JP7250230B1 - Transformer protection relay and transformer protection method - Google Patents

Abstract

In the transformer protection relay (4), the determination unit (75) for each phase sets the content rate of the second harmonic contained in the differential current between the primary side and the secondary side of any one phase to the first set value. (K1) is greater than the first condition (condition A), and the content of the second harmonic contained in the differential current between the primary side and the secondary side of the corresponding phase is greater than the second set value (K2) The output of the relay operation section (64) of the corresponding phase is locked based on whether or not the second condition (condition B) is satisfied. Here, the second set value (K2) is smaller than the first set value (K1).

Description

The present disclosure relates to transformer protection relays and transformer protection methods.

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 the presence or absence of an internal fault according to the ratio differential principle.

A magnetizing inrush current (also called inrush current) may occur when voltage is applied to the transformer. 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 malfunction, the fact that the magnetizing inrush current contains harmonics, particularly the second harmonic, at a certain rate or more with respect to the fundamental wave (rated frequency) component of the generator is used. Specifically, the ratio of the second harmonic component contained in the difference current between the primary winding current and the secondary winding current to the fundamental wave component is calculated as the second harmonic content rate. Differential relay operation is locked or inhibited when the ratio is above a certain value.

However, the inrush current varies greatly depending on the hysteresis characteristics of the iron core of the transformer, the residual magnetic flux, the voltage input phase, etc. or smaller phases are generated. For this reason, in the method of locking the ratio-differential relay operation of only the phase whose second harmonic content rate is greater than the set value (hereinafter referred to as the second harmonic each phase determination method), the second harmonic content Transformer protection relays may malfunction on phases where the ratio is lower than on other phases.

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

Further, Japanese Patent Application Laid-Open No. 01-259720 (Patent Document 1) discloses that when the second harmonic content in any two phases out of the three phases is greater than a set value, all three phases are in ratio differential relay operation. (hereinafter referred to as second harmonic two-phase AND determination method). In this document, the second harmonic two-phase AND decision method is proposed as a complement to the conventional second harmonic each phase decision method.

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

JP-A-01-259720 Japanese Patent No. 6840306

The transformer protection relay of the above-described second harmonic three-phase OR determination method has a problem that the relay cannot be operated when 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 in the case of Δ-connected. Therefore, in the case of a single-phase failure of the transformer, the fault current is included in the line current for the 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 detected for the one phase where the fault current is not detected. continues. As a result, in the transformer protection relay of the second harmonic three-phase OR determination method, the relay operation continues to be locked even if one phase failure occurs in the transformer during the generation of the magnetizing inrush current.

On the other hand, in the transformer protection relay of the second harmonic two-phase AND determination method, if a transformer failure occurs during the generation of inrush current, the second harmonic content rate of any two phases will decrease. do. Therefore, there is an advantage that the lock can be reliably released and the ratio-differential relay can operate.

However, the second harmonic two-phase AND determination type transformer protection relay may not be able to detect the occurrence of an inrush current. In general, the second harmonic content of the inrush current is relatively high for one phase, but relatively low for the other two phases. In the normal case, the inrush current can be detected because the second harmonic content of any two phases exceeds the general set value of 15%. However, depending on the effect of the saturation voltage and residual magnetic flux of the transformer, the second harmonic content of one of the phases may exceed 15%, but the second harmonic content of the other two phases may exceed 15%. may fall below. In that case, the transformer protection relay of the second harmonic two-phase AND determination method cannot prevent malfunction due to the magnetizing inrush current.

Also, it is difficult to set the above set value to less than 10%. If the power system in which the transformer is installed uses a transmission line with a large capacitance component, such as a power cable, the reactor component of the winding of the transformer and the ground capacitance of the transmission line in the event of a fault Harmonics occur due to the resonance of the components. In this case, if the length of the power cable is relatively long, the resonance frequency approaches the second harmonic, so the second harmonic content increases to nearly 10%. For this reason, it is difficult to set the above set value to less than 10%, and it is generally set within the range of 10% to 15%, with 15% being the most common setting.

The present disclosure has been made in consideration of the above problems, and one of its objectives is to reliably detect the occurrence of an inrush current to lock the relay output, and at the same time, to lock the relay output during the occurrence of the inrush current. To provide a transformer protection relay that unlocks and performs relay operation when a transformer failure occurs. Other objects and features of the present disclosure are described in the following embodiments.

The transformer protection relay of one embodiment includes a first relay computing unit, a second relay computing unit, a third relay computing unit, a first determining unit, a second determining unit, and a third determining unit. and a part. The first relay operation unit, the second relay operation unit, and the third relay operation unit are provided corresponding to the first phase, the second phase, and the third phase of the transformer, respectively. A current differential relay calculation is performed based on the fundamental wave component contained in the differential current between the primary side and the secondary side of the transformer. The first determination unit, the second determination unit, and the third determination unit are provided corresponding to the first phase, the second phase, and the third phase of the transformer, respectively, and detect the occurrence of the inrush current. make a decision to Each of the first judging section, the second judging section, and the third judging section has a differential 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 of the second harmonic contained in is greater than the first set value, and the content of the second harmonic contained in the difference current between the primary side and the secondary side of the corresponding phase is the first It is determined whether or not the second condition of being greater than the set value of 2 is established. The second set value is less than the first set value. Each of the first judging section, the second judging section, and the third judging section outputs the output of the relay computing section for the corresponding phase based on whether the first condition and the second condition are both satisfied. to lock.

According to the above embodiment, the determination unit for each phase of the transformer protection relay sets the content rate of the second harmonic contained in the difference current between the primary side and the secondary side of any one phase to the first setting. and the second condition that the content of the second harmonic contained in the differential current between the primary side and the secondary side of the corresponding phase is greater than the second set value. The output of the corresponding relay calculation unit is locked based on whether or not the As a result, the transformer protection relay that reliably detects the occurrence of inrush current and locks the relay output, and unlocks and operates the relay if a transformer failure occurs during the occurrence of inrush current. can provide.

FIG. 4 is a diagram for explaining the connection between a transformer and its protection relay; 2 is a block diagram showing a hardware configuration example of a transformer protection relay in FIG. 1; FIG. 4 is a block diagram for explaining signal processing in an arithmetic processing unit; FIG. FIG. 4 is a block diagram showing a functional configuration example of an A-phase calculation unit in FIG. 3; FIG. 4 is a table summarizing characteristics of individual determination conditions for occurrence of inrush current. FIG. 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; FIG. 7 is a timing chart for explaining the operation of the inrush determination unit in FIG. 6; 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 2; FIG. FIG. 9 is a timing chart for explaining the operation of the inrush determination unit in FIG. 8; FIG. 9 is a block diagram showing a modification of the inrush determination unit in FIG. 8; 4 is a block diagram showing a specific configuration example of an inrush determination unit included in the A-phase calculation unit of FIG. 3 in the transformer protection relay of Embodiment 3; FIG. FIG. 12 is a timing chart for explaining the operation of the inrush determination unit in FIG. 11; FIG. 12 is a block diagram showing a modification of the inrush determination unit in FIG. 11; FIG. 10 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 4; FIG. 15 is a timing chart for explaining the operation of the inrush determination unit in FIG. 14; FIG. 15 is a block diagram showing a modification of the inrush determination unit of FIG. 14; FIG. 10 is a block diagram showing a specific configuration example of an inrush determining section included in the A-phase computing section of FIG. 3 in the transformer protection relay of Embodiment 5; FIG. 18 is a timing chart for explaining the operation of the inrush determination unit in FIG. 17; FIG. 20 is a block diagram showing a functional configuration example of an A-phase calculation unit in a calculation processing unit in the transformer protection relay of Embodiment 6; FIG. 5 is a diagram showing calculation results of an 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 of FIG. 20A; FIG. 5 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 30°; 21B is an enlarged view of the portion from 0.0875 seconds to 0.0895 seconds of FIG. 21A; FIG. FIG. 5 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 60°; 22B is an enlarged view of the portion from 0.082 seconds to 0.084 seconds of FIG. 22A; FIG. FIG. 5 is a diagram showing calculation results of an A-phase inrush current waveform when the voltage application phase is 120°; 23B is an enlarged view of the portion from 0.084 seconds to 0.086 seconds of FIG. 23A; FIG.

Hereinafter, each embodiment will be described in detail with reference to the drawings. 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 protection relay]
FIG. 1 is a diagram for explaining the connection between a transformer and its protective relay. The 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 . The three-phase transformer 1 is not limited to the YΔ transformer, and may be other types of transformers such as a YY transformer and a ΔΔ transformer.

Current transformers CT1A, CT1B, and CT1C (collectively referred to as current transformer CT1) are connected to the three-phase lines 5A, 5B, and 5C on the primary side connected to the primary winding 2 of the three-phase transformer 1, respectively. is provided. The current transformer CT1A detects the current I1A flowing through the A-phase line 5A, the current transformer CT1B detects the current I1B flowing through the B-phase line 5B, and the current transformer CT1C detects the current I1C flowing through the C-phase line 5C. to detect A first end of each current transformer CT1 is connected to a common ground GND, and a 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 That is, the current transformers CT1A, CT1B, and CT1C are Y-connected.

Similarly, the 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 (collectively, current transformers CT2) is provided. The current transformer CT2A detects the current I2A flowing through the A-phase line 6A, the current transformer CT2B detects the current I2B flowing through the B-phase line 6B, and the current transformer CT2C detects the current I2C flowing through the C-phase line 6C. to detect A first end of each current transformer CT2 is connected to a common ground GND, and a 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 That is, the current transformers CT2A, CT2B, CT2C are Y-connected.

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

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

The A/D converter 20 includes analog filters (AF: Analog Filter) 21_1, 21_2, . . . , sample hold circuits (S/H: Sample Hold Circuit) 22_1, 22_2, . , 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 band-pass filter provided to remove aliasing errors during A/D conversion. Each sample hold circuit 22 samples and holds the signal that has passed through the corresponding analog filter 21 at a prescribed sampling frequency. The multiplexer 23 sequentially selects the voltage signals held in the sample 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 them. CPU 31 controls the overall operation of transformer protection relay 4 by operating according to a program. The RAM 32 and ROM 33 are used as main memory for the CPU 31 . By using an electrically rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable ROM) and a flash memory as a storage medium for the ROM 33, programs and set values for signal processing can be stored.

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

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

[Signal processing in arithmetic processing unit]
FIG. 3 is a block diagram for explaining signal processing in the arithmetic processing unit. 3, operation processing unit 30 functionally includes Y/Δ conversion units 50 and 51, gain adjustment units 52 and 53, A phase operation unit 54, B phase operation unit 55, C and a phase calculator 56 .

The Y/Δ converters 50 and 51 convert a Y-connected line current into a Δ-connected line current. A case where the connection method of the YΔ transformer shown in FIG. 1 is Yd1 will be described below. In this case, the primary winding 2 is the Y winding and the secondary winding 3 is the Δ winding, and for the phases of the line currents I1A, I1B, I1C detected by the primary current transformer CT1, The phases of the line currents I2A, I2B, 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 both are matched. Specifically, the line currents I′1A, I′1B, and I′1C on the primary side after conversion are:
I'1A=1IA-I1C (1A)
I'1B=I1B-I1A (1B)
I'1C=I1C-I1B …(1C)
is represented by

Since the secondary winding 3 of the transformer 1 in the case of FIG. 1 is a Δ winding, the Y/Δ conversion section 51 is mounted, but the Y/Δ conversion processing is not performed. Therefore, I'2A=I2A, I'2B=I2B, and I'2C=I2C. In FIG. 3, the Y/Δ conversion section 51 is indicated by a dashed line to indicate that the Y/Δ conversion processing is not performed.

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

Further, instead of the Y/Δ conversion based on the above calculation, the current transformers CT1A, CT1B, and CT1C on the primary side may be Δ-connected so that the phases of the primary and secondary sides of the transformer 1 match. . As a result, the phase of the current detected by the current transformer CT1 on the primary side and the phase of the current detected by the current transformer CT2 on the secondary side can be aligned.

The gain adjustment unit 52 multiplies the Y/Δ-converted primary current by a constant M1 to calculate final primary currents I′1A, I′1B, and I′1C. Similarly, the gain adjustment unit 53 multiplies the secondary current by a constant M2 to calculate final secondary currents I'2A, I'2B, and I'2C. The constants M1 and M2 are the transformation ratio of the three-phase transformer 1 and It is predetermined according to the CT ratios of the 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 a current differential relay calculation and an inrush current calculation for the A phase by a ratio differential method. Presence/absence is determined. Similarly, the B-phase calculation unit 55 uses the B-phase primary current I′1B and the B-phase secondary current I′2B to perform current differential relay calculation and integration for the B phase by the ratio differential method. and determination of the presence or absence of rush current. The C-phase calculation unit 56 uses the C-phase primary side current I′1C and the C-phase secondary side current I′2C to perform a current differential relay calculation and an inrush current calculation for the C-phase by a ratio differential method. 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 the same configuration, the configuration of the A-phase calculation unit 54 will be described below as a representative.

FIG. 4 is a block diagram showing a functional configuration example of the A-phase calculator 54 of FIG. Referring to FIG. 4, A-phase calculation unit 54 includes filters 60, 61, 66, 67 and 68, a difference current calculation unit 62, a suppression current calculation unit 63, a ratio differential relay calculation unit 64, a harmonic It includes a wave difference current calculator 65 , effective value calculators 69 , 70 , 71 , content rate calculators 72 , 73 , 74 , an inrush determiner 75 , and an AND operator 76 .

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

A difference current calculator 62 obtains time-series data of the fundamental wave component I'1A _1f of the A-phase primary side current that has passed through the filter 60 and the fundamental wave component I'2A 1f of the A-phase secondary side current that has passed through the filter ₆₁ . Calculate the effective value of the sum (that is, vector sum) with the time-series data of . Here, by reversing the polarities of the primary-side current transformer CT1 and the secondary-side current transformer CT2, the difference current calculator 62 calculates the difference between the fundamental wave component of the primary-side current and the secondary-side 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)
is represented by 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 electric quantity E.

The suppression current calculator 63 calculates the effective value of the fundamental wave component I'1A _1f of the A-phase primary side current that has passed through the filter 60 and the fundamental wave component I'2A _1f of the A-phase secondary side current that has passed through the filter 61. The scalar sum with the rms 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)
is represented by

The ratio differential relay calculation unit 64 determines whether an internal failure has occurred in the A-phase winding of the three-phase transformer 1 using the difference current IdA _1f and the suppression current IrA _1f . Specifically, the ratio differential relay calculation unit 64 sets the ratio setting values to C1 and C1′ and the minimum setting values to C2 and C2′,
IdA _1f ≧C1×Ird _1f +C2 (4A)
IdA _1f ≧C1′×Ird _1f +C2′ (4B)
is determined to be an internal failure when both are satisfied. 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 calculator 65 calculates the sum (that is, the vector sum) of the time-series data of the A-phase primary side current I′1A and the time-series data of the A-phase secondary side current for extracting the harmonic component. is calculated as the difference current IdA. That is, the difference current IdA is
IdA=I'1A+I'2A (5)
is represented.

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

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

The effective value calculator 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 calculator 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 calculator 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 rate 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. Receive input with value IdA _2f . Then, the content rate 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 rate 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. It receives an input of the effective value of the component IdA _3f . Then, the content rate 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 rate calculator 74 calculates the effective value IdA _1f of the fundamental wave component of the A phase difference current calculated by the differential current calculator 62 and the effective value IdA 1f of the fourth harmonic component of the A phase difference current calculated by the effective value calculator 71 . Receive input with value IdA _4f . Then, the content rate 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 among the harmonic content rates of the phase A, which is the self-phase, calculated by the content rate calculators 72 to 74, and the second harmonic content rate of the other two phases. rate is used to determine whether or not an inrush current is occurring in the self-phase A 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 the presence or absence of the inrush current will be described later with reference to FIGS. 5 to 18. FIG.

The AND calculator 76 calculates a logical product of the relay operation signal output from the ratio-differential relay calculator 64 and a signal obtained by inverting the lock signal output from the inrush determination unit 75 . Therefore, when the lock signal is active, the output of the AND calculator 76 is inactive and the relay output is locked.

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

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

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

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

When the inrush current occurs, the second harmonic content of any one of the three phases becomes considerably large, so according to the determination condition A, the occurrence of the inrush current can be reliably detected. Also, if a single-phase fault occurs inside the transformer while an inrush current is occurring, the fault current will not be detected because the second harmonic is small. However, since the phases that are not the faulty phase contain the inrush current, there is a possibility that the detection of the 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 rate contained in the difference current between the primary side and the secondary side of the own phase is larger than the set value K2 (that is, , second harmonic each phase determination method). The set value K2 is set to a value that allows detection even when the content of the second harmonic contained in the inrush current is minimal. For example, K2=5%.

According to the determination condition B, the set value K2 is set to a value smaller than when the content of the second harmonic contained 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, there is a possibility that the second harmonic content will temporarily fall below the set value K2. In this case, the inrush current is temporarily undetected for the phase in which the second harmonic content rate is temporarily lowered. In addition, when a single-phase failure occurs inside a transformer while an inrush current is occurring, if the transformer is connected to a transmission line with a large capacitance to ground, such as a relatively long power cable, A resonance phenomenon having a resonance frequency close to the second harmonic can occur due to the capacitance component to ground of the transmission line and the inductive component of the windings of the transformer. 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 transmission line with a small capacitance to ground, the fault current contains almost no harmonics, so the second harmonic is not detected immediately after the fault occurs.

Judgment condition C is an individual judgment condition for each phase of the transformer, and it is The condition is that the sum of the respective content rates is greater than the set value K3. The set value K3 is set to a value smaller than the sum of the contents of the second, third and fourth harmonics contained in the inrush current. For example, K3=15%.

According to the determination condition C, the set value K3 is set to a value smaller than the sum of the contents of the second, third, and fourth harmonics contained in the inrush current. The occurrence of inrush current can be reliably detected. There is an advantage that a temporary drop in the second harmonic can be compensated for by the third and fourth harmonics. In addition, when a single-phase failure occurs inside a transformer while an inrush current is occurring, if the transformer is connected to a power cable, resonance will occur due to the capacitive component of the power cable and the inductive component of the transformer. Since the fault current contains harmonics, it is possible to detect these harmonics. However, this resonance decays within a few cycles and the harmonics go undetected. If the fault current contains almost no harmonics because the transformer is connected to the overhead line, the harmonics will not be detected immediately after the fault occurs.

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

In the case of the determination condition D, there may be a case where only one of the three phases has a second harmonic content higher than the set value K1. Therefore, in most cases, the occurrence of inrush current can be detected, but it cannot be said that it can be detected with certainty. In addition, normally, when the transformer is Y-connected, the detected value of the three-phase CT is converted to the line current in the case of Δ-connected. Detected in two phases of the device. Therefore, if a single-phase fault occurs inside the transformer while an inrush current is occurring, the inrush current is reliably undetected.

Judgment condition E is an individual judgment condition for each phase of the transformer, and is the sum of the content rates of the second and fourth harmonics contained in the difference current between the primary side and the secondary side of the own phase. is greater than the set value K4. The set value K4 is set to a value that can be detected even when the content ratio of each of the second and fourth harmonics contained in the inrush current is minimal. 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 contents of the second and fourth harmonics contained in the inrush current, so that the generation of the inrush current is suppressed. can be reliably detected. There is an advantage that a temporary decrease in the second harmonic can be compensated for by the fourth harmonic. In addition, when a single-phase failure occurs inside a transformer while an inrush current is occurring, if the transformer is connected to a transmission line with a large capacitance to ground, such as a relatively long power cable, A resonance phenomenon having a resonance frequency close to the second harmonic can occur due to the capacitance component to ground of the transmission line and the inductive component of the windings of the transformer. 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 go undetected. When the transformer is connected to a transmission line with a small ground capacitance, the fault current contains almost no harmonics, so harmonics are not detected immediately after a fault occurs.

The determination condition F is obtained by changing the set value K1 of the determination condition D to K2. That is, the determination condition F is a condition that the second harmonic content contained in the differential current between the primary side and the secondary side in any two phases out of the three phases is greater than the set value K2. The set value K2 is set to a value that allows detection even when the content of the second harmonic contained in the inrush current is minimal. For example, K2=5%.

According to the determination condition F, the set value K2 is set to a value smaller than when the content of the second harmonic contained 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, there is a possibility that the second harmonic content will temporarily fall below 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 in the case of Δ-connected. Detected in two phases of the device. Therefore, when a single-phase failure occurs inside the transformer while an inrush current is occurring, the inrush current is surely not detected under the judgment condition F.

[Specific Configuration of Inrush Determination Unit]
FIG. 6 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. The determination condition of the inrush determination unit 75 in FIG. 6 is a combination of the determination condition A and the determination condition B described above.

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

As shown in FIG. 6 , the inrush determination section 75 includes determination sections 80 , 81 , 82 and 83 , an OR operator 84 and an AND operator 85 .

The determination unit 80 determines whether or not the A-phase second harmonic content (2f/1f)A is greater than the set value K1. The determination unit 81 determines whether or not the B-phase second harmonic content (2f/1f)B is greater than the set value K1. The determination unit 82 determines whether or not the C-phase second harmonic content (2f/1f)C is greater than the set value K1. As described above, the set value K1 is, for example, 15%, which is a relatively large value.

An 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 of the second harmonic contained in the differential current between the primary side and the secondary side of any one of the A-phase, B-phase, and C-phase is greater than the set value K1. It shows whether or not the judgment condition A of being large is satisfied.

In the case of the A-phase calculator 54, the determination unit 83 determines whether or not 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 considerably smaller than the set value K1.

In the case of the inrush determination unit 75 included in the B-phase calculation unit 55 of FIG. Determine whether it is greater than K2. Further, in the case of the inrush determination unit 75 included in the C-phase calculation unit 56 of 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 contained in the differential current between the primary side and the secondary side is greater than the set value K2 is established. will be

The AND operator 85 performs an AND operation on the output of the OR operator 84 and the output of the determination section 83 . When the lock signal output from the AND operator 85 is active, the relay output of the corresponding phase (phase A in FIG. 6) is locked, and when the lock signal is inactive, the corresponding phase ( A phase) relay output is not locked. The same applies to the B-phase and C-phase. Therefore, when there is a phase in which the determination condition A is satisfied and the determination condition B is satisfied, the protection relay output of the phase is locked.

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

FIG. 7 is a timing chart for explaining the operation of the inrush determination section 75 of FIG. In the part indicated by the thick line in FIG. 7, it indicates that the determination condition is satisfied and the output signal is in the active state.

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

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

At time t8, a fault occurs in phase A inside the transformer. As a result, since a fault current flows through the A phase, the second harmonic content (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.

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

A first relay operation unit, a second relay operation unit, and a third relay operation unit (64) operate the first phase (A phase), second phase (B phase), and third 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 contained in the differential current between the primary side and the secondary side of the transformer of the corresponding phase. The first determination unit, second determination unit, and third determination unit (75) determine the first phase (A phase), second phase (B phase), and third phase (B phase) of the transformer (1). C phase), and performs determination for detecting the occurrence of an inrush current.

Specifically, each of the first determination unit, the second determination unit, and the third determination unit (75) is connected to the primary side of any one of the first phase, the second phase, and the third phase. A first condition (condition A) that the content rate of the second harmonic contained in the differential current with the secondary side is larger than the first set value (K1), and the relationship between the primary side and the secondary side of the corresponding phase It is determined whether or not the second condition (condition B) that the content of the second harmonic contained 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). Then, each of the first determination unit, the second determination unit, and the third determination unit (75) determines whether the first condition (condition A) and the second condition (condition B) are both satisfied. , the output of the relay operation part (64) of the corresponding phase is locked.

According to the above configuration, when an inrush current occurs, the second harmonic content rate of one of the three phases is always greater than the first set value (K1), and the second harmonic content of the other phases is always greater than the first set value (K1). Since the wave content rate is greater than the second set value (K2), occurrence of inrush current can be detected. Further, when an internal fault occurs in the transformer (1) during the generation of the inrush current, the second set value ( Even if K2) is set to a low value, the occurrence of inrush current is no longer detected.

Therefore, we provide a transformer protection relay that detects the occurrence of an inrush current and reliably locks the relay output, and unlocks and performs relay operation when a transformer failure occurs during the occurrence of an inrush current. can. In the following second to fourth embodiments, 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 determination condition of the inrush determination unit 75 is the combination of the determination condition A and the determination condition B in the case of the first embodiment as the operating condition (set condition), and the determination condition B is not satisfied for a certain period of time or longer as a return condition (reset condition). Furthermore, the return condition may be combined with the case where the aforementioned determination condition D is no longer satisfied. A detailed description will be given below with reference to the drawings.

[Detailed Configuration of Inrush Determination Unit 75]
FIG. 8 is a block diagram showing a specific configuration example of the inrush determining section 75 included in the A-phase computing section 54 of FIG. 3 in the transformer protection relay 4 of the second embodiment. 8 further includes a return timer 91 and a flip-flop 90 in addition to the configuration of FIG. 8 that are the same as or correspond to those in FIG. 6 are denoted by the same reference numerals, and description thereof will not be repeated. Moreover, the configuration described with reference to FIGS. 1 to 4 is also common to the case of the second embodiment.

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

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

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

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

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

The set value K2 used in the determination condition B is set to a value smaller than the normal content of the phase that minimizes the second harmonic content of the inrush current. It is possible that the wave content rate becomes equal to or lower than the set value K2. A recovery timer 91 is provided in order to cover the period during which the second harmonic content decreases transiently.

As described with reference to FIG. 5, when the three-phase transformer 1 is connected to a transmission line having a large capacitance to ground, such as a relatively long power cable, the ground capacitance component of the transmission line and the inductive components of the windings of the transformer can cause resonance phenomena with resonance frequencies close to the second harmonic. If a second harmonic is detected in the fault current due to this resonance phenomenon, the lock of the relay output will continue. However, since this resonance decays within a few cycles, the harmonics go undetected and the relay output is unlocked, so this is not a big problem.

FIG. 9 is a timing chart for explaining the operation of the inrush determining section 75 of FIG. In the portion indicated by the thick line in FIG. 9, it indicates that the determination condition is satisfied and the output signal is in the active state.

Referring to FIG. 9, three-phase transformer 1 is energized at time t1. Due to the generation of the inrush current, the second harmonic content (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 return timer 91 becomes active, and the input to the reset terminal of the flip-flop 90 becomes inactive.

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

In the example of FIG. 9, the A-phase second harmonic content (2f/1f)A exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. Also, the second harmonic content (2f/1f)C of the C phase does not exceed the set value K1.

During T2 time from time t6 to time t7, the second harmonic content (2f/1f) A of phase A temporarily becomes equal to or less than 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 recovery timer 91, the output signal SG2 of the recovery timer 91 is kept active and the input of the reset terminal of the flip-flop 90 is kept inactive.

At time t8, a fault occurs in phase A inside the transformer. As a result, since a fault current flows through the A phase, the second harmonic content (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 the flip-flop 90 becomes active, so that the flip-flop 90 becomes reset and the lock signal output from the flip-flop 90 becomes inactive. As a result, the A-phase relay output is unlocked.

[Modification of inrush determination unit 75 in Embodiment 2]
FIG. 10 is a block diagram showing a modification of the inrush determining section 75 of FIG. 10 is different from the inlash determination unit 75 in FIG. 8 in that it further includes AND operators 86, 87, 88 and OR operators 89, 92. FIG.

As shown in FIG. 10 , the AND operator 86 performs an AND operation on the determination results of the determination units 80 and 82 . The AND calculator 87 performs an AND operation on the determination results of the determination units 81 and 82 . An AND calculator 88 performs an AND operation result on the determination results of the determination units 80 and 81 . OR operator 89 performs an OR operation on the AND operation results of AND operators 86 , 87 and 88 . Therefore, the output of the OR operator 89 is determined by the determination condition D that the second harmonic contained in the differential current between the primary side and the secondary side of any two phases out of the three phases is both larger than the set value K1. is established or not.

The OR operator 92 performs an OR operation of the output of the OR operator 89 indicating the determination result of the 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 a reset terminal. Other points in FIG. 10 are the same as in FIG. 8, so the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

According to the above configuration, the self-phase relay output is locked by setting the flip-flop 90 to the set state when both the determination condition A and the determination condition B are satisfied, as in the case of FIG. be. That is, when there is a phase in which the determination condition A is satisfied and the determination condition B is satisfied, the relay output of the phase is locked.

On the other hand, the flip-flop 90 is reset when the determination condition D is not satisfied and the determination condition B is not satisfied continues for the set time T1, whereby the self-phase relay output is locked. release. In other words, when the determination condition D is not satisfied and the relay output is locked, and the state in which the determination condition B is not satisfied 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 reset condition of the flip-flop 90 is combined with the determination condition D. FIG. Judgment condition D is provided to more reliably lock the relay output when an inrush current occurs. Although it is rare that only one of the three phases has a second harmonic content that exceeds the set value K1, in most cases two of the three phases have a second harmonic content that exceeds the set value K1. Therefore, by using the judgment condition D, even if the transitional decrease period of the second harmonic content under the judgment condition B exceeds the set time T1 of the recovery timer 91, the relay output is not unlocked. can be complemented to Further, if an internal fault occurs in the three-phase transformer 1 while the inrush current is occurring, the fault current is detected in two phases of the transformer, so the determination condition D is certainly not satisfied. As described above, the reliability of the transformer protection relay 4 can be improved.

[Effect of Embodiment 2]
As described above, in the transformer protection relay (4), the first relay operation unit (64 of the A-phase operation unit 54), the second relay operation unit (64 of the B-phase operation unit 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), the second phase (B phase), and the third phase (C phase) of the transformer (1). , current differential relay operation is performed based on the fundamental wave component contained in the differential current between the primary side and the secondary side of the transformer (1) of the corresponding phase. The first determination unit (75 of the A phase calculation unit 54), the second determination unit (75 of the B phase calculation unit 55), and the third determination unit (75 of the C phase calculation unit 56) are 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 for detecting the occurrence of inrush current.

Here, in the case of the second embodiment, each of the first determination unit, the second determination unit, and the third determination unit (75) performs the first phase, the second phase, and the third phase. A first condition (condition A) that the content rate of the second harmonic contained in the differential current between the primary side and the secondary side of any one phase is larger than the first set value (K1), and the corresponding phase It is determined whether or not the second condition (condition B) that the content of the second harmonic contained in the differential current between the primary side and the secondary side is greater than the second set value (K2) is met.

Each of the first determination section, the second determination section, and the third determination section (75) is in 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 is reset when the second condition (condition B) is not met for a first set time (T1). The flip-flop (90) locks the output of the corresponding phase relay calculation unit in the set state, and unlocks the output of the corresponding phase relay calculation unit in the reset state.

According to the above configuration, when an inrush current is generated, the second harmonic content rate 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 greater than the first set value (K1). Since the wave content rate is greater than the second set value (K2), the generation of inrush current can be reliably detected. Further, when an internal fault occurs in the transformer (1) during the generation of the inrush current, the second set value (K2) is set low because the second harmonic content decreases in the phase containing the fault current. Inrush current will not be detected even if it is set to a value.

Furthermore, when the state in which the second condition (condition B) is not satisfied continues for the first set time (T1), by resetting the flip-flop (90), the second harmonic content of the corresponding phase is suppressed. Even if the rate temporarily falls below the second set value (K2), malfunction can be prevented. In this way, the transformer protection relay detects the occurrence of inrush current and reliably locks the relay output, and releases the lock and performs relay operation when a transformer failure occurs during the occurrence of inrush current. can provide

As a modification of the above, each of the first determination unit, the second determination unit, and the third determination unit (75), in addition to the first condition (condition A) and the second condition (condition B), The second harmonic contained in the difference current between the primary side and the secondary side of any two phases of the first phase, the second phase, and the third phase is both higher than the first set value (K1) It may be further determined whether or not an additional condition (condition D) of being large is satisfied.

An additional condition (condition D) is combined with the reset condition of flip-flop (90). That is, the flip-flop (90) is reset when the additional condition (condition D) is not met. As a result, the relay output can be locked more reliably during the generation of the inrush current, and the relay output can be reliably locked when an internal failure of the three-phase transformer 1 occurs during the generation of the inrush current. can be released.

Embodiment 3.
In the transformer protection relay 4 of the third embodiment, among the judgment conditions of the inrush judgment section 75, the judgment condition A and the judgment condition B are set as operating conditions (set conditions), as in the case of the second embodiment. be. On the other hand, as the return condition (reset condition), a combination of the determination condition B and the determination condition C described above is used. Further, as in the case of the second embodiment, the case where the aforementioned 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 Inrush Determination Unit 75]
FIG. 11 is a block diagram showing a specific configuration example of the inrush determining section 75 included in the A-phase computing section 54 of FIG. 3 in the transformer protection relay 4 of the third embodiment. 11 is different from the inrush determination unit 75 in FIG. 8 in that it further includes a determination unit 93 and an OR calculator 92 and does not include a recovery timer 91 . In FIG. 11, portions that are the same as or correspond to those in FIGS. 6 and 8 are denoted by the same reference numerals, and description thereof will not be repeated. Moreover, the configuration described with reference to FIGS. 1 to 4 is also common to the case of the third embodiment.

Referring to FIG. 11, in the case of inrush determination unit 75 included in A-phase calculation unit 54, determination unit 93 determines the second harmonic content (2f/1f)A of phase A, which is the self-phase, and A It is determined whether or not 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 greater than the set value K3.

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

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

Flip-flop 90 receives output signal SG1 of AND operator 85 at its set terminal, and receives a signal obtained by inverting output signal SG3 of OR operator 92 at its reset terminal. The flip-flop 90 activates a lock signal for locking the self-phase relay output when in the set state, and deactivates the lock signal when in the reset state.

Therefore, the flip-flop 90 locks the self-phase relay output by being set when both the determination condition A and the determination condition B are satisfied. Further, the flip-flop 90 is reset when neither the determination condition B nor the determination condition C is satisfied, thereby unlocking the self-phase relay output. In other words, when neither the determination condition B nor the determination condition C is satisfied in the phase in which the relay output is locked, the lock of the relay output of the phase is released.

The determination unit 93 may determine whether or not the above-described condition E is satisfied instead of the condition C. That is, the determination unit 93 in the case of the A-phase calculation unit 54 determines the second harmonic content rate (2f/1f) A of the self-phase A and the fourth harmonic content rate (4f/1f) A of the A-phase. is greater than the set value K4. The same applies to the B-phase calculator 55 and the C-phase calculator 56 . If a large fault current saturates the current transformer CT, the current signal will be distorted to produce the third harmonic. By using the condition E that does not use the third harmonic in place of the condition C, it is possible to avoid the influence of the third harmonic. Therefore, it is possible to prevent unnecessary continuation of locking of the relay output 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 transiently becomes equal to or less 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 being unlocked. Therefore, since the recovery timer 91 that is required in the second embodiment is no longer necessary, a faster operation than in the second embodiment can be expected.

Moreover, if an internal fault occurs in the transformer 1 during the generation of the inrush current, the second harmonic content rate of the faulty phase decreases. cease to exist. Therefore, the lock of the relay output is reliably released.

As described with reference to FIG. 5, when the three-phase transformer 1 is connected to a transmission line having a large ground capacitance, such as a relatively long power cable, the ground static electricity of the transmission line A resonance phenomenon with a resonance frequency close to the second harmonic may occur due to the capacitive component and the winding inductive component of the transformer. 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, since this resonance decays within a few cycles, the harmonics go undetected and the relay output is unlocked, so this is not a big problem.

FIG. 12 is a timing chart for explaining the operation of the inrush determining section 75 of FIG. 12 indicates that the determination condition is satisfied and the output signal is in the active state in the portion indicated by the thick line.

Referring to FIG. 12, three-phase transformer 1 is energized at time t1. Due to the generation of the inrush current, the second harmonic content (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 calculator 92 becomes active, and the input to the reset terminal of the flip-flop 90 becomes inactive.

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

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 of the A phase is the highest. A case is shown in which the content (2f/1f)A and the second harmonic content (2f/1f)C of the C phase are close to each other and relatively small. The A-phase second harmonic content (2f/1f)A exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. In addition, the second harmonic content (2f/1f)C of the C phase also exceeds the set value K1 thereafter, but does not exceed the set value K1 continuously. Furthermore, the A-phase second harmonic content (2f/1f)A may transiently drop below the set value K2.

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

At time t8, a fault occurs in phase A inside the transformer. As a result, since a fault current flows through the A phase, the second harmonic content (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 the next time t10, the sum of the phase A second harmonic content (2f/1f)A, third harmonic content (3f/1f)A, and fourth harmonic content (4f/1f)A becomes equal to or less than the set value K3. As a result, the output signal SG3 of the OR calculator 92 becomes inactive, and the input to the reset terminal of the flip-flop 90 becomes active. As a result, the flip-flop 90 is reset, the lock signal output from the flip-flop 90 is inactive, and the relay output is unlocked.

[Modified Example of Inrush Determination Unit 75 in Embodiment 3]
FIG. 13 is a block diagram showing a modification of the inrush determining section 75 of FIG. 11. As shown in FIG. 13 differs from the inlash determination unit 75 in FIG. 11 in that it further includes AND operators 86, 87, 88 and an OR operator 89. Inrush determination unit 75 in FIG. 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 determined by the determination condition D that the second harmonic contained in the differential current between the primary side and the secondary side of any two phases out of the three phases is both larger than the set value K1. is established or not.

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

According to the above configuration, the self-phase relay output is locked by setting the flip-flop 90 to the set state when both the determination condition A and the determination condition B are satisfied, as in the case of FIG. be. That is, when there is a phase in which the determination condition A is satisfied and the determination condition B is satisfied, the relay output of the phase is locked.

On the other hand, the flip-flop 90 is reset when none of the determination conditions D, B, and C is satisfied, thereby releasing the locked state of the self-phase relay output. In other words, when the determination condition D is not satisfied and neither the determination condition B nor the determination condition C is satisfied in the phase for which the relay output is locked, the lock of the relay output of the phase is released. be. In addition, instead of the determination condition C, the determination condition E may be used.

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

[Effect of Embodiment 3]
As described above, in the transformer protection relay 4, the first relay operation unit (64 of the A-phase operation unit 54), the second relay operation unit (64 of the B-phase operation unit 55), and the third relay operation unit (64 of the C-phase calculation unit 56) are provided corresponding to the first phase (A phase), the second phase (B phase), and the third phase (C phase) of the transformer (1). A current differential relay operation is performed based on the fundamental wave component included in the differential current between the primary side and the secondary side of the transformer of the corresponding phase. The first determination unit (75 of the A phase calculation unit 54), the second determination unit (75 of the B phase calculation unit 55), and the third determination unit (75 of the C phase calculation unit 56) are 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 for detecting the occurrence of inrush current.

Here, in the case of the third embodiment, each of the first determination unit, the second determination unit, and the third determination unit (75) is the first condition (condition A ) and in addition to the second condition (condition B), the content ratio of each of the second harmonic, the third harmonic, and the fourth harmonic contained in the differential current between the primary side and the secondary side of the corresponding phase is greater than the third set value (K3).

Each of the first determination section, the second determination section, and the third determination section (75) is in 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 is reset when neither the second condition (condition B) nor the third condition (condition C) is satisfied. The flip-flop (90) locks the output of the corresponding phase relay operation part (64) in the set state, and unlocks the output of the corresponding phase relay operation part (64) in the reset state. .

According to the above configuration, as in the case of the first and second embodiments, when an inrush current is generated, 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 phases is greater than the second set value (K2), so the occurrence of the inrush current can be detected. Further, when an internal fault occurs in the transformer (1) during the generation of the inrush current, the second set value ( Even if K2) is set to a low value, the occurrence of inrush current is no longer detected.

Furthermore, when neither the second condition (condition B) nor the third condition (condition C) is satisfied, by resetting the flip-flop (90), the second harmonic content of the corresponding phase can be prevented from malfunctioning even if temporarily becomes equal to or less than the second set value (K2). In this way, the transformer protection relay detects the occurrence of an inrush current and reliably locks the relay output, and releases the lock and performs relay operation when a transformer failure occurs during the occurrence of an inrush current. can provide

As the third condition, instead of the above, the sum of the contents of the second harmonics and the fourth harmonics contained 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 greater than the value (K4) may be used. By not using the third harmonic, malfunction caused by the third harmonic that occurs when the current transformer CT saturates can be prevented.

Furthermore, as a modification of the above, each of the first determination unit, the second determination unit, and the third determination unit (75) can perform 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 differential current between the primary side and the secondary side of any two phases of the first phase, the second phase, and the third phase It may be further determined whether or not an additional condition (condition D) that the contents of both are greater than the first set value (K1) is satisfied.

An additional condition (condition D) is combined with the reset condition of flip-flop (90). That is, the flip-flop (90) is reset when the additional condition (condition D) is not met. As a result, the relay output can be locked more reliably during the generation of the inrush current, and the relay output can be reliably locked when an internal failure of the three-phase transformer 1 occurs during the generation of the inrush current. can be released.

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

[Detailed Configuration of Inrush Determination Unit 75]
FIG. 14 is a block diagram showing a specific configuration example of the inrush determining section 75 included in the A-phase computing section 54 of FIG. 3 in the transformer protection relay 4 of the fourth embodiment.

The inrush determination unit 75 in FIG. 14 is not provided with the OR operator 92, and the signal obtained by inverting the logic of the output signal (SG3) of the determination unit 93 indicating the determination result of the condition C is the reset of the flip-flop 90. 11 in that the output of the determination section 83 indicating the determination result of the condition B is not used as the reset condition of the flip-flop 90, although it is directly input to the terminal. Therefore, the flip-flop 90 is reset when the determination condition C is not satisfied, thereby unlocking the self-phase relay output. In other words, when the determination condition C is not satisfied in the phase whose relay output is locked, the lock of the relay output of that phase is released.

14 are the same as those of FIGS. 6, 8, and 11, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. Also, the configuration described with reference to FIGS. 1 to 4 is common to the fourth embodiment.

FIG. 15 is a timing chart for explaining the operation of the inrush determining section 75 of FIG. 15 indicates that the determination condition is satisfied and the output signal is in the active state in the portion indicated by the thick line.

Referring to FIG. 15, three-phase transformer 1 is energized at time t1. Due to the generation of the inrush current, the second harmonic content (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 (2f/1f)A, the third harmonic content (3f/1f)A, and the fourth harmonic content (4f/1f)A of phase A is set. exceeds the value K3. As a result, the output signal SG4 of the OR operator 92 becomes active, and the input to the reset terminal of the flip-flop 90 becomes inactive.

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

In the example of FIG. 15, the A-phase second harmonic content (2f/1f)A exceeds the set value K1 at time t5, but does not continuously exceed the set value K1. Also, the second harmonic content (2f/1f)C of the C phase does not exceed the set value K1.

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

At time t8, a fault occurs in phase A inside the transformer. As a result, since a fault current flows through the A phase, the second harmonic content (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 the next time t10, the sum of the phase A second harmonic content (2f/1f)A, third harmonic content (3f/1f)A, and fourth harmonic content (4f/1f)A becomes equal to or less than the set value K3. As a result, the output signal SG4 of the OR calculator 92 becomes inactive, and the input to the reset terminal of the flip-flop 90 becomes active. As a result, the flip-flop 90 is reset, the lock signal output from the flip-flop 90 is inactive, and the relay output is unlocked.

[Modified Example 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. The inlash determination unit 75 of FIG. 16 can be viewed as a modification of the inlash determination unit 75 of FIG. 16, the output of the OR calculator 89 indicating the decision result of the condition D and the output of the decision unit 93 indicating the decision result of the condition C are input to the OR calculator 92. , in that the output of the determination unit 83 indicating the determination result of condition B is not input to the OR operator 92, unlike the inrush determination unit 75 of FIG.

Therefore, the flip-flop 90 is reset when neither the determination condition C nor the determination condition D is satisfied, thereby unlocking the self-phase relay output. 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 lock of the relay output of the phase is released.

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 only one of the three phases has a second harmonic content that exceeds the set value K1, in most cases two of the three phases have a second harmonic content that exceeds the set value K1. Therefore, by using the determination condition D, even if the above-described determination condition C is transiently not satisfied when an inrush current occurs, it is possible to compensate so that the relay output is not unlocked.

[Effect of Embodiment 4]
Assuming that the determination condition C is not established as the condition for unlocking the relay output as described above, almost the same effect as in the case of the third embodiment can be obtained even if the determination condition B is removed. Also, 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 is not satisfied is earlier than the timing at which the determination condition B is not satisfied. 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 is reset when the determination condition C and the determination condition D are not satisfied. As a result, the relay output can be locked more reliably during the generation of the inrush current, and the relay output can be reliably locked when an internal failure of the three-phase transformer 1 occurs during the generation of the inrush current. can be released.

By inputting the output of the OR operator 84 representing the determination result of the condition A and the output of the determination unit 93 representing the determination result of the condition C to the AND operator 85, both the condition A and the condition C are satisfied. A modification is conceivable in which the flip-flop 90 is set in the set state. Even if this modification is adopted, no problem arises in many cases. However, when the fault current is large, the third harmonic is superimposed on the input of the transformer protection relay 4 due to saturation of the current transformer CT. This results in a problem because the relay output remains locked. Therefore, it is preferable that the condition for locking the relay output is that both condition A and condition B are satisfied, as in the first to third embodiments.

Embodiment 5.
In the transformer protection relay 4 of Embodiment 5, the case where the occurrence of the inrush current is detected by the combination of the determination condition A and the determination condition F described above will be described. Advantageously, only the second harmonic of each phase can be detected to control the locking and unlocking of the relay output with high reliability.

[Detailed Configuration of Inrush Determination Unit 75]
FIG. 17 is a block diagram showing a specific configuration example of the inrush determining section 75 included in the A-phase computing section 54 of FIG. 3 in the transformer protection relay 4 of the fifth embodiment. 3, the inrush determination unit 75 having the same configuration as that of FIG. 17 is used.

17, inrush determination unit 75 includes determination units 80, 81, 82; determination units 83, 94, 95; OR operators 84, 89; AND operators 85, 86, 87, 88; and a return timer 91 .

As in the first to fourth embodiments, determination unit 80 determines whether or not second harmonic content (2f/1f)A of phase A is greater than set value K1. The determination unit 81 determines whether or not the B-phase second harmonic content (2f/1f)B is greater than the set value K1. The determination unit 82 determines whether or not the C-phase second harmonic content (2f/1f)C is greater than the set value K1. As described above, the set value K1 is set to a relatively large value (eg, 15%).

An 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 of the second harmonic contained in the differential current between the primary side and the secondary side of any one of the A-phase, B-phase, and C-phase is greater than the set value K1. It shows whether or not the judgment condition A of being large is satisfied.

On the other hand, the determination unit 83 determines whether or not the A-phase second harmonic content (2f/1f)A is greater than the set value K2. The determination unit 94 determines whether or not the B-phase second harmonic content (2f/1f)B is greater than the set value K2. The determination unit 95 determines whether or not the C-phase second harmonic content (2f/1f)C is greater than the set value K2. The set value K2 is set to a value (for example, 5%) smaller than the set value K1.

The AND calculator 86 performs an AND operation on the determination results of the determination units 83 and 94 . The AND operator 87 performs an AND operation on the determination results of the determination units 94 and 95 . The AND operator 88 performs an AND operation result on the determination results of the determination units 83 and 95 . OR operator 89 performs an OR operation on the AND operation results of AND operators 86 , 87 and 88 . Therefore, the output of the OR operator 89 is determined by the judgment condition F that the second harmonic contained in the differential current between the primary side and the secondary side of any two phases out of the three phases is both larger than the set value K2. is established or not.

The return timer 91 immediately activates its own output when the output of the OR calculator 89 changes from the inactive state to the active state. On the other hand, the return timer 91 makes its own output inactive when the OR operator 89 changes from active to inactive and the inactive state continues for the set time T1 or longer.

The AND operator 85 outputs the output signal of the OR operator 84 indicating the judgment result of the condition A, and the output of the OR operator 89 showing the judgment result of the condition F, which is delayed by the return timer 91. Perform an AND operation. The relay output is locked when the lock signal output from the AND operator 85 becomes active, and the relay output is unlocked when the lock signal output from the AND operator 85 becomes inactive. be.

Therefore, when condition A and condition F are both satisfied, the relay output of each phase is locked. On the other hand, when the condition A is no longer satisfied or when the condition F is not satisfied continues for the set time T1, the lock of the relay output of each phase is released.

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

Also, if an internal fault occurs in the transformer during the generation of the inrush current, the fault current is always detected in two phases by performing Y/Δ conversion on the detected current of the current transformer CT. be done. In this case, since the fault current is mostly the fundamental wave component, the determination condition F is no longer satisfied, and as a result, the lock of the relay output is reliably released.

Further, even if the second harmonic content in any two phases temporarily falls below the set value K2, the provision of the return timer 91 can prevent the relay output from being unlocked. This can prevent the transformer protection relay 4 from malfunctioning due to the inrush current.

FIG. 18 is a timing chart for explaining the operation of the inrush determining section 75 of FIG. 18 indicates that the determination condition is satisfied and the output signal is in the active state in the portion indicated by the thick line.

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

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

In the example of FIG. 18, the A-phase second harmonic content (2f/1f)A exceeds the set value K1 at time t4, but does not continuously exceed the set value K1. Also, 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 the time T2 from time t6 to time t7, the second harmonic content (2f/1f) A of the A phase temporarily becomes equal to or less than the set value K2, and the second harmonic content of the C phase (2f/1f) C becomes equal to or less than the set value K2. As a result, the condition F is no longer satisfied, but since the time T2 is shorter than the set time T1 of the recovery timer 91, the lock signal output from the AND calculator 85 is maintained in an active state.

At time t8, a fault occurs in phase A inside the transformer. As a result, a fault current flows in the A phase and the C phase, so that 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, Both become equal to or less than the set value K2 after time t9. As a result, the determination condition F becomes unsatisfied.

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

[Effect of Embodiment 5]
As described above, the transformer protection relay (4) according to the fifth embodiment is designed for 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) that performs a current differential relay calculation based on the fundamental wave component contained in the difference current between the primary side and the secondary side of the transformer (1), and an inrush in the transformer (1) and a determination unit (75) that performs determination for detecting the generation of the current. The determination unit (75) sets the content rate of the second harmonic contained in the differential current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase to the first setting. A first condition (condition A) that the value (K1) is greater than the value (K1), and a second It is determined whether or not the second condition (condition F) that both of the harmonic content rates are greater than the second set value (K2) is met. The second set value (K2) is less than the first set value (K1). A determination unit (75) locks the output of the relay operation unit (64) when both the first condition (condition A) and the second condition (condition F) are satisfied, and the first condition (condition A) is 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 lock of the relay calculation unit is released.

According to the above configuration, when an inrush current is generated, the second harmonic content of one of the three phases is always equal to or higher than the first set value (K1), so the first condition (condition A ) holds. 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 established. Therefore, according to the above configuration, it is possible to reliably detect the occurrence of the inrush current.

Further, if an internal fault occurs in the transformer (1) during the generation of the inrush current, the fault current will always be Detected in two phases. In this case, since the fault current is mostly the fundamental wave component, the second condition (condition F) is no longer satisfied, and as a result, the lock of the relay output is reliably released.

In addition, even if the second harmonic content in any two phases temporarily falls below the set value K2, the state in which the second condition (condition F) is no longer satisfied continues for the first set time (T1). Since the lock of the relay output is released in this case, it is possible to prevent the relay output from being unnecessarily unlocked. This can prevent the transformer protection relay (4) from malfunctioning due to the inrush current.

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 according to the degree of deterioration of the iron core of the transformer. 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 from the magnitude of the inrush current.

The inventors of the present application conducted various studies and found that the amount of change in the length of the flat portion of the low current appearing in the inrush current waveform (hereinafter referred to as dwell time) is It was found to be 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 iron core of the transformer can be estimated with good reproducibility. Description will be made below with reference to the drawings.

[Functional Configuration of Arithmetic Processing Unit of Transformer]
FIG. 19 is a block diagram showing a functional configuration example of the A-phase calculation section 54 in the calculation processing section 30 in the transformer protection relay 4 of the sixth embodiment.

The A-phase computing section 54 of FIG. 19 is different from the A-phase computing section 54 of FIG. 4 in that it further includes a dwell time measuring section 96 . The dwell time measuring 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 differential current waveform (that is, the vector sum) of 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 section 96 measures the dwell time based on the difference current IdA output from the harmonic difference current calculation section 65 . The duel time measurement unit 96 changes the set values K1 to K4 according to the amount of decrease in the measured duel time.

Here, the dwell time decreases according to the degree of deterioration of the iron core of the transformer. Also, the amount of decrease in dwell time is constant regardless of the voltage input phase to the transformer. Therefore, by increasing the aforementioned set values K1 to K4 in accordance with the amount of decrease in dwell time, occurrence of inrush current can be accurately determined. The amount of change of the actual set values K1 to K4 can be determined in advance by experiments or simulations.

Note that the dwell time measurement unit 96 may be provided in the B-phase calculation unit 55 or may be provided in the C-phase calculation unit 56 . Alternatively, the dwell time measuring section 96 may measure the dwell time based on the combined current of the difference currents between the primary and secondary sides 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 dwell time by averaging the amount of change in dwell time of each phase.

Other than the above, the configuration of A-phase calculation unit 54, for example, the configuration of inrush determination unit 75, is the same as in the first to fifth embodiments, and detailed description thereof will not be repeated. 1 to 3 are also common to the sixth embodiment.

[Calculation result of duel time change]
Calculation results of the A-phase inrush current waveform when the voltage application phases are 0°, 30°, 60°, and 120° will be described below. Experimentally obtained values were used for the excitation characteristics of the iron 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 a calculation result of an 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 of FIG. 20A. In FIGS. 20A and 20B, the solid line indicates the current waveform before deterioration, and the broken line indicates the current waveform after deterioration.

As shown in FIGS. 20A and 20B, the core deterioration reduced the dwell time 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 a calculation result of an A-phase inrush current waveform when the voltage application phase is 30°. FIG. 21B is an enlarged view of the portion from 0.0875 seconds to 0.0895 seconds of FIG. 21A. In FIGS. 21A and 21B, the solid line indicates the current waveform before deterioration, and the broken line indicates the current waveform after deterioration.

As shown in FIGS. 21A and 21B, due to core deterioration, 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 calculation results of an 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 of FIG. 22A. In FIGS. 22A and 22B, the solid line indicates the current waveform before deterioration, and the dashed line indicates the current waveform after deterioration.

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

FIG. 23A is a diagram showing calculation results of an 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 of FIG. 23A. In FIGS. 23A and 23B, the solid line indicates the current waveform before deterioration, and the broken line indicates the current waveform after deterioration.

As shown in FIGS. 23A and 23B, the core deterioration reduced the dwell time 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 decrease in dwell time due to deterioration of the iron core of the transformer is almost constant (approximately 0.6 ms) regardless of the voltage input phase to the transformer.

[Effect of Embodiment 6]
As described above, according to the transformer protection relay 4 of the sixth embodiment, each set value K1 to K4 to be compared with the harmonic content is changed based on the amount of change in dwell time. As a result, the set values K1 to K4 can be appropriately changed in response to changes in the inrush current waveform according to the degree of deterioration of the iron core of the transformer, so the accuracy of determining whether or not the inrush current is generated can be improved.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of this application is indicated by the scope of claims rather than the above description, and is intended to include all changes within the meaning and scope of equivalence to the scope of claims.

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 section, 21 analog filter, 22 sample hold circuit, 23 multiplexer, 24 A/D converter, 30 arithmetic processing section, 31 CPU, 32 RAM, 33 ROM, 34 bus, 40 I/O section, 41 digital input circuit, 42 digital output circuit, 50, 51 Y/Δ conversion section, 52, 53 gain adjustment section, 54 A phase calculation section, 55 B phase calculation section, 56 C phase calculation section, 60, 61, 66, 67, 68 filter, 62 difference current calculator, 63 suppression current calculator, 64 ratio differential relay calculator, 65 difference current calculator for harmonics, 69, 70, 71 effective value calculator, 72, 73, 74 content rate calculator, 75 Inrush determination unit 76, 85, 86, 87, 88 AND operator 80, 81, 82, 83, 93, 94, 95 determination unit 84, 89, 92 OR operator 90 flip-flop 91 return timer , 96 dwell time measurement unit A, B, C, D, E, F judgment condition CT current transformer GND ground electrode K1, K2, K3, K4 set value SG1, SG2, SG3, SG4 output signal, T1 set time.

Claims (18)

provided corresponding to the first phase, the second phase, and the third phase of the transformer, respectively, based on the fundamental wave component contained in the differential current between the primary side and the secondary side of the transformer of the corresponding phase a first relay computation unit, a second relay computation unit, and a third relay computation unit that perform current differential relay computation;
a first determination unit and a second determination provided corresponding to the first phase, the second phase, and the third phase of the transformer, respectively, for performing determination for detecting occurrence of an inrush current; and a third determination unit,
Each of the first determination unit, the second determination unit, and the third determination unit,
The second harmonic contained in the differential current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is higher than a first set value. Presence or absence of satisfaction of the first condition that the current is large and the second condition that the content of the second harmonic contained in the difference current between the primary side and the secondary side of the corresponding phase is greater than the second set value. and the second set value is smaller than the first set value,
Each of the first judging section, the second judging section, and the third judging section determines whether or not the first condition and the second condition are both satisfied. A transformer protection relay that locks the output of the relay calculator. Each of the first judging section, the second judging section, and the third judging section enters a set state when both the first condition and the second condition are satisfied, and the second condition is Including a flip-flop that enters a reset state when the state that is not established continues for a first set time,
2. The flip-flop locks the output of the relay operation unit of the corresponding phase when in the set state, and unlocks the output of the relay operation unit of the corresponding phase when in the reset state. Transformer protection relay as described in . Each of the first determination section, the second determination section, and the third determination section satisfies the first condition and the second condition, as well as the primary side and the secondary side of the corresponding phase. Determining whether the third condition is satisfied that the sum of the contents of the second harmonic, the third harmonic, and the fourth harmonic contained in the difference current is greater than the third set value,
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 third condition is includes a flip-flop that goes into a reset state if not true,
2. The flip-flop locks the output of the relay operation unit of the corresponding phase when in the set state, and unlocks the output of the relay operation unit of the corresponding phase when in the reset state. Transformer protection relay as described in . 4. The transformer protection relay of claim 3, wherein said flip-flop is in said reset state when neither said second condition nor said third condition is met. Each of the first determination section, the second determination section, and the third determination section satisfies the first condition and the second condition, as well as the primary side and the secondary side of the corresponding phase. Determining whether or not the third condition is satisfied that the sum of the contents of the second and fourth harmonics contained in the difference current is greater than the third set value,
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 including a flip-flop that is reset when none of the third conditions are satisfied;
2. The flip-flop locks the output of the relay operation unit of the corresponding phase when in the set state, and unlocks the output of the relay operation unit of the corresponding phase when in the reset state. Transformer protection relay as described in . Each of the first determining section, the second determining section, and the third determining section further determines any two phases of the first phase, the second phase, and the third phase. Determining whether or not an additional condition is satisfied that both the content ratios of the second harmonic contained in the differential current between the primary side and the secondary side are greater than the first set value;
6. A transformer protection relay as claimed in any one of claims 2 to 5, wherein said flip-flop is reset when said additional condition is not met. A relay that performs a current differential relay operation based on a fundamental wave component contained in a differential current between a primary side and a secondary side of the transformer for each of the first phase, the second phase, and the third phase of the transformer. a computing unit;
a determination unit that performs determination for detecting occurrence of an inrush current in the transformer, the determination unit comprising:
The second harmonic contained in the differential current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is higher than a first set value. A first condition of being large, and inclusion of a second harmonic included in the differential current between the primary side and the secondary side of any two of the first phase, the second phase, and the third phase. determining whether or not a second condition that both ratios are greater than a second set value is satisfied, wherein the second set value is smaller than the first set value;
The determination unit
When both the first condition and the second condition are satisfied, the output of the relay calculation unit is locked, and when the first condition is no longer satisfied or the second condition is no longer satisfied, the state is locked. A transformer protection relay that unlocks the output of the relay calculator if it continues for a set time of 1. Further comprising a dwell time measuring unit that measures a dwell time, which is the length of the flat portion of the inrush current waveform of the transformer,
The dwell time decreases according to the degree of deterioration of the iron core of the transformer,
8. The transformer protection relay according to claim 1 or 7, wherein said dwell time measuring section changes each set value compared with the harmonic content rate according to the amount of decrease in said dwell time. 8. The transformer protection relay according to claim 1 or 7 , wherein said relay operation unit determines presence/absence of an internal failure based on a ratio-differential principle. A transformer protection method using a protection relay, comprising:
A current differential relay operation is performed based on a fundamental wave component included in a differential current between the primary side and the secondary side of the transformer for each of the first phase, the second phase, and the third phase of the transformer. a step;
The second harmonic contained in the differential current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is higher than a first set value. a step of determining whether or not a first condition of being large is met;
It is determined whether or not a second condition that a second harmonic content included in the differential current between the primary side and the secondary side of the transformer is greater than a second set value is satisfied for each phase of the transformer. wherein the second set value is smaller than the first set value; and
A method for protecting a transformer, comprising the step of locking a protection relay output of a phase when the first condition is satisfied and the second condition is satisfied for a phase. The step of unlocking the protection relay output of the phase in which the protection relay output is locked when the state in which the second condition is not satisfied continues for a first set time. 11. The transformer protection method according to 10. For each phase of the transformer, the sum of the contents of the second harmonic, the third harmonic, and the fourth harmonic contained in the differential current between the primary side and the secondary side is the third a step of determining whether or not a third condition of being greater than the set value is met;
11. The transformer protection method of claim 10, further comprising unlocking the protection relay output of the phase in which the protection relay output is locked when the third condition is not met. . In the step of unlocking the protection relay output, if neither the second condition nor the third condition is satisfied in the phase in which the protection relay output is locked, the protection relay output of the phase is locked. 13. The transformer protection method of claim 12, wherein is released. a third set value for each of the phases of the transformer, wherein the sum of the contents of the second and fourth harmonics contained in the differential current between the primary side and the secondary side is greater than a third set value; a step of determining whether or not three conditions are met;
and unlocking the protection relay output of the phase in which the protection relay output is locked when neither the second condition nor the third condition is satisfied in the phase. Transformer protection method described in . The second harmonic contained in the differential current between the primary side and the secondary side of any two phases of the first phase, the second phase, and the third phase is equal to the first phase. Further comprising a step of determining whether or not an additional condition of being greater than the set value is established,
The transformer protection method according to any one of claims 11 to 14, wherein in the step of unlocking the protection relay output, the lock is unlocked when the additional condition is not satisfied. A transformer protection method using a protection relay, comprising:
A current differential relay operation is performed based on a fundamental wave component included in a differential current between the primary side and the secondary side of the transformer for each of the first phase, the second phase, and the third phase of the transformer. a step;
The second harmonic contained in the differential current between the primary side and the secondary side of any one of the first phase, the second phase, and the third phase is higher than a first set value. a step of determining whether or not a first condition of being large is met;
A content ratio of a second harmonic included in a difference current between the primary side and the secondary side of any two phases of the first phase, the second phase, and the third phase is set to a second setting. determining whether or not a second condition of being greater than the value is satisfied, wherein the second set value is smaller than the first set value;
locking the protection relay output of each phase when both the first condition and the second condition are satisfied;
unlocking the protection relay output when the first condition is no longer satisfied or when the second condition is no longer satisfied continues for a first set time. Further comprising the step of measuring a dwell time, which is the length of a flat portion in the inrush current waveform of the transformer, and changing each set value compared with the harmonic content according to the amount of decrease in the dwell time. ,
17. The transformer protection method according to claim 10 , wherein said dwell time decreases according to the degree of deterioration of said core of said transformer. 17. The transformer protection method according to claim 10 or 16 , wherein the step of performing the current-differential relay operation includes the step of determining presence/absence of an internal fault by a ratio-differential principle.

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