JP2016010223A - Current differential relay device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current differential relay device capable of preventing a malfunction caused by influences of electromagnetic induction in accordance with an inexpensive method.SOLUTION: In a current differential relay device 1, a ratio differential arithmetic operation section 17 performs ratio differential arithmetic operation on the basis of detection values of a primary current, a secondary current and a neutral point current of a transformer 4. A setting adjustment section 16 adjusts a setting K1 to be a determination reference for the presence/absence of an internal accident of the transformer 4 in the ratio differential arithmetic operation.A setting adjustment section 17 adjusts the setting K1 on the basis of comparing a first determination value ID with a second determination value IM. The first determination value ID is a magnitude of a zero-phase current calculated from the detection values of at least one of the primary current and the secondary current and the neutral point current. The second determination value IM is obtained by inverting a code of either the detection values of the primary and secondary currents or the detection value of the neutral point current and multiplying the neutral point current by a predetermined constant in calculating the first determination value.

Description

  The present invention relates to a current differential relay device for protecting a transformer or a bus provided in an electric power system.

  The protection relay device determines whether or not there is a failure in the area to be protected (protection section) of the power system, and when a failure is detected in the protection section, in order to disconnect the failure section from the system, Output the release command. Therefore, it is not allowed to malfunction when no failure occurs in the protection zone. Causes of malfunctions include lightning surges caused by lightning strikes on power systems, switching surges such as circuit breakers and disconnectors, and electromagnetic induction caused by large currents generated outside the protection section.

  The influence of electromagnetic induction becomes a problem when a protective relay device is housed in a metal box together with a circuit breaker or the like, such as a switchgear panel. In this case, since the primary electric wire of the power system is arranged in the vicinity of the protection relay device, a current of several tens of kA may flow through the primary electric wire, and the influence of electromagnetic induction cannot be ignored.

  Further, among the protective relay devices, the current differential relay is particularly susceptible to electromagnetic dielectrics. In the current differential relay, since all currents flowing into the protection section are detected and it is determined whether or not the sum is 0, even if the induced electromotive force superimposed on each detection signal is weak, each detection signal This is because the effect of the induced electromotive force may not be negligible when the values are added.

  In the conventional protection relay device, as a countermeasure against electromagnetic induction, a method using a magnetic shielding housing, a method of reducing a loop area of a wiring pattern on a printed circuit board, a secondary winding of an auxiliary transformer provided in an analog input unit Is divided into two or more windings, and a method of canceling the induced current by reversing the polarity of each of the divided windings has been proposed (for example, see Japanese Patent Application Laid-Open No. 2011-223873 (Patent Document 1)).

JP 2011-223873 A

  Of the above-described conventional techniques, the method using the magnetic shielding case and the method using the split secondary winding are likely to increase the cost because the hardware needs to be changed. Further, there is a problem that the housing becomes large when trying to perform complete magnetic shielding. The method of reducing the loop area of the wiring pattern on the circuit board cannot suppress the induced electromotive force generated in the auxiliary transformer that is particularly problematic.

  The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a current differential relay device capable of preventing malfunction due to the influence of electromagnetic induction by an inexpensive method. is there.

  The current differential relay device of the present invention includes an AD (Analog to Digital) converter, a ratio differential operation unit, and a settling value adjustment unit. The AD converter is a primary current that flows through the primary winding of the transformer, a secondary current that flows through the secondary winding of the transformer, and the neutral or primary and secondary windings of the primary or secondary winding. A / D conversion is performed for each detected value of the neutral point current flowing through the neutral point provided in common with the line. The ratio differential calculation unit performs a ratio differential calculation based on the detected values of the AD-converted primary current, secondary current, and neutral point current. The set value adjustment unit adjusts a set value that is a criterion for determining whether or not there is an internal fault in the transformer in the ratio differential operation. Here, the set value adjustment unit adjusts the set value based on a comparison between the first determination value and the second determination value. The first determination value is the magnitude of the difference current of the zero-phase circuit calculated from the detected value of the current flowing through the winding having the neutral point of the primary current and the secondary current and the detected value of the neutral point current. That's it. The second determination value is obtained by inverting the sign of one of the detection values of the primary and secondary currents and the detection value of the neutral point current in the calculation of the first determination value. This is a value obtained by multiplying the detection value by a predetermined constant.

  According to the present invention, the presence / absence of an accident can be determined with high sensitivity only at the time of an internal accident by adjusting the settling value based on comparison with the first and second determination values. As a result, malfunction caused by electromagnetic induction can be prevented without changing hardware.

It is a block diagram which shows the structure of the current differential relay apparatus by 1st Embodiment. It is a figure for demonstrating the influence of the electromagnetic induction with respect to a current differential relay apparatus. It is a flowchart which shows operation | movement of the digital signal processing part of FIG. It is a block diagram which shows operation | movement of a set value control part. It is a figure which shows the relationship between the 2nd difference electric current and suppression current, and the parameter m in the case of an internal ground fault. It is a block diagram which shows the structure of the current differential relay apparatus by 2nd Embodiment. It is a flowchart which shows operation | movement of the digital signal processing part of FIG. It is a block diagram which shows the structure of the current differential relay apparatus by 3rd Embodiment. It is a flowchart which shows operation | movement of the digital signal processing part of FIG.

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

<First Embodiment>
[Configuration of current differential relay device]
FIG. 1 is a block diagram showing the configuration of the current differential relay device according to the first embodiment. Referring to FIG. 1, a current differential relay device 1 protects a Y-Δ connection type three-phase transformer 4 in which a primary side is a Y winding and a secondary side is a Δ winding. Current transformers 5 A, 5 B, 5 C are provided on the primary side of the transformer 4, and current transformers 6 A, 6 B, 6 C are provided on the secondary side of the transformer 4. Furthermore, a current transformer 7 is provided on the ground line that connects between the neutral point NP of the primary winding of the transformer 4 and the ground pole GND. The primary currents Ia1, 1b1, Ic flowing through the primary windings detected by these current transformers, the secondary currents Ia2, Ib2, Ic2 flowing through the secondary windings, and the neutral points of the primary windings flow. A signal representing the neutral point current IN is taken into the current differential relay device 1.

  The current differential relay device 1 is a digital protection relay device configured based on a microcomputer. As shown in FIG. 1, the current differential relay device 1 includes an input conversion block 2, an analog circuit 11, a filter processing unit 12, a correction processing unit 13, a first difference current / suppression current calculation unit 14, and , A second difference current / suppression current calculation unit 15, a settling value control unit 16, a ratio differential calculation unit 17, a failure determination unit 18, and an output circuit 19.

  The input conversion block 2 includes a plurality of auxiliary transformers (reference numeral 3 in FIG. 2) corresponding to the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7, respectively. The secondary voltage signal of the corresponding current transformer is converted into a voltage signal having a magnitude suitable for the current differential relay device 1 by the auxiliary transformer.

  The analog circuit 11 includes an analog filter (not shown), a sample hold circuit, an AD (Analog to Digital) converter, and the like. The analog filter is a low-pass filter for removing aliasing errors during AD conversion. The sample hold circuit is provided corresponding to each of voltage signals representing the primary current, secondary current, and neutral point current of the transformer, and samples and holds the corresponding voltage signal. The AD converter AD converts the signal held in the sample hold circuit. The AD-converted digital data is taken into a microcomputer.

  Filter processing unit 12, correction processing unit, first difference current / suppression current calculation unit 14, second difference current / suppression current calculation unit 15, settling value control unit 16, ratio differential calculation unit 17, and failure determination unit 18 is realized by software processing by a CPU (Central Processing Unit). Hereinafter, these components 12 to 18 are collectively referred to as a digital signal processing unit 21.

  The digital signal processing unit 21 performs a relay calculation based on the digital signal output from the analog circuit 11, and determines whether there is a failure in the transformer 4 to be protected based on the result of the relay calculation. Detailed functions of the constituent elements 12 to 18 constituting the digital signal processing unit 21 will be described later with reference to the flowchart of FIG.

  Based on the determination result of the digital signal processing unit 21, the output circuit 19 outputs an open signal 20 to a circuit breaker (not shown) in order to disconnect the transformer 4 from the power system in the case of an internal failure of the transformer 4. Output. The circuit breaker is usually installed on the side closer to the transformer 4 than the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7. The transformer 4 is disconnected from the power system by opening the circuit breaker.

[Influence of electromagnetic induction]
FIG. 2 is a diagram for explaining the influence of electromagnetic induction on the current differential relay device.

  Referring to FIG. 2, current differential relay device 1 is affected by a magnetic field (line of magnetic force ML) generated by a nearby power line. The direction of the magnetic field (lines of magnetic force ML) varies depending on the arrangement of nearby power lines. For example, as shown in FIG. 2A, in the up-down direction (Z direction), as shown in FIG. 2B, in the left-right direction (Y direction), and as shown in FIG. 2C, in the front-back direction (X direction). Magnetic field lines ML can occur. It is necessary for the current differential relay device 1 not to malfunction due to the induced electromotive force no matter which direction the magnetic field is applied.

  The current differential relay device 1 is usually built in a housing such as a metal case. The input conversion block 2, the analog circuit 11, the digital signal processing unit 21, and the output circuit 19 described in FIG. Of these, the auxiliary transformer 3 provided in the input conversion block 2 is particularly susceptible to electromagnetic induction.

  When there is no influence of electromagnetic induction, signals from the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7 are correctly converted by the auxiliary transformer 3. On the other hand, when there is an influence of electromagnetic induction, an induced electromotive force is superimposed on signals from the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7. Here, in a normal current differential relay device, an auxiliary transformer having the same specification is used for all input signals. Therefore, if the magnetic field lines ML penetrate the auxiliary transformers 3 equally, the auxiliary electromotive force of the same magnitude is generated in the auxiliary transformers 3. This dielectric electromotive force causes a malfunction of the current differential relay device 1.

[Operation of current differential relay device]
FIG. 3 is a flowchart showing the operation of the digital signal processing unit of FIG. Hereinafter, the operation of the digital signal processing unit 21 will be further described with reference to FIGS. 1 and 3.

  First, the filter processing unit 12 performs filter processing necessary for transformer protection on the data after AD conversion. The sampling rate at the time of AD conversion is, for example, 96 × fn (fn is the rated frequency of the power system), but the sampling rate is 12 × fn or 16 × fn as a result of filtering by the filter processing unit 12. Converted. In the case of 12 × fn, the transformer primary currents Ia1, Ib1, Ic1, secondary currents Ia2, Ib2, Ic2, and neutral point current IN are obtained every 30 degrees of the rated frequency (step S100).

  The correction processing unit 13 performs phase correction and gain correction. In the phase correction, the primary phase and the secondary phase of the transformer 4 are matched. In the case of Y-Δ connection, the phase can be matched by performing Δ operation on the primary currents Ia1, Ib1, and Ic1. Note that the Δ calculation refers to a process for obtaining a difference between phases such as (Ia1-Ib1), (Ib1-Ic1), and (Ic1-Ia1).

  In the gain correction, based on the transformation ratio of the transformer 4 and the transformation ratios of the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7, the load differential is used in the differential ratio calculation when the load current normally flows through the transformer. The gain is corrected so that the difference current becomes zero. In the following, for the sake of simplicity, it is assumed that the transformation ratios of the current transformers 5A, 5B, 5C, 6A, 6B, 6C, and 7 are set so as to correct the transformation ratio of the transformer 4.

The ratio differential operation can be divided into protection of the transformer 4 and protection of the Y winding. First, transformer protection will be described. The calculation unit 14 calculates the difference currents IDa, IDb, IDc used for the ratio differential calculation,
IDa = | (Ia1-Ib1) + Ia2 | (1)
IDb = | (Ib1-Ic1) + Ib2 | (2)
IDc = | (Ic1-Ia1) + Ic2 | (3)
(Step S105). In the above formula, the symbol || represents the effective value. Instead of the effective value, an amplitude value may be used for the calculation. In this specification, the effective value and the amplitude value may be collectively referred to as a magnitude.

The calculation unit 14 further supplies the suppression currents IRa, IRb, IRg used for the ratio differential calculation,
IRa = max (| Ia1-Ib1 |, | Ia2 |) (4)
IRb = max (| Ib1-Ic1 |, | Ib2 |) (5)
IRc = max (| Ic1-Ia1 |, | Ic2 |) (6)
(Step S110). In the above equation, the function max represents the maximum of the arguments. Instead of the maximum effective value, a scalar sum may be used as the suppression current.

The ratio differential operation unit 17
IDa> K2 (7)
IDa> P2 · IRa (8)
Whether or not is satisfied is determined (step S145). Failure determination unit 18 determines that there is a failure (short-circuit failure, ground fault) inside the transformer when both of the above expressions (7) and (8) are satisfied (step S150). In the above equations (7) and (8), K2 and P2 are constants. Similar determinations are made for IDb, IRb, IDc, and IRc.

  In the above calculation, since the primary current of the transformer 4 is differentiated as in Ia1-Ib1, the error due to electromagnetic induction is cancelled. Therefore, in the calculation of the difference currents IDa, IDb, and IDc, only the dielectric electromotive force superimposed on one auxiliary transformer becomes an error, so that the influence of electromagnetic induction can be ignored.

Next, protection of the Y winding will be described. The calculation unit 14 calculates a difference current IDg (hereinafter also referred to as a first difference current) used for ratio differential calculation for Y winding protection.
IDg = | Ia1 + Ib1 + Ic1 + IN | (9)
(Step S105). That is, the primary currents Ia1, Ib1, Ic1 flowing through the three-phase wires connected to the Y winding are added to the neutral point current IN, and the effective value of the addition result is calculated as the difference current IDg (primary current And the polarity of the neutral point current are selected so that the above-mentioned addition result becomes 0 when normal or when an external ground fault occurs).

The calculation unit 14 further uses a suppression current IRg (hereinafter also referred to as a first suppression current) used for ratio differential calculation for Y winding protection.
IRg = max (| Ia1 |, | Ib1 |, | Ic1 |, | IN |) (10)
(Step S110). Note that a scalar sum may be used as the suppression current instead of the maximum effective value.

The ratio differential operation unit 17
IDg> K1 (11)
IDg> P1 · IRg (12)
Whether or not is satisfied is determined (step S135). The failure determination unit 18 determines that there is a ground fault in the Y winding when both the above equations (11) and (12) are satisfied (step S140). In the above formulas (11) and (12), K1 and P1 are constants.

In the calculation of the difference current IDg, the induced electromotive force generated in the four auxiliary transformers is added, so that the error due to electromagnetic induction can be at a level that cannot be ignored. Specifically, assuming that an error of one auxiliary transformer due to electromagnetic induction is Ie, a difference current IDg (hereinafter referred to as difference current IDge) considering an error due to electromagnetic induction is:
IDge = | (Ia1 + Ie) + (Ib1 + Ie) + (Ic1 + Ie) + (IN + Ie) |
= | Ia1 + Ib1 + Ic1 + IN + 4 · Ie | = | Dg + 4 · Ie | (13)
It is represented by

  If 4 · Ie in the above equation (13) exceeds the operating sensitivity of the current differential relay, there is a possibility of malfunction. Therefore, the calculation unit 15 calculates a second difference current ID (also referred to as a first determination value) and a second suppression current IM (also referred to as a second determination value) as described below (step S115, S120). The set value control unit 16 determines whether or not the set value K1 should be changed based on the calculated second difference current ID and the second suppression current IM (step S125). Specifically, if the set value control unit 16 determines that there is an error due to electromagnetic induction rather than a ground fault in the transformer (YES in step S125), the set value K1 is set to K1 + KM (where KM> 4Ie). (Step S130). As a result, malfunction of the current differential relay element for protecting the Y winding can be prevented. Hereinafter, operations of the calculation unit 15 and the set value control unit 16 will be described in more detail.

[Control of settling value of differential ratio calculation]
Since the above equation (9) is the difference current of the zero phase circuit, there is no influence of the load current. Therefore, the calculating part 15 calculates 2nd difference current ID using the above-mentioned Formula (9). That is, ID = IDg. When the error Ie due to electromagnetic induction is taken into consideration, the second difference current ID is given by IDge in Expression (13).

The calculation unit 15 further sets the second suppression current IM so as to cancel the influence of electromagnetic induction.
IM = | Ia1 + Ie + Ib1 + Ie + Ic1 + Ie−3 · (IN + Ie) |
= | (Ia1 + Ib1 + Ic1) −3 · IN | (14)
Calculate according to Specifically, in the calculation of the second difference current ID, one of the primary currents Ia1, Ib1, Ic1 and the neutral point current IN is inverted (in the above equation, the neutral point current IN The second suppression current IM is obtained by multiplying the neutral point current IN by a predetermined constant multiple (in this example, three times). The second suppression current IM given by the above equation (14) becomes 0 regardless of the presence or absence of the influence of electromagnetic induction at the normal time when the load current flows.

  Hereinafter, how the values of the second differential current ID and the second suppression current IM change according to the state of the power system will be described. The determination method of whether the set value control part 16 changes the set value K1 is based on the following calculation results.

(I) In the case of normal load, external short-circuit fault, two-phase and three-phase short-circuit fault inside the transformer Since Ia1 + Ib1 + Ic1 = IN = 0, the second differential current ID and the second suppression current IM are
ID = | Ia1 + Ib1 + Ic + IN + 4 · Ie | = | 4 · Ie | (15)
IM == | (Ia1 + Ib1 + Ic1) -3IN | = 0 (16)
Given in.

(Ii) Case of external 1-phase ground fault and external 2-phase ground fault Assume that a ground fault has occurred on the primary side of the transformer 4. If the ground fault current is If, since Ia1 + Ib1 + Ic1 = −IN = If, the second difference current ID and the second suppression current IM are
ID = | Ia1 + Ib1 + Ic1 + IN + 4Ie | = | 4Ie | (17)
IM = | (Ia1 + Ib1 + Ic1) −3IN | = | 4If | (18)
Given in.

(Iii) In the case of an internal one-phase ground fault and an internal two-phase ground fault If the ground fault occurs in the Y winding, the relationship of Ia1 + Ib1 + Ic1 = If is established using the ground fault current If. In this case, since the neutral point current IN is expressed as IN = m × If (where 0 ≦ m ≦ 1), the second difference current ID and the second suppression current IM are
ID = | Ia1 + Ib1 + Ic1 + IN + 4Ie |
= | (1 + m) If + 4 · Ie | (19)
IM = | (Ia1 + Ib1 + Ic1) -3IN |
= | (1-3m) If | (20)
Given in.

  FIG. 4 is a block diagram illustrating the operation of the set value control unit. Referring to FIG. 4, settling value control unit 16 includes a determination unit 30, AND circuits 31 and 32, an OR circuit 33, and a settling value setting unit 34.

The determination unit 30 determines the relationship between the second differential current ID and the second suppression current IM and the constants M1, M2, M3, M4, and Q.
M1>ID> M2 (21A)
IM <M3 (21B)
IM> ID / Q (21C)
IM-ID> M4 (21D)
It is determined whether the expressions (21A) to (21D) expressed by the following are established.

However, the constants M1 and M2 are
M1> 4Ie + M2 (22)
M2> (Error in load current state (error of current transformer, etc.)) ... (23)
Is set to satisfy the relationship.

The constants M3, M4 and Q are
M3> 3 phase equilibrium error, and M3 <4If (24)
M4> 4Ie + M2 (25)
Q> 1+ (4Ie / If) (26)
Is set to satisfy the relationship. Normally, the three-phase equilibrium error is smaller than the fault current, so the condition of M3 <4 · If is not particularly required.

  When the above equations (21A) and (21B) are both established, the output 35 of the AND circuit 31 is “1”. In this case, a normal load state or a short circuit failure state is indicated.

  When the above equations (21A), (21C), and (21D) are all established, the output 36 of the AND circuit 32 becomes “1”. In this case, an external one-phase ground fault condition or an external two-phase ground fault condition is shown.

In the case of an internal ground fault, the above formulas (19) and (20) are satisfied, and further, when 0 ≦ m ≦ 1, 1 ≦ (1 + m) / | 1-3m |
ID / IM = | (1 + m) / (1-3m) + 4 · Ie / If |
≧ | 1 + 4 · Ie / If | (27)
(Equal signs hold when m = 0 and 1). Therefore, when it is not an internal ground fault, the above formula (21C) is established. Note that since If> Ie, the constant Q is determined in consideration of this condition.

  However, when the amount of current is small, an error may occur only by the relationship of equation (21C), and therefore equation (21D) is also added as a determination equation in the case of no internal ground fault.

  FIG. 5 is a diagram illustrating the relationship between the second differential current and suppression current and the parameter m in the case of an internal ground fault. The horizontal axis in FIG. 5 indicates the parameter m in the equations (19) and (20), and the vertical axis in FIG. 5 indicates the magnitude of the second differential current ID and the second suppression current IM. As shown in FIG. 5, since ID ≧ IM + 4 · Ie is satisfied in the range of 0 ≦ m ≦ 1, the above equation (21D) is satisfied when there is no internal ground fault.

  Referring to FIG. 4 again, OR circuit 33 outputs “1” when the output of either AND circuit 31 or 32 is “1”. When the output of the OR circuit 33 is “1”, the set value setting unit 34 increases the set value K1 of the ratio differential calculation to K1 + KM (where KM> 4 · Ie). The control signal from the set value setting unit 34 is input to the ratio differential calculation unit 17 and the operation sensitivity of the ratio differential relay is changed. As a result, there is no output of the OR circuit 33 in the case of an internal failure, so there is no problem of reduced relay sensitivity due to the internal failure, and unnecessary operation due to electromagnetic induction of the current differential relay device is performed in a normal state or an external failure state. Can be prevented.

[Effect of the first embodiment]
As described above, according to the current differential relay device of the first embodiment, even if the induced electromotive force is uniformly superimposed on the output voltage of the auxiliary transformer, unnecessary operation can be prevented. This is an inexpensive method because only software processing is performed without changing hardware.

  In the above description, the case of Y winding protection in the case of a Y-Δ connection transformer has been described as an example. However, in the case of Y winding protection of Δ-Y connection and YY connection, the same method is used. Unnecessary operations due to electromagnetic induction can be prevented.

  In the determination of a short-circuit fault in the case of a transformer with Y-Y connection, the error due to electromagnetic induction is canceled by performing Δ operation on both the primary current and secondary current of the transformer. be able to. When judging short-circuit faults and ground faults in transformers with Δ-Δ connections, errors due to electromagnetic induction are canceled by applying Δ-Y conversion to the primary current and secondary current, respectively. it can. Therefore, in any case, the control of the settling value K1 as described above is not particularly required.

<Second Embodiment>
In the second embodiment, a case where an auto-transformer (single-winding transformer) is protected by a current differential relay device will be described.

  FIG. 6 is a block diagram showing the configuration of the current differential relay device according to the second embodiment. In the current differential relay device 1A of FIG. 6, the same reference numerals are assigned to the portions corresponding to the current differential relay device 1 of FIG.

  FIG. 7 is a flowchart showing the operation of the digital signal processing unit of FIG. In FIG. 6, steps corresponding to those in FIG. 3 are denoted by the same reference numerals.

  Referring to FIGS. 6 and 7, current differential relay device 1 </ b> A is used for protection of auto transformer 8. In the auto transformer 8, the secondary-side electric wire branches off from the branch point corresponding to the transformation ratio of each winding. As shown in FIG. 6, current transformers 5 </ b> A, 5 </ b> B, 5 </ b> C are provided on the primary side of the transformer 8, and current transformers 6 </ b> A, 6 </ b> B, 6 </ b> C are provided on the secondary side of the transformer 8. Furthermore, current transformers 7A, 7B, and 7C are provided on the neutral point NP side of each winding of the transformer 8. Therefore, current transformers 5A and 7A are provided at both ends of the A-phase winding, current transformers 5B and 7B are provided at both ends of the B-phase winding, and current transformers 5C and 7C are provided at both ends of the C-phase winding. Provided.

  Since operations of input conversion block 2 and analog circuit 11 are the same as those in the first embodiment, description thereof will not be repeated. The digital signal processing unit 21 includes primary currents Ia1, 1b1, Ic1 flowing through the primary winding of the transformer, secondary currents Ia2, Ib2, Ic2 flowing through the secondary winding of the transformer, and primary and secondary Digital signals representing neutral point currents Ian, Ibn, and Icn flowing through neutral points common to the windings are captured (step S100). The filter processing unit 12 performs the same filter processing as in the first embodiment.

In the transformer protection in the second embodiment, differential protection is performed for each of A, B, and C phases. The calculation unit 14 calculates the difference currents IDa, IDb, IDc used for the ratio differential calculation,
IDa = | Ia1 + Ia2 + Ian | (28)
IDb = | Ib1 + Ib2 + Ibn | (29)
IDc = | Ic1 + Ic2 + Icn | (30)
(Step S105).

The calculation unit 14 further supplies the suppression currents IRa, IRb, IRg used for the ratio differential calculation,
IRa = max (| Ia1 |, | Ia2 |, | Ian |) (31)
IRb = max (| Ib1 |, | Ib2 |, | Ibn |) (32)
IRc = max (| Ic1 |, | Ic2 |, | Icn |) (33)
(Step S110). Instead of the maximum effective value, a scalar sum may be used as the suppression current.

The ratio differential operation unit 17
IDa> K1 (34)
IDa> P1 · IRa (35)
Whether or not is satisfied is determined (step S135). Failure determination unit 18 determines that there is a failure (short-circuit failure, ground fault) in the transformer when both of the above equations (34) and (35) are satisfied (step S140). In the above formulas (34) and (35), K1 and P1 are constants. Similar determinations are made for IDb, IRb, IDc, and IRc.

In the above calculation of the difference currents IDa, IDb, IDc, the induced electromotive force generated in the three auxiliary transformers is added, so that the error due to electromagnetic induction can be at a level that cannot be ignored. Assuming that the error of one auxiliary transformer due to electromagnetic induction is Ie, the difference currents IDa, IDb, IDc (hereinafter referred to as IDae, IDbe, IDce) considering the error due to electromagnetic induction are:
IDae = | (Ia1 + Ie) + (Ia2 + Ie) + (Ian + Ie) |
= | IDa + 3 · Ie | (36)
IDbe = | (Ib1 + Ie) + (Ib2 + Ie) + (Ibn + Ie) |
= | IDb + 3 · Ie | (37)
IDce = | (Ic1 + Ie) + (Ibc + Ie) + (Icn + Ie) |
= | IDc + 3 · Ie | (38)
It is represented by

If 3 · Ie in the above equation exceeds the operating sensitivity of the current differential relay, it may malfunction. Therefore, the calculation unit 15
ID = | IDa + IDb + IDc | (39)
IM = | Ia1 + Ib1 + Ic1 + Ia2 + Ib2 + Ic2-2− (Ian + Ibn + Icn) | (40)
Is calculated (step S115, S120).

  The second difference current ID is a difference current of a zero-phase current synthesized in three phases in order to eliminate the influence of the load current. That is, the second difference current ID is obtained by adding the primary currents Ia1, Ib1, and Ic1, the secondary currents Ia2, Ib2, and Ic2, and the neutral point currents Ian, Ibn, and Icn, and obtaining an effective value of the addition result. (The polarity of the primary current, the polarity of the secondary current, and the polarity of the neutral point current are selected so that the above-mentioned addition result becomes 0 at the time of normal or an external ground fault).

  The second suppression current IM is determined to be the same value regardless of the presence or absence of electromagnetic induction. Specifically, the second suppression current IM is calculated from the primary and secondary currents Ia1, Ib1, Ic1, Ia2, Ib2, Ic2 and the neutral point currents Ian, Ibn, Icn in the calculation of the second differential current ID. Invert the sign of one of them (in the above formula, the sign of the neutral point current is inverted) and multiply each neutral point current Ian, Ibn, Icn by a predetermined constant (in this example, double). Obtained by.

Considering the error Ie, the second difference current ID is
ID = | IDa + IDb + IDc + 9 · Ie | (41)
It is transformed as follows. Since the error amount is canceled, the second suppression current IM has the same value when the error amount is considered and when it is not considered.

  Hereinafter, how the values of the second differential current ID and the second suppression current IM change according to the state of the power system will be described. The determination method as to whether or not the set value control unit 16 changes the set value K1 is based on the following calculation result.

(I) In the case of an external short-circuit fault, a two-phase and a three-phase short-circuit fault inside the transformer at normal load Ia1 + Ib1 + Ic1 = Ia2 + Ib2 + Ic2 = Ian + Ibn + Icn = 0
ID = | 9 · Ie | (42)
IM = 0 (43)
Given in.

(Ii) In the case of an external one-phase ground fault It is assumed that an external ground fault has occurred in the phase A on the primary side of the transformer 8. If the ground fault current is If, then Ia1 + Ia2 = −Ian = If and Ib1 + Ib2 = Ibn = Ic1 + Ic2 = Icn = 0, the second difference current ID and the second suppression current IM are
ID = | 9 · Ie | (44)
IM = | 3 · If | (45)
Given in.

(Iii) In the case of an external two-phase ground fault It is assumed that an external ground fault has occurred in the A phase and the B phase on the primary side of the transformer 8. If the ground fault current is If, then Ia1 + Ia2 + Ib1 + Ib2 = − (Ian + Ibn) = If and Ic1 + Ic2 = Icn = 0, the second differential current ID and the second suppression current IM are
ID = | 9 · Ie | (46)
IM = | 3 · If | (47)
Given in.

(Iv) In the case of an internal one-phase ground fault It is assumed that an internal ground fault has occurred in the phase A on the primary side of the transformer 8. If the ground fault current is If, then Ia1 + Ia2 = If, Ian = m × If (where 0 ≦ m ≦ 1), Ib1 + Ib2 = Ibn = Ic1 + Ic2 = Icn = 0, so that the second difference current ID and the second The suppression current IM of 2 is
ID = | (1 + m) · If + 9 · Ie | (48)
IM = | (1-2m) · If | (49)
Given in.

(V) In the case of an internal two-phase ground fault It is assumed that an internal ground fault has occurred in the A phase and B phase on the primary side of the transformer 8. If the ground fault current is If, Ia1 + Ia2 + Ib1 + Ib2 = If, Ian + Ibn = m × If (where 0 ≦ m ≦ 1), Ic1 + Ic2 = Icn = 0, so that the second difference current ID and the second suppression current IM is
ID = | (1 + m) · If + 9 · Ie | (50)
IM = | (1-2m) · If | (51)
Given in.

  Next, the operation of the set value control unit 16 will be described. The operation of the set value control unit 16 is basically represented by the block diagram of FIG. That is, the set value control unit 16 includes a determination unit 30, AND circuits 31 and 32, an OR circuit 33, and a set value setting unit 34.

The determination unit 30 determines the relationship between the second differential current ID and the second suppression current IM and the constants M1, M2, M3, M4, and Q.
M1>ID> M2 (52A)
IM <M3 (52B)
IM> ID / Q (52C)
IM-ID> M4 (52D)
It is determined whether each expression represented by is established.

The constants M1, M2, M3, M4 and Q are
M1> 9Ie + M2 (53)
M2> (error in load current state (error of current transformer, etc.)) (54)
M3> 3 phase equilibrium error, and M3 <3If (55)
M4> 9Ie + M2 (56)
Q> 1+ (9Ie / If) (57)
It is set so as to satisfy each relational expression represented by. Normally, the three-phase equilibrium error is smaller than the fault current, so the condition of M3 <3 · If in the above equation (55) need not be considered.

  When both the above equations (52A) and (52B) hold, the output 35 of the AND circuit 31 is “1”. In this case, a normal load state or a short circuit failure state is indicated.

  When the above equations (52A), (52C), and (52D) are all established, the output 36 of the AND circuit 32 becomes “1”. In this case, an external one-phase ground fault condition or an external two-phase ground fault condition is shown.

In the case of an internal ground fault, the above formulas (48) to (51) are satisfied, and further, when 0 ≦ m ≦ 1, 1 ≦ (1 + m) / | 1-2m |
ID / IM = | (1 + m) / (1-2m) + 9 · Ie / If |
≧ | 1 + 9 Ie / If | (58)
(Equal signs hold when m = 0). Therefore, when it is not an internal ground fault, the above formula (52C) is established.

  The OR circuit 33 outputs “1” when the output of either of the AND circuits 31 and 32 is “1”. When the output of the OR circuit 33 is “1”, the set value setting unit 34 increases the set value K1 of the ratio differential calculation to K1 + KM (where KM> 9 · Ie). The control signal from the set value setting unit 34 is input to the ratio differential calculation unit 17 and the operation sensitivity of the ratio differential relay is changed. As a result, there is no output of the OR circuit 33 in the case of an internal failure, so there is no problem of reduced relay sensitivity due to the internal failure, and unnecessary operation due to electromagnetic induction of the current differential relay device is performed in a normal state or an external failure state. Can be prevented.

  The reason why the three-phase current is combined for the second difference current ID and the second suppression current IM is that the second suppression current IM is set to 0 (actually, the balance error of the three phases) for the normal load current. This is because the conditional expression (52B) can be applied and the determination logic is simplified.

<Third Embodiment>
In the third embodiment, a case where bus protection is performed by a current differential relay device will be described.

  FIG. 8 is a block diagram showing the configuration of the current differential relay device according to the third embodiment. In the current differential relay device 1B of FIG. 8, the same reference numerals are assigned to the portions corresponding to the current differential relay 1 of FIG.

  FIG. 9 is a flowchart showing the operation of the digital signal processing unit of FIG. In FIG. 9, steps corresponding to those in FIG. 3 are denoted by the same reference numerals.

  8 and 9, n feeder lines 41-1 to 41-n are branched from bus 40. The feeder lines 41-1 to 41-n are provided with current transformers 42-1 to 42-n, respectively.

  Since operations of input conversion block 2 and analog circuit 11 are the same as those in the first embodiment, description thereof will not be repeated. The digital signal processing unit 21 receives the three-phase currents (Ia1, Ib1, Ic1) to (Ian, Ibn, Icn) flowing through the feeder lines (step S100). The filter processing unit 12 performs the same filter processing as in the first embodiment.

In the bus bar protection according to the third embodiment, differential protection is performed for each of A, B, and C phases. The calculation unit 14 calculates the difference currents IDa, IDb, IDc used for the ratio differential calculation,
IDa = | Ia1 + Ia2 + ... + Ian | (59)
IDb = | Ib1 + Ib2 +... + Ibn | (60)
IDc = | Ic1 + Ic2 + ... + Icn | (61)
(Step S105).

The calculation unit 14 further supplies the suppression currents IRa, IRb, IRg used for the ratio differential calculation,
IRa = max (| Ia1 |, | Ia2 |,..., | Ian |) (62)
IRb = max (| Ib1 |, | Ib2 |,..., | Ibn |) (63)
IRc = max (| Ic1 |, | Ic2 |,..., | Icn |) (64)
(Step S110). Instead of the maximum effective value, a scalar sum may be used as the suppression current.

The ratio differential operation unit 17
IDa> K1 (65)
IDa> P1 · IRa (66)
Whether or not is satisfied is determined (step S135). Failure determination unit 18 determines that there is a failure (short circuit failure, ground fault) inside the bus when both of the above expressions (65) and (66) are satisfied (step S140). In the above formulas (65) and (66), K1 and P1 are constants. Similar determinations are made for IDb, IRb, IDc, and IRc.

In the calculation of the difference currents IDa, IDb, and IDc, the induced electromotive force generated in the n auxiliary transformers is added, so that the error due to electromagnetic induction can be at a level that cannot be ignored. Assuming that the error of one auxiliary transformer due to electromagnetic induction is Ie, the difference currents IDa, IDb, IDc (hereinafter referred to as IDae, IDbe, IDce) considering the error due to electromagnetic induction are:
IDae = | (Ia1 + Ie) + (Ia2 + Ie) +... + (Ian + Ie) |
= | IDa + n · Ie | (67)
IDbe = | (Ib1 + Ie) + (Ib2 + Ie) +... + (Ibn + Ie) |
= | IDb + n · Ie | (68)
IDce = | (Ic1 + Ie) + (Ibc + Ie) +... + (Icn + Ie) |
= | IDc + n · Ie | (69)
It is represented by

If n · Ie in the above equation exceeds the operating sensitivity of the current differential relay, it may malfunction. Therefore, the calculation unit 15 calculates the second difference current ID and the second suppression current IM as
ID = | IDa + IDb + IDc | (70)
IM = | (Ia1 + Ib1 + Ic1) − (Ia2 + Ib2 + Ic2) + (Ia3 + Ib3 + Ic3) −… |… (71)
(Steps S115 and S120).

  In the above equations (70) and (71), the second difference current ID is the magnitude of the difference current of the zero-phase circuit. That is, the second difference current ID is calculated by adding the three-phase currents that respectively flow through the n feeder lines and obtaining the effective value of the addition result (the polarity of the three-phase current of each feeder line is normal) The above addition result is selected to be 0 at the time of an external fault or an external ground fault).

  The second suppression current IM is obtained by adding (or subtracting) the three-phase combined current in the odd-numbered feeder line of the n feeder lines and calculating the three-phase combined current in the even-numbered feeder line. It is calculated by subtracting (or adding) and obtaining the effective value of the addition / subtraction result. In other words, in the calculation of the second difference current ID, the second suppression current IM is one of the sign of the current flowing through the odd-numbered order feeder line and the current flowing through the even-numbered order feeder line. Is a value obtained by inverting.

In consideration of the electromagnetic induction error Ie, the second difference current ID is
ID = | IDa + IDb + IDc + 3n · Ie | (72)
It is expressed.

  The second suppression current IM is determined to be substantially the same value regardless of the presence or absence of electromagnetic induction. That is, when the number of feeder lines is an even number, the error due to electromagnetic induction is canceled. When the number of feeder lines is an odd number, an error Ie for one auxiliary transformer remains, but this is not a problem because it is a negligible level. In addition, the result of a short circuit failure becomes the same result as a load state by using 3 phase composition, and it can simplify.

  Hereinafter, how the values of the second differential current ID and the second suppression current IM change according to the state of the power system will be described. The determination method of whether the set value control part 16 changes the set value K1 is based on the following calculation results.

(I) In the case of normal load, external short-circuit fault, two-phase and three-phase short-circuit fault inside the transformer Since Ia1 + Ib1 + Ic1 =... = Ian + Ibn + Icn = 0, the second differential current ID and the second suppression current IM are
ID = | 3n · Ie | (73)
IM = 0 (74)
Given in.

(Ii) In the case of an external 1-phase ground fault and an external 2-phase ground fault An external ground fault occurs in the A phase of the feeder line 41-1, and the current of the other feeder lines 41-2 to 41-n is Suppose that it flows into the ground fault point of A phase of -1. If the ground fault current is If, Ia1 = − (Ia2 + Ia3 +... + Ian) = If, the second difference current ID and the second suppression current IM are
ID = | 3n · Ie | (75)
IM = | m1 × If | (76)
Given in. In addition, although m1 changes with system | strain structures, it is 2> = m1> = 0.

(Iii) In the case of an internal one-phase ground fault or an internal two-phase ground fault An internal ground fault occurs in the A phase of the feeder line 41-1, and the current of the other feeder lines 41-2 to 41-n is Suppose that it flows into the ground fault point of A phase of -1. If the ground fault current is If, Ia1 + Ia2 + Ia3 +... + Ian = If, the second difference current ID and the second suppression current IM are
ID = | If + 3n · Ie | (77)
IM = | m2 × If | (78)
Given in. Although m2 varies depending on the system configuration, 1 ≧ m2 ≧ 0.

  Next, the operation of the set value control unit 16 will be described. The operation of the set value control unit 16 is basically represented by the block diagram of FIG. That is, the set value control unit 16 includes a determination unit 30, AND circuits 31 and 32, an OR circuit 33, and a set value setting unit 34.

The determination unit 30 determines the relationship between the second differential current ID and the second suppression current IM and the constants M1, M2, M3, M4, and Q.
M1>ID> M2 (79A)
IM <M3 (79B)
IM> ID / Q (79C)
IM-ID> M4 (79D)
It is determined whether each expression expressed by

The constants M1, M2, M3, M4 and Q are
M1> 3n · Ie + M2 (80)
M2> (Error in load current state (error of current transformer, etc.)) ... (81)
M3> 3 phase balance error, and M3 <m1 × If (82)
M4> 3n · Ie + M2 (83)
Q> 1+ (3n · Ie / If) (84)
It is set so as to satisfy each relational expression represented by. Usually, If> Ie, each constant is set in consideration of this. Since the three-phase balance error is smaller than the fault current, the condition of M3 <m1 × If in the above equation (82) may not be considered.

  When both the above equations (79A) and (79B) hold, the output 35 of the AND circuit 31 becomes “1”. In this case, a normal load state or a short circuit failure state is indicated.

  When the above equations (79A), (79C), and (79D) are all established, the output 36 of the AND circuit 32 is “1”. In this case, an external one-phase ground fault condition or an external two-phase ground fault condition is shown.

In the case of an internal ground fault, since the above equations (77) and (78) are satisfied, and further 0 ≦ m2 ≦ 1,
ID / IM = | 1 / m2 + 3n · Ie / If |
≧ | 1 + 3n · Ie / If | (85)
(Equal signs hold when m2 = 1). Therefore, when it is not an internal ground fault, the above formula (79C) is established.

  The OR circuit 33 outputs “1” when the output of either of the AND circuits 31 and 32 is “1”. When the output of the OR circuit 33 is “1”, the set value setting unit 34 increases the set value K1 of the ratio differential operation to K1 + KM (where KM> n · Ie). The control signal from the set value setting unit 34 is input to the ratio differential calculation unit 17 and the operation sensitivity of the ratio differential relay is changed. As a result, there is no output of the OR circuit 33 in the case of an internal failure, so there is no problem of reduced relay sensitivity due to the internal failure, and unnecessary operation due to electromagnetic induction of the current differential relay device is performed in a normal state or an external failure state. Can be prevented.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 1A, 1B current differential relay device, 2 input conversion block, 3 auxiliary transformer, 4,8 transformer, 5A, 5B, 5C, 6A, 6B, 6C, 7, 7A, 7B, 7C current transformer, DESCRIPTION OF SYMBOLS 11 Analog circuit, 12 Filter processing part, 13 Correction processing part, 14 1st difference current / suppression current calculation part, 15 2nd difference current / suppression current calculation part, 16 Settling value control part, 17 Ratio differential calculation part , 18 Failure determination unit, 19 output circuit, 20 open signal, 21 digital signal processing unit, 40 bus, 41 feeder line.

Claims (6)

A primary current flowing through the primary winding of the transformer, a secondary current flowing through the secondary winding of the transformer, and a neutral point of the primary or secondary winding or the primary and secondary windings; An AD converter for AD (Analog to Digital) conversion of each detected value of the neutral point current flowing through the neutral point provided in common;
A ratio differential calculation unit that performs ratio differential calculation based on the detected values of the AD converted primary current, secondary current, and neutral point current;
A settling value adjusting unit that adjusts a settling value that is a criterion for determining whether or not the transformer has an internal accident in the differential ratio calculation,
The settling value adjusting unit adjusts the settling value based on a comparison between the first determination value and the second determination value;
The first determination value is a zero-phase circuit calculated from a detected value of a current flowing through the winding having the neutral point of the primary current and the secondary current and a detected value of the neutral point current Is the magnitude of the difference current
The second determination value is obtained by inverting the sign of one of the detection value of the primary and secondary currents and the detection value of the neutral point current in the calculation of the first determination value. A current differential relay device, which is a value obtained by multiplying a detection value of a neutral point current by a predetermined constant.   2. The current according to claim 1, wherein the predetermined constant is set so as to cancel an error due to electromagnetic induction included in the detected values of the primary current, the secondary current, and the neutral point current. Differential relay device. The transformer is a three-phase transformer of Y-Δ connection or Δ-Y connection,
The first determination value is a magnitude of a value obtained by adding the current of the three-phase electric wire connected to the Y winding and the neutral point current,
3. The current differential relay device according to claim 1, wherein the second determination value is a magnitude of a value obtained by subtracting three times the neutral point current from the current of the three-phase electric wire. The transformer is an auto-transformer;
The first determination value is a magnitude of a value obtained by adding a primary current, a secondary current, and a neutral point current of the transformer,
3. The current differential according to claim 1, wherein the second determination value is a magnitude of a value obtained by subtracting twice the neutral point current from a sum of the primary current and the secondary current. Relay device. An AD converter for AD (Analog to Digital) conversion of detected values of currents of a plurality of lines connected to the bus;
A ratio differential calculation unit that performs ratio differential calculation based on the detected values of the respective currents of the plurality of lines subjected to AD conversion;
A settling value adjustment unit that adjusts a settling value that is a criterion for determining whether or not the bus has an internal accident in the ratio differential operation,
The settling value adjusting unit adjusts the settling value based on a comparison between the first determination value and the second determination value;
The first determination value is a magnitude of a difference current of a zero-phase circuit calculated from a detected value of each current of the plurality of lines.
In the calculation of the first determination value, the second determination value flows through a detection value of a current flowing through each odd-numbered arrangement line and among each even-numbered line in the calculation of the first determination value. A current differential relay device, which is a value obtained by inverting one sign of a detected current value. The settling value adjustment unit
A first condition that the first determination value is within a predetermined range, a second condition that the second determination value is smaller than a first reference value, and the first condition of the second determination value The third condition that the ratio to the determination value is larger than the second reference value, and the fourth condition that the value obtained by subtracting the first determination value from the second determination value is larger than the third reference value The success or failure of
When both the first and second conditions are satisfied, or when both the first, third and fourth conditions are satisfied, the set value is configured to be changed to a larger value. The current differential relay device according to any one of claims 1 to 5.

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