calculation unit 54, the determination unit 93 determines the second harmonic content rate (2f/1f) A of the A phase, which is the own phase, and the fourth harmonic content rate (4f/1f) A of the A phase, which is the own phase. It is determined whether the sum is greater than a set value K4. The same applies to the B-phase calculation section 55 and the C-phase calculation section 56. When a large fault current flows and the current transformer CT is saturated, the current signal is distorted and a third harmonic is generated. By using condition E, which does not use the third harmonic, in place of condition C, it is possible to avoid the influence of the third harmonic. Therefore, unnecessary locking of the relay output can be prevented from continuing when the current transformer CT is saturated.

According to the configuration of the inrush determination unit 75 described above, even if the second harmonic content rate of the A phase temporarily becomes lower than the set value K2 and the condition B is no longer satisfied, the condition C (or the condition By establishing E), it is possible to prevent the relay output from becoming unlocked. Therefore, the recovery timer 91 that was necessary in the second embodiment is no longer necessary, so faster operation can be expected than in the second embodiment.

Furthermore, if an internal failure occurs in the transformer 1 while an inrush current is being generated, the second harmonic content of the failed phase will decrease, so both conditions B and C (or condition E) are not satisfied. It will not be established. Therefore, the relay output is reliably unlocked.

As explained with reference to FIG. 5, when the three-phase transformer 1 is connected to a power transmission line with a large ground capacitance, such as a relatively long power cable, the ground capacitance of the transmission line increases. The capacitive component and the transformer winding-induced component may cause a resonance phenomenon with a resonant frequency close to the second harmonic. Therefore, if the second harmonic is detected in the fault current due to this resonance phenomenon, the relay output will continue to be locked. However, this resonance does not pose a major problem because it attenuates within a few cycles, the harmonics become undetectable, and the relay output is unlocked.

FIG. 12 is a timing diagram illustrating the operation of the in-rush determining section 75 in FIG. 11. The portion indicated by the thick line in FIG. 12 indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 12, power is applied to three-phase transformer 1 at time t1. Due to the generation of the inrush current, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K2 at time t2, so that the determination condition B is satisfied. As a result, the output signal SG3 of the OR operator 92 becomes active, and the input of the reset terminal of the flip-flop 90 becomes inactive.

At time t3, the second harmonic content rate (2f/1f)B of the B phase exceeds the set value K1, so the determination condition A is satisfied. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes active, so the flip-flop 90 becomes set, and the lock signal for locking the A-phase relay output becomes active.

In addition, in the example of FIG. 12, regarding the content rate of the second harmonic in the difference current of the inrush current, the second harmonic content rate (2f/1f) B of the B phase is the largest, and the second harmonic content rate (2f/1f) B of the A phase is the highest. A case is shown in which the content rate (2f/1f) A and the second harmonic content rate (2f/1f) C of the C phase are close to each other and relatively small. The second harmonic content rate (2f/1f) A of the A phase exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. Further, the second harmonic content rate (2f/1f) C of the C phase also exceeds the set value K1 after that, but does not continuously exceed the set value K1. Furthermore, the second harmonic content rate (2f/1f) A of the A phase may transiently decrease below the set value K2.

Specifically, during time T2 between time t6 and time t7, the second harmonic content rate (2f/1f) A of the A phase temporarily becomes less than or equal to the set value K1. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes inactive. However, during this period, the second harmonic content (2f/1f) A, the third harmonic content (3f/1f) A, and the fourth harmonic content (4f/1f) A of phase A are Since the state in which the sum is greater than the set value K3 (condition C is satisfied) is maintained, the output signal SG3 of the OR operator 92 is maintained in the active state. As a result, the input to the reset terminal of flip-flop 90 is maintained in an inactive state.

At the next time t10, the sum of the second harmonic content rate (2f/1f) A, the third harmonic content rate (3f/1f) A, and the fourth harmonic content rate (4f/1f) A of the A phase. becomes below the set value K3. As a result, the output signal SG3 of the OR operator 92 becomes inactive, so that the input of the reset terminal of the flip-flop 90 becomes active. As a result, the flip-flop 90 enters the reset state, the lock signal output from the flip-flop 90 becomes inactive, and the relay output is unlocked.

[Modification of inrush determination unit 75 in Embodiment 3]
FIG. 13 is a block diagram showing a modification of the inrush determination section 75 of FIG. 11. The in-rush determination unit 75 in FIG. 13 differs from the in-rush determination unit 75 in FIG. 11 in that it further includes AND

calculation units

86, 87, and 88 and an OR calculation unit 89. AND

operators

86, 87, 88 and OR operator 89 are connected in the same manner as in FIG. Therefore, the output of the OR operator 89 is based on the judgment condition D that the content of the second harmonic included in the difference current between the primary side and the secondary side of any two of the three phases is both greater than the set value K1. It shows whether or not it holds true.

The OR operator 92 performs an OR operation on the output of the OR operator 89 indicating the determination result of condition D, the output of the determination unit 93 indicating the determination result of condition C, and the output of the determination unit 83 indicating the determination result of condition B. Perform calculations. Flip-flop 90 receives a signal obtained by inverting output signal SG2 of OR operator 92 at its reset terminal. Other points in FIG. 13 are the same as those in FIG. 11, so the same or corresponding parts are given the same reference numerals and the description will not be repeated.

According to the above configuration, the point that the flip-flop 90 locks the relay output of its own phase by entering the set state when both the determination condition A and the determination condition B are satisfied is the same as in the case of FIG. be. That is, if there is a phase in which the determination condition A is satisfied and the determination condition B is also satisfied, the relay output of that phase is locked.

On the other hand, when none of the determination conditions D, B, and C are satisfied, the flip-flop 90 enters the reset state and releases the locked state of the relay output of its own phase. In other words, if judgment condition D is not satisfied and neither judgment condition B nor judgment condition C is satisfied in the phase in which the relay output is locked, the relay output of that phase is unlocked. Ru. Note that instead of the determination condition C, the determination condition E may be used.

As explained with reference to FIG. 10, determination condition D is provided to more reliably lock the relay output when an inrush current occurs. Although it is rare that the second harmonic content of only one of the three phases exceeds the set value K1, in most cases the second harmonic content of two of the three phases exceeds the set value K1. Therefore, by using judgment condition D, even if both judgment condition B and judgment condition C described above may not be satisfied transiently when an inrush current occurs, it is possible to supplement the relay output so that it does not become unlocked. .

[Effects of Embodiment 3]
As described above, in the transformer protection relay 4, the first relay calculation section (64 of the A phase calculation section 54), the second relay calculation section (64 of the B phase calculation section 55), and the third relay calculation section (64 of the C phase calculation unit 56) is provided corresponding to the first phase (A phase), second phase (B phase), and third phase (C phase) of the transformer (1), and Current differential relay calculation is performed based on the fundamental wave component included in the difference current between the primary and secondary sides of the transformer of the phase. The first determination section (75 of the A-phase calculation section 54), the second determination section (75 of the B-phase calculation section 55), and the third determination section (75 of the C-phase calculation section 56) are connected to the transformer ( They are provided corresponding to the first phase (A phase), second phase (B phase), and third phase (C phase) of 1), respectively, and perform determination to detect the occurrence of inrush current.

Here, in the case of Embodiment 3, each of the first determination section, the second determination section, and the third determination section (75) satisfies the first condition (condition A) in the case of Embodiment 2. ) and the second condition (condition B), the content rate of each of the second harmonic, third harmonic, and fourth harmonic included in the difference current between the primary side and the secondary side of the corresponding phase. It is determined whether the third condition (condition C) that the sum of the values is greater than the third set value (K3) is satisfied.

Each of the first determining section, the second determining section, and the third determining section (75) is set to a set state when both the first condition (condition A) and the second condition (condition B) are satisfied. , and includes a flip-flop (90) that enters a reset state when neither the second condition (condition B) nor the third condition (condition C) is satisfied. The flip-flop (90) locks the output of the relay calculation unit (64) of the corresponding phase when in the set state, and unlocks the output of the relay calculation unit (64) of the corresponding phase when it is in the reset state. .

According to the above configuration, as in the first and second embodiments, when an inrush current occurs, the second harmonic content rate of one of the three phases is always set to the first set value (K1 ), and the second harmonic content of the other phase becomes larger than the second set value (K2), so the occurrence of an inrush current can be detected. Furthermore, when an internal failure occurs in the transformer (1) during the generation of inrush current, the second harmonic content rate decreases in the phase where the fault current is included in the detected current value, so the second set value ( Even if K2) is set to a low value, the generation of inrush current will not be detected.

Furthermore, when neither the second condition (condition B) nor the third condition (condition C) is satisfied, by setting the flip-flop (90) to a reset state, the second harmonic content of the corresponding phase is Even if the value temporarily falls below the second set value (K2), malfunctions can be prevented. In this way, the transformer protection relay detects the occurrence of inrush current and reliably locks the relay output, and also releases the lock and operates the relay if a transformer failure occurs while inrush current is occurring. can be provided.

In addition, as a third condition, instead of the above, the sum of the respective content rates of the second harmonic and the fourth harmonic included in the difference current between the primary side and the secondary side of the corresponding phase is the third setting. A condition (condition E) that the value is larger than the value (K4) may be used. By not using the third harmonic, it is possible to prevent malfunctions caused by the third harmonic that occur when the current transformer CT is saturated.

Furthermore, as a modification of the above, each of the first determining section, the second determining section, and the third determining section (75) satisfies the first condition (condition A), the second condition (condition B), and In addition to the third condition (condition C or condition E), the second harmonic contained in the difference current between the primary side and the secondary side of any two phases among the first phase, second phase, and third phase. It may be further determined whether or not the additional condition (condition D) that the content rates of are both greater than the first set value (K1) is satisfied.

Embodiment 4.
In the transformer protection relay 4 of the fourth embodiment, the condition for setting the flip-flop 90 to the reset state in the case of the third embodiment is changed to that only the determination condition C is not satisfied. A detailed description will be given below with reference to the drawings.

[Detailed configuration of in-rush determination unit 75]
FIG. 14 is a block diagram showing a specific configuration example of the inrush determination section 75 included in the A-phase calculation section 54 of FIG. 3 in the transformer protection relay 4 of the fourth embodiment.

The in-rush determination unit 75 in FIG. 14 is not provided with the OR operator 92, and a signal obtained by inverting the logic of the output signal (SG3) of the determination unit 93 indicating the determination result of condition C is used to reset the flip-flop 90. Although directly input to the terminal, the output of the determining unit 83 indicating the determination result of condition B is different from the in-rush determining unit 75 of FIG. Therefore, the flip-flop 90 enters the reset state when the determination condition C is not satisfied, thereby unlocking the relay output of the own phase. In other words, when the determination condition C is not satisfied in a phase in which the relay output is locked, the relay output in that phase is unlocked.

The other points in FIG. 14 are the same as in FIGS. 6, 8, and 11, so the same or corresponding parts are given the same reference numerals and the description will not be repeated. Further, the configuration described with reference to FIGS. 1 to 4 is also common to the fourth embodiment.

FIG. 15 is a timing diagram illustrating the operation of the in-rush determining section 75 in FIG. 14. The portion indicated by the thick line in FIG. 15 indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 15, power is applied to three-phase transformer 1 at time t1. Due to the generation of the inrush current, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K2 at time t2, so that the determination condition B is satisfied.

At time t3, the sum of the second harmonic content rate (2f/1f) A, the third harmonic content rate (3f/1f) A, and the fourth harmonic content rate (4f/1f) A of the A phase is set. Exceeds the value K3. As a result, the output signal SG4 of the OR operator 92 becomes active, and the input of the reset terminal of the flip-flop 90 becomes inactive.

At time t4, the second harmonic content (2f/1f)B of phase B exceeds the set value K1, so judgment condition A is satisfied. As a result, the signal SG1 input to the set terminal of flip-flop 90 becomes active, so that flip-flop 90 becomes set and the lock signal for locking the relay output of phase A becomes active.

Note that in the example of FIG. 15, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K1 at time t5, but does not continuously exceed the set value K1. Further, the second harmonic content rate (2f/1f) C of the C phase does not exceed the set value K1.

During time T2 between time t6 and time t7, the second harmonic content rate (2f/1f) A of the A phase temporarily becomes less than or equal to the set value K1. As a result, the signal SG1 input to the set terminal of the flip-flop 90 becomes inactive. However, unlike the case of the third embodiment, in the case of the fourth embodiment, the failure of the determination condition B is not related to the reset of the flip-flop 90.

At the next time t10, the sum of the second harmonic content rate (2f/1f) A, the third harmonic content rate (3f/1f) A, and the fourth harmonic content rate (4f/1f) A of the A phase. becomes below the set value K3. As a result, the output signal SG4 of the OR operator 92 becomes inactive, so that the input of the reset terminal of the flip-flop 90 becomes active. As a result, the flip-flop 90 enters the reset state, the lock signal output from the flip-flop 90 becomes inactive, and the relay output is unlocked.

[Modification of inrush determination unit 75 in Embodiment 4]
FIG. 16 is a block diagram showing a modification of the inrush determining section 75 of FIG. 14. In FIG. The in-rush determination section 75 in FIG. 16 can be seen as a modification of the in-rush determination section 75 in FIG. 13. That is, in the inrush determination unit 75 of FIG. 16, the output of the OR operator 89 indicating the determination result of condition D and the output of the determination unit 93 indicating the determination result of condition C are input to the OR operator 92. This differs from the in-rush determination unit 75 of FIG. 13 in that the output of the determination unit 83 indicating the determination result of condition B is not input to the OR operator 92.

Therefore, the flip-flop 90 enters the reset state when neither the determination condition C nor the determination condition D is satisfied, thereby releasing the lock of the relay output of the own phase. In other words, when the determination condition D is not satisfied and the determination condition C is not satisfied in the phase in which the relay output is locked, the relay output of the phase is unlocked.

As described with reference to FIGS. 10 and 13, determination condition D is provided to more reliably lock the relay output when an inrush current occurs. Although it is rare that the second harmonic content of only one of the three phases exceeds the set value K1, in most cases the second harmonic content of two of the three phases exceeds the set value K1. Therefore, by using the determination condition D, even if the above-mentioned determination condition C is not satisfied transiently when an inrush current occurs, it can be complemented so that the relay output is not unlocked.

[Effects of Embodiment 4]
Even if the condition for unlocking the relay output as described above is that the judgment condition C is not satisfied, and the judgment condition B is removed, substantially the same effect as in the third embodiment can be obtained. Further, since the set value K3 is a larger value than the set value K2, it is expected that the timing at which the determination condition C fails is earlier than the timing at which the determination condition B fails. As a result, the relay output can be unlocked at an earlier timing.

Furthermore, the determination condition D may be combined with the reset condition of the flip-flop 90. That is, the flip-flop 90 enters the reset state when the determination condition C and the determination condition D are not satisfied. As a result, the relay output can be more reliably locked while an inrush current is occurring, and if an internal failure of the three-phase transformer 1 occurs while an inrush current is occurring, the relay output can be more reliably locked. Can be canceled.

Note that by inputting the output of the OR operator 84 representing the determination result of condition A and the output of the determining unit 93 representing the determination result of condition C to the AND operator 85, both conditions A and C are satisfied. A modification may be considered in which the flip-flop 90 is placed in the set state when the data is stored. Even if this modification is adopted, no problem will occur in many cases. However, when the fault current is large, saturation of the current transformer CT occurs, so that the third harmonic is superimposed on the input of the transformer protection relay 4. As a result, a problem arises because the relay output remains locked. Therefore, as in the case of the first to third embodiments, it is preferable that the condition for locking the relay output is one in which both condition A and condition B are satisfied.

Embodiment 5.
In the transformer protection relay 4 of Embodiment 5, a case will be described in which the occurrence of an inrush current is detected by a combination of the above-mentioned judgment condition A and judgment condition F. By detecting only the second harmonic of each phase, there is an advantage that locking and releasing of the relay output can be controlled with high reliability.

[Detailed configuration of in-rush determination unit 75]
FIG. 17 is a block diagram showing a specific configuration example of the inrush determination section 75 included in the A-phase calculation section 54 of FIG. 3 in the transformer protection relay 4 of the fifth embodiment. Note that in the case of the B-phase calculation section 55 and the C-phase calculation section 56 in FIG. 3, an inrush determination section 75 having the same configuration as in the case of FIG. 17 is used.

Referring to FIG. 17, in-rush determination section 75 includes

determination sections

80, 81, 82,

determination sections

83, 94, 95, OR

operation units

84, 89, and AND

operation units

85, 86, 87, 88. and a return timer 91.

As in the first to fourth embodiments, the determining unit 80 determines whether the second harmonic content rate (2f/1f) A of the A phase is larger than the set value K1. The determination unit 81 determines whether the second harmonic content rate (2f/1f)B of the B phase is larger than the set value K1. The determination unit 82 determines whether the second harmonic content rate (2f/1f) C of the C phase is larger than the set value K1. As mentioned above, the set value K1 is set to a relatively large value (for example, 15%).

determination units

On the other hand, the determination unit 83 determines whether the second harmonic content rate (2f/1f) A of the A phase is larger than the set value K2. The determination unit 94 determines whether the second harmonic content rate (2f/1f)B of the B phase is larger than the set value K2. The determination unit 95 determines whether the second harmonic content rate (2f/1f) C of the C phase is larger than the set value K2. The set value K2 is set to a smaller value (for example, 5%) than the set value K1.

The AND operation unit 86 performs an AND operation on the determination results of the

determination units

83 and 94. The AND operation unit 87 performs an AND operation on the determination results of the

determination units

94 and 95. The AND operator 88 performs an AND operation on the determination results of the

determination units

83 and 95. The OR operator 89 performs an OR operation on the AND operation results of the AND

operators

86, 87, and 88. Therefore, the output of the OR operator 89 is based on the judgment condition F that the content of the second harmonic included in the difference current between the primary side and the secondary side of any two of the three phases is both greater than the set value K2. It shows whether or not it holds true.

When the output of the OR operator 89 changes from an inactive state to an active state, the return timer 91 immediately sets its own output to an active state. On the other hand, the return timer 91 changes its output to an inactive state when the OR calculator 89 changes from an active state to an inactive state and the inactive state continues for a set time T1 or more.

The AND operator 85 combines the output signal of the OR operator 84 indicating the determination result of condition A and the signal obtained by performing delay processing by the recovery timer 91 on the output of the OR operator 89 indicating the determination result of condition F. Perform an AND operation. When the lock signal output from the AND operator 85 becomes active, the relay output is locked, and when the lock signal output from the AND operator 85 becomes inactive, the relay output is unlocked. Ru.

Therefore, when both condition A and condition F are satisfied, the relay output of each phase is locked. On the other hand, when condition A no longer holds true or when condition F no longer holds true for a set time T1, the relay outputs of each phase are unlocked.

According to the above configuration, when an inrush current occurs, the second harmonic content rate of one of the three phases is always larger than the set value K1, so the determination condition A is satisfied. Furthermore, at least immediately after the inrush current is generated, the second harmonic content of two of the three phases is always greater than the set value K2, so the determination condition F is satisfied. Therefore, according to the above configuration, the occurrence of inrush current can be detected reliably.

In addition, if an internal failure of the transformer occurs while an inrush current is being generated, the fault current is always detected in two phases by applying Y/Δ conversion to the current detected by the current transformer CT. be done. In this case, since the fault current is almost a fundamental wave component, the determination condition F no longer holds, and as a result, the relay output is reliably unlocked.

Further, even if the second harmonic content rate temporarily drops below the set value K2 in any two phases, by providing the recovery timer 91, it is possible to prevent the relay output from becoming unlocked. Thereby, malfunction of the transformer protection relay 4 due to inrush current can be prevented.

FIG. 18 is a timing diagram illustrating the operation of the in-rush determining section 75 of FIG. 17. The portion indicated by the bold line in FIG. 18 indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 18, power is applied to three-phase transformer 1 at time t1. Due to the generation of the inrush current, the second harmonic content rate (2f/1f) B of the B phase exceeds the set value K2 at time t2.

At the next time t3, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K2, so the determination condition F is satisfied. Furthermore, at time t3, the second harmonic content rate (2f/1f)B of the B phase exceeds the set value K1, so the determination condition A is satisfied. As a result, the lock signal output from the AND operator 85 becomes active, and the relay output is locked.

Note that in the example of FIG. 18, the second harmonic content rate (2f/1f) A of the A phase exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. Further, the second harmonic content rate (2f/1f) C of the C phase exceeds the set value K2 at time t4, but does not exceed the set value K1.

During time T2 between time t6 and time t7, the second harmonic content rate (2f/1f) A of the A phase becomes equal to or less than the set value K2, and the second harmonic content rate of the C phase temporarily decreases. (2f/1f)C becomes equal to or less than the set value K2. As a result, condition F no longer holds, but since the time T2 is shorter than the set time T1 of the recovery timer 91, the lock signal output from the AND operator 85 is maintained in the active state.

At time t8, a failure occurs in the A phase inside the transformer. As a result, a fault current flows through the A phase and the C phase, so the second harmonic content rate (2f/1f)A of the A phase and the second harmonic content rate (2f/1f)C of the C phase decrease, After time t9, both become equal to or less than the set value K2. As a result, the determination condition F is not satisfied.

At time t10, when the set time T1 of the recovery timer 91 has elapsed from time t9, the lock signal output from the AND calculator 85 changes to an inactive state. This unlocks the relay output.

[Effects of Embodiment 5]
As described above, the transformer protection relay (4) of Embodiment 5 applies to each of the first phase (A phase), second phase (B phase), and third phase (C phase) of the transformer (1). , a relay calculation unit (64) performs current differential relay calculation based on the fundamental wave component included in the difference current between the primary side and the secondary side of the transformer (1), and an inrush The determination unit 75 includes a determination unit (75) that performs determination for detecting generation of current. The determination unit (75) determines whether the content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the first phase, second phase, and third phase is set to a first setting. The first condition (condition A) is that the value is larger than the value (K1), and the second condition included in the difference current between the primary side and the secondary side of any two phases among the first phase, second phase, and third phase. It is determined whether or not the second condition (condition F) that both harmonic content rates are larger than the second set value (K2) is satisfied. The second set value (K2) is smaller than the first set value (K1). The determination unit (75) locks the output of the relay calculation unit (64) when the first condition (condition A) and the second condition (condition F) are both satisfied, and the first condition (condition A) is satisfied. When the second condition (condition F) is no longer satisfied or when the state in which the second condition (condition F) is no longer satisfied continues for the first set time (T1), the output of the relay calculation section is unlocked.

According to the above configuration, when an inrush current occurs, the second harmonic content rate of one of the three phases is always equal to or higher than the first set value (K1). ) holds true. Furthermore, at least immediately after the inrush current is generated, the second harmonic content of two of the three phases is always equal to or higher than the second set value (K2), so the second condition (condition F) is satisfied. Therefore, according to the above configuration, the occurrence of inrush current can be detected reliably.

In addition, if an internal failure occurs in the transformer (1) while an inrush current is being generated, the fault current will always be reduced due to the Y/Δ conversion applied to the detected current of the current transformer CT. Detected in two phases. In this case, since the fault current is almost a fundamental wave component, the second condition (condition F) no longer holds, and as a result, the relay output is reliably unlocked.

Furthermore, even if the second harmonic content rate temporarily drops below the set value K2 in any two phases, the state in which the second condition (condition F) no longer holds continues for the first set time (T1). Since the relay output is unlocked when this occurs, it is possible to prevent the relay output from being unlocked unnecessarily. Thereby, malfunction of the transformer protection relay (4) due to inrush current can be prevented.

Embodiment 6.
It is known that when the iron core of a transformer deteriorates, the magnitude of the inrush current changes (see, for example, Japanese Patent No. 6840306 (Patent Document 2)). Therefore, it is necessary to appropriately change the set values K1 to K4 described in the first to fifth embodiments depending on the degree of deterioration of the transformer core. However, since the magnitude of the inrush current also changes depending on the voltage application phase and the residual magnetic flux, it is difficult to estimate the degree of deterioration of the transformer based on the magnitude of the inrush current.

As a result of various studies, the inventors of the present application found that the amount of change in the length of the low current flat portion that appears in the inrush current waveform (hereinafter referred to as dwell time) is We found that it is related to the degree of deterioration. Since the amount of change in dwell time does not depend on the voltage application phase and residual magnetic flux, the degree of deterioration of the transformer core can be estimated with good reproducibility. This will be explained below with reference to the drawings.

[Functional configuration of transformer arithmetic processing section]
FIG. 19 is a block diagram showing an example of the functional configuration of the A-phase calculation unit 54 in the calculation processing unit 30 in the transformer protection relay 4 of the sixth embodiment.

The A-phase calculation unit 54 in FIG. 19 differs from the A-phase calculation unit 54 in FIG. 4 in that it further includes a dwell time measurement unit 96. The dwell time measurement unit 96 measures the dwell time based on the current waveforms of the A-phase current I'1A on the primary side and the A-phase current I'2A on the secondary side of the three-phase transformer 1. Alternatively, the dwell time measuring section 96 may measure the dwell time based on the difference current waveform (i.e., vector sum) between the A-phase current I'1A on the primary side and the A-phase current I'2A on the secondary side. . In this case, the dwell time measurement unit 96 measures the dwell time based on the difference current IdA output from the harmonic difference current calculation unit 65. The duel time measuring section 96 changes the aforementioned set values K1 to K4 according to the amount of decrease in the measured duel time.

Here, the dwell time decreases depending on the degree of deterioration of the transformer core. Furthermore, the amount of decrease in dwell time is constant regardless of the phase of voltage application to the transformer. Therefore, by increasing the aforementioned set values K1 to K4 in accordance with the amount of decrease in the dwell time, it is possible to accurately determine the occurrence of inrush current. The amount of change in the actual set values K1 to K4 can be determined in advance by experiment or simulation.

Note that the duel time measurement section 96 may be provided in the B-phase calculation section 55 or the C-phase calculation section 56. Alternatively, the dwell time measuring section 96 may measure the dwell time based on a composite current of the difference current between the primary side and the secondary side of each of the A phase, B phase, and C phase. Alternatively, the dwell time measuring section 96 may determine the final amount of change in the dwell time by averaging the amount of change in the dwell time of each phase.

The configuration of the A-phase calculation unit 54 other than the above, for example, the configuration of the inrush determination unit 75, is the same as in Embodiments 1 to 5, so detailed description will not be repeated. Further, the configurations shown in FIGS. 1 to 3 are also common to the sixth embodiment.

[Calculation results of duel time change]
Hereinafter, calculation results of the A-phase inrush current waveform when the voltage application phases are 0°, 30°, 60°, and 120° will be described. Experimentally obtained values were used for the excitation characteristics of the core before and after deterioration. EMTP (Electro-Magnetic Transient Program) for power system analysis was used to calculate the inrush current waveform.

FIG. 20A is a diagram showing the calculation result of the A-phase inrush current waveform when the voltage application phase is 0°. FIG. 20B is an enlarged view of the portion from 0.089 seconds to 0.091 seconds in FIG. 20A. In FIGS. 20A and 20B, the current waveform before deterioration is shown by a solid line, and the current waveform after deterioration is shown by a broken line.

As shown in FIGS. 20A and 20B, due to the deterioration of the iron core, the dwell time decreased from 11.6 ms (milliseconds) to 11.0 ms. Therefore, the amount of change is approximately 0.6 ms.

FIG. 21A is a diagram showing the calculation result of the A-phase inrush current waveform when the voltage application phase is 30°. FIG. 21B is an enlarged view of a portion from 0.0875 seconds to 0.0895 seconds in FIG. 21A. In FIGS. 21A and 21B, the current waveform before deterioration is shown by a solid line, and the current waveform after deterioration is shown by a broken line.

As shown in FIGS. 21A and 21B, due to the deterioration of the iron core, the dwell time decreased from 12.4 ms to 11.9 ms. Therefore, the amount of change is approximately 0.5 ms.

FIG. 22A is a diagram showing the calculation result of the A-phase inrush current waveform when the voltage application phase is 60°. FIG. 22B is an enlarged view of the portion from 0.082 seconds to 0.084 seconds in FIG. 22A. In FIGS. 22A and 22B, the current waveform before deterioration is shown by a solid line, and the current waveform after deterioration is shown by a broken line.

As shown in FIGS. 22A and 22B, due to the deterioration of the iron core, the dwell time decreased from 15.0 ms to 14.4 ms. Therefore, the amount of change is approximately 0.6 ms.

FIG. 23A is a diagram showing the calculation result of the A-phase inrush current waveform when the voltage application phase is 120°. FIG. 23B is an enlarged view of the portion from 0.084 seconds to 0.086 seconds in FIG. 23A. In FIGS. 23A and 23B, the current waveform before deterioration is shown by a solid line, and the current waveform after deterioration is shown by a broken line.

As shown in FIGS. 23A and 23B, due to the deterioration of the iron core, the dwell time decreased from 15.1 ms to 14.5 ms. Therefore, the amount of change is approximately 0.6 ms.

From the above results, it can be seen that the amount of decrease in dwell time due to deterioration of the transformer core is almost constant (approximately 0.6 ms), regardless of the voltage application phase to the transformer.

[Effects of Embodiment 6]
As described above, according to the transformer protection relay 4 of the sixth embodiment, each set value K1 to K4, which is compared with the harmonic content, is changed based on the amount of change in the dwell time. As a result, the set values K1 to K4 can be appropriately changed in response to changes in the inrush current waveform depending on the degree of deterioration of the transformer core, thereby increasing the accuracy of determining whether an inrush current is generated.

The embodiments disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of this application is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

1 Transformer, 2 Primary winding, 3 Secondary winding, 4 Transformer protection relay, 5A, 5B, 5C, 6A, 6B, 6C three-phase line, 10 Input converter, 11 Auxiliary transformer, 20 A/D Conversion unit, 21 analog filter, 22 sample hold circuit, 23 multiplexer, 24 A/D converter, 30 arithmetic processing unit, 31 CPU, 32 RAM, 33 ROM, 34 bus, 40 I/O unit, 41 digital input circuit, 42 Digital output circuit, 50, 51 Y/Δ conversion unit, 52, 53 Gain adjustment unit, 54 A phase calculation unit, 55 B phase calculation unit, 56 C phase calculation unit, 60, 61, 66, 67, 68 filter, 62 Differential current calculation unit, 63 Suppression current calculation unit, 64 Ratio differential relay calculation unit, 65 Harmonic difference current calculation unit, 69, 70, 71 Effective value calculation unit, 72, 73, 74 Content rate calculation unit, 75 Inrush judgment unit, 76, 85, 86, 87, 88 AND operation unit, 80, 81, 82, 83, 93, 94, 95 judgment unit, 84, 89, 92 OR operation unit, 90 flip-flop, 91 return timer , 96 Duel time measurement section, A, B, C, D, E, F Judgment conditions, CT current transformer, GND grounding electrode, K1, K2, K3, K4 setting value, SG1, SG2, SG3, SG4 output signal, T1 Setting time.

Claims

It is provided corresponding to the first phase, second phase, and third phase of the transformer, and is based on the fundamental wave component included in the difference current between the primary side and the secondary side of the transformer of the corresponding phase. a first relay calculation section, a second relay calculation section, and a third relay calculation section that perform current differential relay calculation;
A first determination unit and a second determination unit are provided corresponding to the first phase, the second phase, and the third phase of the transformer, respectively, and perform determination for detecting generation of inrush current. and a third determination unit,
Each of the first determining section, the second determining section, and the third determining section:
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is lower than the first set value. Whether or not the first condition that it is large and the second condition that the content rate of the second harmonic included in the difference current between the primary side and the secondary side of the corresponding phase is larger than a second set value are met. is determined, the second set value is smaller than the first set value,
Each of the first determining section, the second determining section, and the third determining section determines the corresponding phase based on whether both the first condition and the second condition are satisfied. A transformer protection relay that locks the output of the relay calculation section.
Each of the first determining section, the second determining section, and the third determining section enters a set state when both the first condition and the second condition are satisfied, and the second condition is satisfied. including a flip-flop that enters a reset state when a state in which it is not established continues for a first set time;
2. The flip-flop locks the output of the relay calculation unit of the corresponding phase when in the set state, and unlocks the output of the relay calculation unit of the corresponding phase when in the reset state. Transformer protection relays as described in .
Each of the first determining section, the second determining section, and the third determining section determines, in addition to the first condition and the second condition, the primary side and the secondary side of the corresponding phase. Determining whether or not a third condition is satisfied that the sum of the content rates of each of the second harmonic, the third harmonic, and the fourth harmonic included in the difference current is greater than a third set value,
Each of the first determining section, the second determining section, and the third determining section enters a set state when the first condition and the second condition are both satisfied, and the third condition is satisfied. It includes a flip-flop that goes into a reset state if it is not established,
2. The flip-flop locks the output of the relay calculation unit of the corresponding phase when in the set state, and unlocks the output of the relay calculation unit of the corresponding phase when in the reset state. Transformer protection relays as described in .
The transformer protection relay according to claim 3, wherein the flip-flop enters the reset state when neither the second condition nor the third condition is satisfied.
Each of the first determining section, the second determining section, and the third determining section determines, in addition to the first condition and the second condition, the primary side and the secondary side of the corresponding phase. Determining whether or not a third condition is met that the sum of the respective content rates of the second harmonic and the fourth harmonic included in the difference current between the current and the third harmonic is greater than a third set value,
Each of the first determining section, the second determining section, and the third determining section enters a set state when the first condition and the second condition are both satisfied, and the second condition and the second condition are satisfied. including a flip-flop that enters a reset state when none of the third conditions are satisfied;
2. The flip-flop locks the output of the relay calculation unit of the corresponding phase when in the set state, and unlocks the output of the relay calculation unit of the corresponding phase when in the reset state. Transformer protection relays as described in .
Each of the first determining section, the second determining section, and the third determining section further comprises determining the phase of any two of the first phase, the second phase, and the third phase. Determining whether or not the additional condition that the content rate of the second harmonic included in the difference current between the primary side and the secondary side is both larger than the first set value is satisfied;
The transformer protection relay according to any one of claims 2 to 5, wherein the flip-flop is in a reset state if the additional condition is not satisfied.
A relay that performs current differential relay calculation for each of the first phase, second phase, and third phase of the transformer based on a fundamental wave component included in the difference current between the primary side and the secondary side of the transformer. an arithmetic unit;
a determination unit that performs determination to detect generation of inrush current in the transformer, the determination unit comprising:
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is lower than the first set value. The first condition is that it is large, and the content of a second harmonic included in the difference current between the primary side and the secondary side of any two phases among the first phase, the second phase, and the third phase. It is determined whether or not a second condition that both rates are larger than a second set value is met, and the second set value is smaller than the first set value;
The determination unit includes:
When the first condition and the second condition are both satisfied, the output of the relay calculation section is locked, and when the first condition is no longer satisfied or the second condition is no longer satisfied, the output is locked. 1. A transformer protection relay that unlocks the output of the relay calculation section when the set time continues.
further comprising a dwell time measurement unit that measures a dwell time that is a length of a flat portion in an inrush current waveform of the transformer,
The dwell time decreases depending on the degree of deterioration of the iron core of the transformer,
The transformer protection relay according to any one of claims 1 to 7, wherein the dwell time measurement unit changes each set value to be compared with the harmonic content rate according to the amount of decrease in the dwell time.
The transformer protection relay according to any one of claims 1 to 8, wherein the relay calculation unit determines the presence or absence of an internal failure based on a ratio differential principle.
A method for protecting a transformer using a protective relay, the method comprising:
Performing current differential relay calculations for each of the first, second, and third phases of the transformer based on the fundamental wave component included in the difference current between the primary and secondary sides of the transformer. step and
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is lower than the first set value. a step of determining whether or not the first condition of being large is satisfied;
For each phase of the transformer, it is determined whether a second condition that a content rate of a second harmonic included in the difference current between the primary side and the secondary side is greater than a second set value is satisfied. and the second set value is smaller than the first set value, and further,
A transformer protection method, comprising the step of locking a protective relay output of a phase when the first condition is satisfied and there is a phase for which the second condition is satisfied.
Claim further comprising the step of unlocking the protective relay output of the locked phase if the second condition continues for a first set time in the phase in which the protective relay output is locked. 10. The transformer protection method according to 10.
For each phase of the transformer, the sum of the content rates of the second harmonic, the third harmonic, and the fourth harmonic included in the difference current between the primary side and the secondary side is the third harmonic. a step of determining whether a third condition of being larger than a set value is satisfied;
The transformer protection method according to claim 10, further comprising, if the third condition is not satisfied in a phase in which the protective relay output is locked, unlocking the protective relay output of the phase. .
In the step of unlocking the protective relay output, if neither the second condition nor the third condition is satisfied in the phase in which the protective relay output is locked, the protective relay output of the phase is unlocked. The transformer protection method according to claim 12, wherein the transformer protection method is released.
For each phase of the transformer, the sum of the respective content rates of the second harmonic and the fourth harmonic included in the difference current between the primary side and the secondary side is greater than a third set value. a step of determining whether the three conditions are satisfied;
10. The method further comprises the step of unlocking the protective relay output of the phase when neither the second condition nor the third condition is satisfied in the phase in which the protective relay output is locked. Transformer protection methods described in .
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any two phases among the first phase, the second phase, and the third phase is equal to that of the first phase. further comprising the step of determining whether or not an additional condition of being larger than a set value is satisfied;
15. The transformer protection method according to claim 11, wherein in the step of unlocking the protective relay output, the lock is released when the additional condition is not satisfied.
A method for protecting a transformer using a protective relay, the method comprising:
Performing current differential relay calculations for each of the first, second, and third phases of the transformer based on the fundamental wave component included in the difference current between the primary and secondary sides of the transformer. step and
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is lower than the first set value. a step of determining whether or not the first condition of being large is satisfied;
The content rate of the second harmonic included in the difference current between the primary side and the secondary side of any two of the first phase, the second phase, and the third phase is set to a second setting. the second set value is smaller than the first set value, and the second set value is smaller than the first set value, and
locking the protective relay output of each phase when both the first condition and the second condition are satisfied;
A transformer protection method comprising the step of unlocking the protective relay output when the first condition no longer holds true or when the state where the second condition no longer holds true continues for a first set time.
The method further comprises the step of measuring a dwell time, which is the length of a flat portion in an inrush current waveform of the transformer, and changing each set value to be compared with a harmonic content rate according to the amount of decrease in the dwell time. ,
17. The transformer protection method according to claim 10, wherein the dwell time decreases depending on the degree of deterioration of the iron core of the transformer.
The transformer protection method according to any one of claims 10 to 17, wherein the step of performing the current differential relay calculation includes a step of determining the presence or absence of an internal failure based on a ratio differential principle.