JP2013055735A - Transformer protection relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transformer protection relay that can avoid an unnecessary operation even if an oscillating resonant current generated after opening of a circuit breaker flows only to a CT at one end of a transformer.SOLUTION: The transformer protection relay includes: a ratio differential operation circuit 6; a second harmonic content detection circuit 9 for detecting a second harmonic component Ic in a differential current ID and determining whether or not a ratio of the second harmonic component Ic to an effective value Ib of a fundamental component in the differential current ID is at least a predetermined ratio; a harmonic content detection section 30 for determining whether or not a ratio of an effective value Id of harmonics to the effective value Ib of the fundamental component is at least a predetermined ratio (C); a shortage current operation circuit 14 for determining whether a predetermined value that is within a differential current ID operated after opening of a circuit breaker CB is not reached; and an on-delay circuit 18 for time-limiting an output from the ratio differential operation circuit 6 if the harmonic content detection section 30 determines that the predetermined ratio (C) is reached and the shortage current operation circuit 14 determines that the predetermined value (D) is not exceeded.

Description

  The present invention relates to a transformer protection relay that protects a transformer arranged in a power system by a current differential system, and more particularly to a current ratio differential element of a transformer protection relay.

  The transformer protective relay is a transformer high voltage transformer (CT) installed on a cable connected to a high voltage side and a low voltage side of a transformer arranged in a power system (hereinafter referred to as “system”). After taking in the side current and low side current, and correcting the current phase difference and amplitude ratio between the high voltage side and low voltage side caused by the transformer winding method and winding ratio, the difference composed of the vector sum of the currents at each terminal Ratio differential operation judgment is performed based on the current amount and the suppression current amount that is the scalar sum of each terminal current, and internal faults that occur inside the transformer (area surrounded by high-voltage side CT and low-voltage side CT) are detected. To do. When an internal failure is detected, the transformer protection relay includes a circuit breaker (CB1) disposed on the high voltage side of the transformer and a circuit breaker (CB2) disposed on the low voltage side of the transformer. The transformer is protected by opening and disconnecting the transformer from the grid.

  Here, when a transformer magnetizing inrush current occurs, a difference current is generated in the same manner as an internal failure even though an internal failure has not occurred. Therefore, an operation amount similar to that in an internal accident occurs. Therefore, the conventional transformer protection relay has a second harmonic content ratio (ratio of the second harmonic component to the fundamental wave component) in the differential current in order to distinguish between the magnetizing inrush current and the difference current due to internal failure. The operation based on the excitation inrush current is locked by using a method of discriminating from the excitation inrush current when the ratio is larger than the predetermined ratio. However, because the transient oscillation current component of the lower harmonics increases due to the increase of the charging capacity of the system, etc., the second harmonic content rate in the differential current due to internal failure increases, and in extreme cases, the difference current due to internal failure Includes a second harmonic equivalent to the second harmonic content of the magnetizing inrush current. Therefore, in the transformer protective relay, it is difficult to distinguish the magnetizing inrush current from the internal fault current due to the increased second harmonic content.

  As such a countermeasure, for example, Patent Document 1 below discloses a differential relay system that distinguishes between an inrush current and an internal fault current using an integrated value of a terminal voltage.

JP-A-6-54438 (paragraph 0004, paragraph 0005, etc.)

  However, in the prior art disclosed in Patent Document 1, as a method for discriminating between the magnetizing inrush current and the difference current at the time of an internal failure, a method in which identification by the second harmonic content rate and identification using the terminal voltage are combined. However, since there are actually many systems in which a voltage transformer for obtaining a terminal voltage is not installed, it may be impossible to distinguish between the magnetizing inrush current and the difference current at the time of internal failure. On the other hand, when a relatively long cable is connected to the high voltage side of the transformer and CB1 and CB2 disposed far from the cable are opened, the charge charged in the capacitance of the cable is transformed. In some cases, an oscillating resonance current (hereinafter referred to as “resonance current”) generated by repeating charging and discharging in resonance with the reactance of the coil windings flows. In this example, since this resonance current flows only to the high-voltage side CT, even though no internal fault current has occurred, a difference current is generated in the same way as an internal fault, resulting in the same amount of operation as an internal accident. Become. That is, the conventional technique represented by Patent Document 1 has a problem that unnecessary operation may occur due to a resonance current generated by the capacitance of the cable and the reactance of the transformer winding when the CB is opened.

  The present invention has been made in view of the above, and obtains a transformer protection relay capable of avoiding unnecessary operation even when a resonance current generated after the circuit breaker is opened flows only to CT at one end of the transformer. For the purpose.

  In order to solve the above-described problems and achieve the object, the present invention provides a high-voltage side current detected on a high-voltage side of a transformer provided in a power system and a low-voltage side current detected on a low-voltage side of the transformer. And a transformer protective relay comprising a ratio differential element that calculates a ratio differential operation based on the difference current and the suppression current. A ratio differential operation circuit for performing the ratio differential operation and outputting a result of the ratio differential operation; and detecting the second harmonic in the difference current and detecting the second harmonic with respect to the fundamental wave component in the difference current. A second harmonic content detection circuit that determines whether or not the ratio of the harmonic component is equal to or greater than a predetermined ratio, and locks the output of the ratio differential operation circuit according to the determination result; and a high frequency in the high-voltage side current To detect the fundamental wave component in the high-voltage side current. It is determined whether the ratio of the high frequency is equal to or higher than a predetermined ratio, and the high frequency in the low voltage side current is detected, and whether the ratio of the high frequency to the fundamental wave component in the low voltage side current is equal to or higher than the predetermined ratio Or a harmonic content detection unit that detects a high frequency in the difference current and determines whether a ratio of the high frequency with respect to a fundamental wave component in the difference current is equal to or higher than a predetermined ratio. A shortage current calculation circuit for determining whether an effective value of the difference current is less than a predetermined value that does not exceed a difference current calculated after opening a circuit breaker provided in the power system; and The time until the level of the difference current calculated after opening the device becomes equal to or less than the minimum operating sensitivity set in the ratio differential calculation circuit is set, and it is determined that the harmonic content detection unit is equal to or more than the predetermined ratio And the shortage An on-delay circuit that performs a time-limit operation on an output from the ratio differential arithmetic circuit when the time is determined to be equal to or less than a predetermined value by the flow arithmetic circuit. .

  According to the present invention, the harmonic content rate detection circuit is provided together with the second harmonic content rate detection circuit, and at the time of harmonic content detection, the time limit operation is performed in the operation region where the difference current amount is equal to or less than the predetermined set value. Therefore, even if the resonance current generated after the circuit breaker is opened flows only to the CT at one end of the transformer, an unnecessary operation can be avoided.

FIG. 1 is a diagram for explaining a generation mechanism of a resonance current. FIG. 2 is a configuration diagram of a ratio differential element of the transformer protection relay according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating an example of frequency characteristics of the harmonic extraction filter circuit illustrated in FIG. FIG. 4 is a configuration diagram of the ratio differential element according to the second exemplary embodiment of the present invention. FIG. 5 is a configuration diagram of a ratio differential element according to the third embodiment of the present invention. FIG. 6 is a configuration diagram of a ratio differential element according to the fourth embodiment of the present invention. FIG. 7 is a configuration diagram of a ratio differential element according to the fifth embodiment of the present invention.

  Hereinafter, an embodiment of a transformer protection relay according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a generation mechanism of a resonance current. FIG. 2 is a configuration diagram of the ratio differential element 100a of the transformer protection relay according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating an example of frequency characteristics of the harmonic extraction filter circuit 12 illustrated in FIG.

  FIG. 1 shows a transformer T arranged in the system, a cable C1 connected to the high voltage side of the transformer T, a cable C2 connected to the low voltage side of the transformer T, and a transformer arranged in the cable C1. CT1 which is an instrument transformer for detecting the high-voltage side current of the transformer T, CT2 which is an instrument transformer for detecting the low-voltage side current of the transformer T disposed on the cable C2, and detected by CT1 and CT2. Transformer protection relay (hereinafter referred to as “relay”) 100 that detects the internal fault that occurs in the transformer (area surrounded by CT1 and CT2) by taking in the amount of system electricity and is arranged in the cable C1. The provided circuit breaker CB1 and the circuit breaker CB2 disposed on the cable C2 are shown.

  Here, when a relatively long cable of, for example, 10 km is used as the cable C1 between the circuit breaker CB1 and the transformer T, when the circuit breaker CB1 and the circuit breaker CB2 are opened, this cable The charge charged in the capacitance C of C1 resonates with the reactance L of the winding of the transformer T, and charging and discharging are repeated. Therefore, there is a case where the resonance current flows only on the high-voltage side of the transformer T through a path (path where the capacitance C of the cable C1 and the reactance L of the winding of the transformer T are grounded) as indicated by an arrow. That is, the resonance current generated on the high voltage side of the transformer T flows into CT1 only because the circuit breaker CB2 on the low voltage side of the transformer T is open. A difference current is generated in the same manner as in FIG. And the transformer protection relay 100 operates unnecessary by this difference current. The relay 100 according to the present embodiment has a harmonic extraction filter circuit 12 for recognizing a resonance current in a ratio differential element 100a having a second harmonic lock function as means for avoiding such an unnecessary operation, and In addition to the undercurrent calculation circuit 14, an on-delay circuit 18 is added to prevent unnecessary operation (malfunction) associated with the resonance current.

  Hereinafter, the configuration of the differential ratio element 100a according to the first embodiment will be specifically described with reference to FIG. A ratio differential element 100a shown in FIG. 2 mainly includes a current input circuit 1, an amplitude phase correction circuit 2, a difference current calculation circuit 3, a suppression current calculation circuit 4, an effective value calculation circuit 5, and a fundamental wave component extraction filter. Circuit 7, second harmonic extraction filter circuit 8, harmonic content detection unit 30, overcurrent calculation circuit 11, ratio differential calculation circuit 6, second harmonic content detection circuit 9, undercurrent calculation circuit 14, with inhibit The circuit includes an AND circuit 10, an AND circuit 16 with an inhibit, an AND circuit 15, an AND circuit 17, an on-delay circuit 18, and an OR circuit 19. In addition, the harmonic content detection unit 30 includes a harmonic extraction filter circuit 12 and a harmonic content detection circuit 13.

  The high-voltage side current I1 detected by CT1 and the low-voltage side current I2 detected by CT2 are taken into the current input circuit 1. The high-voltage side current I1 and the low-voltage side current I2 taken into the current input circuit 1 are a filter circuit, a sampling circuit, and an AD (analog-to-digital conversion) circuit (both shown in the figure) that remove surge harmonics in the current input circuit 1. Is not converted into digital data.

  These digital data are taken into the amplitude / phase correction circuit 2. The amplitude phase correction circuit 2 corrects the phase difference due to the winding method of each CT1, CT2, transformer T, etc., and the amplitude value difference due to the winding ratio, and also matches these digital data as a differential relay input. The high-voltage side current data Ie1 and the low-voltage side current data Ie2 are output.

The high-voltage side current data Ie1 and the low-voltage side current data Ie2 are input to the difference current calculation circuit 3 and the suppression current calculation circuit 4, respectively. The difference current calculation circuit 3 executes instantaneous value data addition, and the suppression current calculation circuit 4 executes addition processing for the result of effective value calculation. That is,
Difference current ID = I1 + I2
Suppression current IR = | I1 | rms + | I2 | rms
(However, rms means that an effective value is calculated for the current in “||”.)

  The difference current ID from the difference current calculation circuit 3 is input to the effective value calculation circuit 5, the fundamental wave component extraction filter circuit 7, the second harmonic extraction filter circuit 8, and the harmonic extraction filter circuit 12, and the suppression current calculation circuit The suppression current IR from 4 is input to the ratio differential operation circuit 6.

  The effective value calculation circuit 5 performs an effective value calculation using the difference current ID, and outputs an effective value Ia that is the calculation result. The effective value Ia output from the effective value calculation circuit 5 is input to the overcurrent calculation circuit 11, the ratio differential calculation circuit 6, and the undercurrent calculation circuit 14.

  The output of the overcurrent calculation circuit 11 becomes “1” when the effective value Ia from the effective value calculation circuit 5 is equal to or greater than a predetermined set value (A), and is input to the OR circuit 19. This set value (A) is larger than the maximum value of the difference current ID accompanying the assumed transformer excitation inrush current, and is a value that can determine an internal failure.

  In the ratio differential operation circuit 6, the ratio differential operation is executed based on the suppression current IR and the effective value Ia, and the operation result is input to the inhibit AND circuit 10.

  The fundamental wave component extraction filter circuit 7 performs a filter operation on the difference current ID, extracts a fundamental wave (rated frequency) component, calculates an effective value, and calculates an effective value Ib of the fundamental wave component. The effective value Ib of the fundamental wave component extracted by the fundamental wave component extraction filter circuit 7 is input to the second harmonic content detection circuit 9 and the harmonic content detection circuit 13.

  The second harmonic extraction filter circuit 8 performs a filter operation on the difference current ID, extracts a second harmonic component, calculates an effective value, and calculates an effective value Ic of the second harmonic component. The effective value Ic of the second harmonic component is input to the second harmonic content detection circuit 9.

  The second harmonic content detection circuit 9 determines whether or not the ratio of the effective value Ic of the second harmonic component to the effective value Ib of the fundamental wave component is equal to or greater than a predetermined ratio (B), and determines a predetermined ratio ( B) When it is above, the output is “1”. This output is input to the inhibit AND circuit 10.

  The inhibit AND circuit 10 receives the inverted output from the second harmonic content detection circuit 9 and inputs the output from the ratio differential operation circuit 6. The output of the AND circuit 10 with the inhibit is “1” when the output of the second harmonic content detection circuit 9 is “0” and the output of the ratio differential operation circuit 6 is “1”. Input to the AND circuit 16 and the AND circuit 17.

  The harmonic extraction filter circuit 12 is a circuit that inputs the difference current ID, cuts and outputs the DC component and the fundamental wave component, and calculates the effective value after extracting the harmonics higher than the second harmonic. Then, the effective value Id of the harmonic is calculated. The harmonic effective value Id is input to the harmonic content detection circuit 13.

  The harmonic content detection circuit 13 determines whether or not the ratio of the harmonic effective value Id to the effective value Ib of the fundamental wave component is equal to or greater than a predetermined ratio (C). If the result is equal to or greater than the predetermined ratio (C), the output is “1” because the possibility of a resonance current is high. This output is input to the AND circuit 15.

  The undercurrent calculation circuit 14 determines whether or not the effective value Ia from the effective value calculation circuit 5 is less than a predetermined set value (D), and when it is less than the set value (D), the output is “1”. Become. This set value (D) is a current value that does not exceed the difference current ID that accompanies the resonance current that occurs after CB is opened. The output of the undercurrent calculation circuit 14 is input to the AND circuit 15.

  The AND circuit 15 takes the logical product of the output of the harmonic content detection circuit 13 and the output of the undercurrent calculation circuit 14, and the output of the AND circuit 15 is “1” as the output of the harmonic content detection circuit 13. Further, when the output of the undercurrent calculation circuit 14 is “1”, it becomes “1”, and is input to the AND circuit 16 with the inhibit and the AND circuit 17.

  The AND circuit 17 takes the logical product of the output of the AND circuit 10 with the inhibit and the output of the AND circuit 15, and the output of the AND circuit 17 is “1” as the output of the AND circuit 10 with the inhibit. When the output of 15 is “1”, it becomes “1” and is input to the on-delay circuit 18.

  In the on-delay circuit 18, the level of the resonance current that attenuates over time exceeds the time that is expected to be less than the minimum operating sensitivity of the ratio differential arithmetic circuit 6 (difference current level that is not detected by the ratio differential arithmetic). A predetermined time (T) is set. The on-delay circuit 18 outputs “1” after a predetermined time (T) has elapsed from the time when the output “1” from the AND circuit 17 is input. That is, when a predetermined time (T) has elapsed from the time when the output “1” from the AND circuit 17 is input, the level of the resonance current is less than the minimum operation sensitivity of the ratio differential operation circuit 6. .

  The inhibit AND circuit 16 inverts the input from the AND circuit 15 and inputs the output from the inhibit AND circuit 10. The output of the AND circuit 16 with the inhibit is “1” when the output of the AND circuit 15 is “0” and the output of the AND circuit 10 with the inhibit is “1”, and is input to the OR circuit 19.

  The OR circuit 19 receives the output from the overcurrent calculation circuit 11, the output from the AND circuit 16 with the inhibit, and the output from the on-delay circuit 18, and outputs the logical sum of these outputs as the current ratio differential element output. And

  Next, the operation will be described.

  As an internal failure countermeasure, the overcurrent calculation circuit 11 outputs “1” when the effective value Ia output from the effective value calculation circuit 5 is equal to or greater than a predetermined set value (A). That is, when the effective value Ia is larger than the magnetizing inrush current, it is considered that a fault current has flowed at the time of an internal fault. Therefore, the output “1” of the overcurrent calculation circuit 11 is OR-outputted by the OR circuit 19, and this output is the current ratio. Differential element output.

  The inhibit AND circuit 10 locks the output of the ratio differential arithmetic circuit 6 by the output of the second harmonic content detection circuit 9 as a countermeasure against malfunction due to the magnetizing inrush current of the transformer T. That is, when the output of the second harmonic content detection circuit 9 is “1”, the output “1” of the ratio differential operation circuit 6 is considered to be caused by the inrush current, and therefore the second harmonic content is included. When the output of the detection circuit 9 is “1”, the output of the AND circuit with inhibit 10 is “0”. Accordingly, the output of the AND circuit 16 with the inhibit is also “0” and is not ORed.

  Next, the operation of components for countermeasures against malfunction when a resonance current occurs will be described.

  First, when the ratio of the effective value Id of the harmonic to the effective value Ib of the fundamental component is equal to or greater than a predetermined ratio (C), the harmonic content detection circuit 13 detects the capacitance C of the cable C1 and the transformer winding when the CB is open. It is determined that there is a high possibility that a resonance current due to the reactance L of the line has occurred, and the output is set to “1”. Further, when the undercurrent calculation circuit 14 detects that the effective value Ia of the difference current ID is equal to or less than a predetermined set value (D), the output becomes “1”. The AND circuit 15 determines that the effective current Ia is equal to or less than a predetermined set value (B) in the undercurrent calculation circuit 14 and that there is a high possibility that a resonance current has occurred in the harmonic content detection circuit 13. If it is determined, it is determined that there is a high possibility that a resonance current is generated by the capacitance C of the cable C1 and the reactance L of the winding, and the output is set to “1”. Further, the AND circuit 17 determines that no exciting inrush current is generated in the inhibit AND circuit 10 and that the resonance current is generated in the AND circuit 15 due to the capacitance C of the cable C1 and the reactance L of the winding. If it is determined that the output is high, the output is set to “1”. The on-delay circuit 18 outputs when the output “1” of the ratio differential operation circuit 6 continues even after the elapse of a predetermined time (T) from the time when the output “1” from the AND circuit 17 is input. Becomes “1”. The time delay operation of the on-delay circuit 18 prevents an unnecessary operation (malfunction) associated with the resonance current, and enables a time limit operation for an internal failure that is equal to or less than a predetermined set value (D) of the undercurrent calculation circuit 14.

  Next, the frequency characteristics of the harmonic extraction filter circuit 12 will be supplemented. The frequency F of the resonance current is determined by F = 1 / (2π√ (L * C)), and is normally higher than the fundamental frequency, such as second-order and third-order harmonics. (Where C is the capacitance of the cable C1, and L is the reactance of the winding of the transformer T).

In order to extract such harmonic components, the harmonic extraction filter circuit 12 is used in the ratio differential element 100a according to the first embodiment. An example of an arithmetic expression of the harmonic extraction filter circuit 12 is as follows.
IDHF (t) = ID (t) -√3ID (t-30 °) + √3ID (t-90 °) −ID (t-120 °)
(However, IDHF (t) represents the output of the harmonic extraction filter circuit 12, and ID (t) represents the output of the difference current calculation circuit 3).

  With this arithmetic expression, the DC component and the fundamental wave component can be cut. FIG. 3 shows the frequency characteristics obtained by this calculation. The vertical axis represents the gain, and the horizontal axis represents the frequency (1f is the fundamental frequency). According to the above arithmetic expression, as shown in FIG. 3, the DC component (0f) and the fundamental wave component (1f) are completely cut, and a filter circuit capable of passing harmonics from 2f to 5f is realized. Can do. In the above description, a filter circuit that can pass harmonics from 2f to 5f has been described as an example. However, the filter circuit is not limited to this, and blocks DC component and 1f (fundamental wave) to prevent the 2f and later. Any material that can pass the higher harmonics is acceptable. After this filter calculation, an effective value calculation is executed.

  As described above, the ratio differential element 100a of the transformer protection relay 100 according to the first exemplary embodiment of the present invention extracts the harmonic component and removes the DC component and the fundamental component (harmonic extraction filter circuit). The harmonic content is calculated via 12). And when the content rate is larger than the predetermined ratio (C), it is determined that the possibility of the resonance current is high, and moreover than the current setting value (D) that cannot be exceeded at the difference current level caused by the resonance current. With respect to the ratio differential within the operation range of the low difference current ID, the on-delay circuit 18 is operated for a time limit to prevent malfunction due to the resonance current.

  On the other hand, with respect to an internal failure, when a difference current equal to or greater than the set value (A) is detected, the operation can be instantaneously performed. When a difference current less than the set value (D) is detected, the on-delay circuit 18 performs a time limit operation. Further, the differential differential arithmetic circuit 6 can operate for a difference current that is less than the set value (A) and greater than or equal to the set value (D). Since normal fault currents do not contain harmonics, timed operation can be avoided. That is, it is possible to suppress the possibility of a decrease in detection sensitivity against an internal failure. Even if the operation is limited due to the detection of harmonics, the fault current is small, so that the transformer T will not be seriously damaged.

  As described above, the transformer protection relay 100 according to the first embodiment is detected on the high voltage side current I1 detected on the high voltage side of the transformer T provided in the power system and on the low voltage side of the transformer T. The differential differential element 100a that calculates the differential current ID and the suppression current IR using the low-voltage side current I2 and performs the differential ratio calculation based on the differential current ID and the suppression current IR is provided. The differential ratio element 100a Includes a differential ratio calculation circuit 6 that performs a differential ratio calculation and outputs a result of the differential ratio calculation, and detects an effective value Ic of the second harmonic component in the difference current ID to detect the effective value Ic in the difference current ID. It is determined whether or not the ratio of the effective value Ic of the second harmonic component to the effective value Ib of the fundamental wave component is equal to or greater than a predetermined ratio (B), and the output of the ratio differential operation circuit 6 is locked based on the determination result. Second harmonic content detection circuit 9 and differential current ID A difference between the harmonic content detection unit 30 that detects the effective value Id of the high frequency and determines whether the ratio of the effective value Id of the high frequency to the effective value Ib of the fundamental component is equal to or greater than a predetermined ratio (C); The effective value Ia of the current ID is less than a predetermined value (set value (D)) that does not exceed the difference current ID (difference current ID associated with the resonance current) calculated after the circuit breaker CB provided in the power system is opened. And the time until the level of the difference current ID calculated after the circuit breaker CB is opened becomes less than the minimum operating sensitivity set in the ratio differential arithmetic circuit 6 (predetermined) Time (T)) is set, and it is determined by the harmonic content detector 30 that it is greater than or equal to a predetermined ratio (C), and it is determined by the undercurrent calculation circuit 14 that it is less than or equal to a predetermined value (D). When the specified time (T) is limited And an on-delay circuit 18 that performs a time-limited operation with respect to the output from the path 6, so that even if a resonance current generated after the circuit breaker is opened flows only to the CT at one end of the transformer, an unnecessary operation ( (Malfunction) can be avoided.

Embodiment 2. FIG.
The ratio differential element 100a according to the first embodiment recognizes the resonance current by detecting the harmonic effective value Id included in the difference current ID, and operates for a time limit with respect to the difference current ID equal to or less than a certain set value (D). By doing so, an unnecessary operation due to a resonance current generated when CB is released is prevented. The ratio differential element 100b according to the second embodiment uses the input current (the high-voltage side current I1 and the low-voltage side current I2) instead of the differential current ID, and the ratio of the harmonic components contained in this input current is the set value. It is configured to detect whether or not (C1 and C2). Hereinafter, the same parts as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Only different parts will be described here.

  FIG. 4 is a configuration diagram of the ratio differential element 100b according to the second exemplary embodiment of the present invention. The difference from the first embodiment is that a harmonic extraction filter circuit 12-1 and a harmonic extraction filter circuit 12-2 are used instead of the harmonic extraction filter circuit 12, and the harmonic content detection circuit 13 is replaced by a harmonic. The wave-containing detection circuit 13-1 and the harmonic-containing detection circuit 13-2 are used, and the fundamental wave component extraction filter circuit 7-1, the fundamental wave component extraction filter circuit 7-2, and the OR circuit 20 are used as new components. Is added. The harmonic content detection unit 31 includes a fundamental wave component extraction filter circuit 7-1, a fundamental wave component extraction filter circuit 7-2, a harmonic extraction filter circuit 12-1, a harmonic extraction filter circuit 12-2, and a harmonic content detection. The circuit 13-1, the harmonic content detection circuit 13-2, and the OR circuit 20 are included.

  Next, the operation will be described. The fundamental wave component extraction filter circuit 7-1 extracts the fundamental wave component from the high-voltage side current I1, and then calculates the effective value to calculate the effective value Ib1 of the fundamental wave component. The harmonic extraction filter circuit 12-1 After extracting the harmonics obtained by removing the DC component and the fundamental wave component from the current I1, the effective value is calculated, and the effective value Id1 of the harmonic is calculated. The effective value Ib1 of the fundamental wave component from the fundamental wave component extraction filter circuit 7-1 and the effective value Id1 of the harmonic wave from the harmonic extraction filter circuit 12-1 are input to the harmonic content detection circuit 13-1, and the harmonics are detected. The wave-containing detection circuit 13-1 sets the output to “1” when the ratio of the harmonic effective value Id1 to the effective value Ib1 of the fundamental wave component is equal to or greater than a predetermined ratio (C1).

  Similarly, in the low-voltage side current I2, the fundamental wave component extraction filter circuit 7-2 extracts the fundamental wave component from the low-voltage side current I2, and then calculates the effective value to calculate the effective value Ib2 of the fundamental wave component, thereby generating the harmonic. In the extraction filter circuit 12-2, the harmonic value obtained by removing the DC component and the fundamental wave component from the low-voltage side current I2 is extracted, and then the effective value calculation is performed to calculate the effective value Id2 of the harmonic. The effective value Ib2 of the fundamental wave component from the fundamental wave component extraction filter circuit 7-2 and the effective value Id2 of the harmonic wave from the harmonic extraction filter circuit 12-2 are input to the harmonic content detection circuit 13-2. The wave-containing detection circuit 13-2 sets the output to “1” when the ratio of the harmonic effective value Id2 to the effective value Ib2 of the fundamental wave component is equal to or greater than a predetermined ratio (C2).

  The outputs of the harmonic content detection circuit 13-1 and the harmonic content detection circuit 13-2 are input to an OR circuit 20 that takes a logical sum, and input to the AND circuit 15 as an output of the OR circuit 20. In other words, the outputs of the harmonic content detection circuit 13-1 and the harmonic content detection circuit 13-2 are output when harmonics are detected at a set value or higher in either the high-voltage side current I1 or the low-voltage side current I2.

  The AND circuit 15 takes a logical product of the output of the OR circuit 20 and the output of the undercurrent calculation circuit 14. The output of the AND circuit 15 is “1” when the output of the OR circuit 20 is “1” and the output of the undercurrent calculation circuit 14 is “1”, and is input to the AND circuit 16 with the inhibit and the AND circuit 17. Is done.

  In this way, the output of the OR circuit 20 and the output of the undercurrent calculation circuit 14 are ANDed by the AND circuit 15, and a harmonic is detected in excess of the set value for either the high-voltage side current I1 or the low-voltage side current I2. In some cases, the malfunction due to the resonance current is prevented by performing the time-limited operation on the ratio differential within the operation range of the difference current ID equal to or less than the predetermined set value (D). For internal failure, as in the first embodiment, when a difference current greater than or equal to the set value (A) is detected, the internal failure is caused to occur, and the set value (D) less than the set value (A). The above differential current can be operated by the ratio differential arithmetic circuit 6, and the differential current less than the set value (D) can be operated for a limited time by the on-delay circuit 18 even if a harmonic is detected.

  As described above, in the ratio differential element 100b according to the second embodiment, the harmonic content detection unit 31 detects the high-frequency effective value Id1 in the high-voltage side current I1 and The harmonic content detection circuit 13-1 for determining whether or not the ratio of the effective value Id1 of the high frequency to the effective value Ib1 of the fundamental component is equal to or higher than a predetermined ratio (C1), and the high frequency in the low voltage side current I2 Harmonic content detection that detects the effective value Id2 and determines whether the ratio of the effective value Id2 of the high frequency to the effective value Ib2 of the fundamental wave component in the low-voltage side current I2 is equal to or higher than a predetermined ratio (C2). The on-delay circuit 18 is output from the harmonic content detection circuit 13-1 or the harmonic content detection circuit 13-2, and the undercurrent calculation circuit 14 outputs a predetermined value (D). Determined to be Since the time limit operation is performed on the output from the ratio differential arithmetic circuit 6 with the predetermined time (T) as the time limit, the reliability of the protection operation can be improved as in the first embodiment. Is possible.

Embodiment 3 FIG.
The ratio differential element 100b of the second embodiment recognizes the resonance current by detecting the harmonics included in the high-voltage side current I1 and the low-voltage side current I2, and with respect to the difference current ID that is equal to or less than a certain set value (D) Thus, it is configured to prevent an unnecessary operation due to a resonance current generated when the CB is opened by performing the time-limited operation. The ratio differential element 100c according to the third embodiment detects the resonance current as a condition for detecting the high-frequency side harmonic when detecting the high-voltage side harmonic, and detecting the low-frequency side harmonic. In this case, by adding a condition that the high-voltage side current I1 is absent, the possibility of erroneously recognizing the resonance current (possibility of time-limited operation) is reduced. Hereinafter, the same reference numerals are given to the same parts as those of the second embodiment, and the description thereof is omitted, and only different parts will be described here.

  FIG. 5 is a configuration diagram of the ratio differential element 100c according to the third embodiment of the present invention. The difference from the second embodiment is that an undercurrent calculation circuit 21-1, an undercurrent calculation circuit 21-2, an AND circuit 22-1, and an AND circuit 22-2 are added as new components. It is. The harmonic content detection unit 32 includes a fundamental wave component extraction filter circuit 7-1, a fundamental wave component extraction filter circuit 7-2, a harmonic extraction filter circuit 12-1, a harmonic extraction filter circuit 12-2, and a harmonic content detection. A circuit 13-1, a harmonic content detection circuit 13-2, an undercurrent calculation circuit 21-1, an undercurrent calculation circuit 21-2, an AND circuit 22-1, an AND circuit 22-2, and an OR circuit 20; It is configured.

  When an internal failure occurs, the harmonic component contained in the current detected at each terminal is small, so the time delay operation of the on-delay circuit 18 is unlikely to be performed, but the time limit operation can be performed by this high frequency component. There is also sex. The undercurrent calculation circuit 21-1 and the undercurrent calculation circuit 21-2 are terminals that do not detect harmonics (for example, CT2 shown in FIG. 1) in order to reduce the possibility that the time-limited operation is performed when an internal failure occurs. A condition for detecting no current is given to the detected current.

  Next, the operation will be described. The undercurrent calculation circuit 21-1 is used for detecting no current of the low-voltage side current I2. When the low-voltage side current I2 is less than a predetermined set value (E), the output becomes “1”. The output of the undercurrent calculation circuit 21-1 is input to the AND circuit 22-1.

  The undercurrent calculation circuit 21-2 is used for detecting no current of the high-voltage side current I1, and the output becomes “1” when the high-voltage side current I1 is less than a predetermined set value (E). The output of the undercurrent calculation circuit 21-2 is input to the AND circuit 22-2.

  The AND circuit 22-1 determines that the ratio of the harmonic effective value Id1 to the effective value Ib1 of the fundamental wave component in the harmonic content detection circuit 13-1 is equal to or greater than a predetermined ratio (C1), and an undercurrent calculation circuit. If it is determined in 21-1 that the low-voltage side current I2 is not detected, the high-voltage side harmonic is detected and “1” indicating that the low-voltage side current I2 is not detected is output.

  The output of the AND circuit 22-2 is determined by the harmonic content detection circuit 13-2 that the ratio of the effective value Id2 of the harmonic to the effective value Ib2 of the fundamental component is equal to or greater than a predetermined ratio (C2), and the shortage current When the arithmetic circuit 21-2 determines that the high-voltage side current I1 is not detected, the low-frequency side harmonic is detected and “1” indicating that the high-voltage side current I1 is not detected is output.

  Each output of the AND circuit 22-1 and the AND circuit 22-2 is input to an OR circuit 20 that takes a logical sum, and any output is input to the AND circuit 15.

  The AND circuit 15 takes the logical product of the output of the OR circuit 20 and the output of the undercurrent operation circuit 14, and the output of the AND circuit 15 is that the output of the OR circuit 20 is "1" and the undercurrent operation circuit When the output of 14 is “1”, it becomes “1” and is input to the AND circuit 16 with the inhibit and the AND circuit 17.

  In this way, by ANDing the output of the OR circuit 20 and the output of the undercurrent calculation circuit 14 with the AND circuit 15, a predetermined set value (with respect to any harmonic of the high-voltage side current I1 and the low-voltage side current I2) D) The time-limited operation is performed on the differential ratio within the operation range of the following difference current ID, and malfunction due to the resonance current is prevented. For internal failure, as in the first embodiment, when a difference current greater than or equal to the set value (A) is detected, the internal failure is caused to occur, and the set value (D) less than the set value (A). The above differential current can be operated by the ratio differential arithmetic circuit 6, and the differential current less than the set value (D) can be operated for a limited time by the on-delay circuit 18 even if a harmonic is detected.

  In addition, the differential ratio element 100c according to the third embodiment is configured to recognize the resonance current as a condition for detecting a high-frequency harmonic, and that there is no low-voltage current I2 when detecting a high-voltage harmonic. In the case of detecting a wave, a condition that there is no high-voltage side current I1 is added. By adding such no current detection to the condition, it is possible to prevent unnecessary operation by becoming a time-limited operation for the resonance current, and even when the harmonic component is small when an internal failure occurs, It is possible to reduce the possibility that the time-limited operation is executed depending on the no-current detection condition.

  As described above, in the ratio differential element 100c according to the third embodiment, the harmonic content detection unit 32 detects the high frequency in the high-voltage side current I1, and the fundamental wave component in the high-voltage side current I1 is detected. A first harmonic content detection circuit (13-1) for determining whether or not the ratio of the effective value Id1 of the high frequency to the effective value Ib1 is equal to or higher than a predetermined ratio (C1), and the low-voltage side current I2 is a predetermined value A first undercurrent calculation circuit (21-1) for determining whether or not the value is less than the set value (E) and a high frequency in the low voltage side current I2 are detected, and a fundamental wave component in the low voltage side current I2 is detected. A second harmonic content detection circuit (13-2) for determining whether or not the ratio of the effective value Id2 of the high frequency to the effective value Ib2 is equal to or greater than a predetermined ratio (C2), and the high-voltage side current I1 is a predetermined value Second deficiency to determine whether it is less than the set value (E) The on-delay circuit 18 has a ratio of the effective value Id1 of the harmonic to the effective value Ib1 of the fundamental component in the first harmonic content detection circuit (13-1). It is determined that the ratio is equal to or greater than a predetermined ratio (C1), and the first undercurrent calculation circuit (21-1) determines that the low-voltage side current I2 is not detected, or the second harmonic content detection circuit (13-2) ), The ratio of the effective value Id2 of the harmonic to the effective value Ib2 of the fundamental wave component is determined to be equal to or greater than a predetermined ratio (C2), and the high-voltage side current I1 is absent in the second undercurrent calculation circuit (21-2). When it is determined to be detected and the undercurrent calculation circuit 14 determines that the value is equal to or less than the predetermined value, the time limit operation is performed on the output from the ratio differential calculation circuit 6 with the time being limited. More reliable protection operation than Embodiments 1 and 2 It is possible to improve.

Embodiment 4 FIG.
In the differential differential element 100c of the third embodiment, the condition for recognizing the resonance current is that there is no low-voltage side current I2 in the case of high-frequency harmonic detection, and high-voltage current I1 in the case of low-voltage harmonic detection. In addition, it is configured to reduce the possibility of being misidentified as a resonance current when an internal failure occurs. The ratio differential element 100d of the fourth embodiment is configured such that harmonic detection and no current detection can be manually set according to system conditions in order to simplify the circuit. Hereinafter, the same reference numerals are given to the same parts as those of the third embodiment, and the description thereof is omitted, and only different parts will be described here.

  FIG. 6 is a configuration diagram of a ratio differential element 100d according to the fourth exemplary embodiment of the present invention. The difference from the third embodiment is that a first selection circuit 23-1 and a second selection circuit 23-2 are added as new components, and a fundamental wave component extraction filter circuit 7- 2, the harmonic extraction filter circuit 12-1, the undercurrent calculation circuit 21-2, the harmonic content detection circuit 13-2, and the AND circuit 22-2 are excluded. The harmonic content detection unit 33 includes a fundamental wave component extraction filter circuit 7-1, a harmonic extraction filter circuit 12-1, a harmonic content detection circuit 13-1, an AND circuit 22-1, an undercurrent calculation circuit 21-1, The first selection circuit 23-1 and the first selection circuit 23-1 are included.

  Next, the operation will be described. The first selection circuit 23-1 and the second selection circuit 23-2 are circuits that select the low-voltage side current I2 or the high-voltage side current I1. However, the second selection circuit 23-2 selects a current opposite to the current selected by the first selection circuit 23-1. That is, when the high voltage side current I1 is selected by the first selection circuit 23-1, the low voltage side current I2 is selected by the second selection circuit 23-2.

  Here, when the circuit breaker CB1 and the circuit breaker CB2 are opened, as shown in FIG. 1, since the circuit breaker CB2 on the low voltage side is opened, a resonance current flows only in the cable C1 on the high voltage side. ID. In this way, when the resonance current flows only to one of the transformers T, the first selection circuit 23-1 and the second selection circuit 23-2 make the harmonic detection side and the current non-detection. It is possible to set the side. For example, by selecting the high-voltage side current I1 in the first selection circuit 23-1, and selecting the low-voltage side current I2 in the second selection circuit 23-2, the harmonics of the high-voltage side current I1 are detected, and The low-voltage side current I2 non-detection condition is satisfied.

  With this configuration, for example, with respect to the harmonics of the high-voltage side current I1, a time-limited operation is performed on the ratio differential within the operation range of the difference current ID equal to or less than a predetermined setting value (D), and resonance Malfunction due to current is prevented. For internal failure, as in the first embodiment, when a difference current greater than or equal to the set value (A) is detected, the internal failure is caused to occur, and the set value (D) less than the set value (A). The above differential current can be operated by the ratio differential arithmetic circuit 6, and the differential current less than the set value (D) can be operated for a limited time by the on-delay circuit 18 even if a harmonic is detected.

  Furthermore, according to the differential ratio element 100d according to the fourth embodiment, as in the third embodiment, the resonance current can be operated for a limited time to prevent unnecessary operation, and when an internal failure occurs. Even when there are few harmonic components, it is possible to reduce the possibility that the time-limited operation is executed due to the no-current detection condition.

  As described above, the ratio differential element 100d according to the fourth exemplary embodiment includes the first selection circuit 23-1, in which the harmonic content detection unit 33 selects the low-voltage side current I2 or the high-voltage side current I1, A second selection circuit 23-2 in which a current (for example, a low-voltage side current I2) opposite to the current (for example, the high-voltage side current I1) selected by the first selection circuit 23-1 is selected; The high frequency in the current selected by the circuit 23-1 is detected, and the ratio of the effective value Id of the high frequency to the effective value Ib of the fundamental wave component in the selected current is a predetermined ratio (in the selection circuit 23-1. Harmonic content detection circuit 13-1 for determining whether or not C1 when the high-voltage side current I1 is selected, or C2) when the low-voltage side current I2 is selected, and a second selection circuit If the current selected in 23-2 is less than the preset value (E) And the on-delay circuit 18 is a harmonic with respect to the effective value Ib of the fundamental wave component in the harmonic content detection circuit 13-1. It is determined that the ratio of the component Id is equal to or greater than a predetermined ratio (C1 or C2), it is determined that no current is detected by the undercurrent calculation unit (the undercurrent calculation circuit 21-1), and the predetermined value is determined by the undercurrent calculation circuit 14. Since the time limit operation is performed on the output from the ratio differential arithmetic circuit 6 when the time is determined as the time limit, the reliability of the protection operation is more reliable than the first and second embodiments. It is possible to improve. Further, the circuit can be simplified as compared with the third embodiment.

Embodiment 5 FIG.
In the first to fourth embodiments, the harmonic content detection circuit 13 or the like is used as a condition for recognizing the resonance current, but in the fifth embodiment, a signal related to the CB release command is used instead of the harmonic content detection circuit 13 or the like. A signal input circuit 24 is provided. By using a CB release signal from the signal input circuit 24, a time limit operation is performed on a difference current ID that is equal to or less than a predetermined set value (D). Unnecessary operation is prevented, and the circuit is further simplified. Hereinafter, the same reference numerals are given to the same parts as those in the first to fourth embodiments, and the description thereof will be omitted, and only different parts will be described here.

  FIG. 7 is a configuration diagram of a ratio differential element 100e according to the fifth embodiment of the present invention. For example, the difference from the first embodiment is that a signal input circuit 24 is used instead of the harmonic extraction filter circuit 12 and the harmonic content detection circuit 13. The signal input circuit 24 is a circuit for inputting a CB release signal, which is a DC signal, and this CB release signal is a command for opening, for example, CB1 and CB2 shown in FIG. When this CB opening signal is output, a resonance current generated after opening CB1 and CB2 flows. The fifth embodiment is configured to predict the generation of a resonance current and prevent malfunction by taking in this CB release signal.

  Next, the operation will be described. When the CB release signal is input, the time-limited operation for the ratio differential within the operation range of the difference current ID equal to or less than the predetermined setting value (D) becomes effective, and thus malfunction due to the resonance current is prevented. Also, for internal faults, as in the first to fourth embodiments, when a fault current greater than the set value (A) is detected, it can be operated instantaneously.

  As described above, the ratio differential element 100e according to the fifth embodiment includes the signal input circuit 24 that takes in the CB open signal from the outside of the transformer protection relay 100 in place of the harmonic content detection units 30 to 33. The on-delay circuit 18 receives the CB release signal from the signal input circuit 24 and determines that the short-circuit current calculation circuit 14 determines that the signal is less than or equal to a predetermined value. Since the time-limited operation is performed on the output of, as in the first to fourth embodiments, the reliability of the protection operation can be improved and the harmonic content detection units 30 to 33 can be omitted. It is possible to simplify the circuit.

  Thus, the ratio differential elements 100a to 100e according to the first to fifth embodiments detect the high frequency in the ratio differential arithmetic circuit 6, the second harmonic content detection circuit 9, and the high-voltage side current I1. It is determined whether or not the ratio of the effective value Id1 of the high frequency to the effective value Ib1 of the fundamental wave component in the high voltage side current I1 is equal to or higher than a predetermined ratio (C1), and the high frequency in the low voltage side current I2 is detected. It is determined whether the ratio of the effective value Id2 of the high frequency to the effective value Ib2 of the fundamental wave component in the low-voltage side current I2 is equal to or greater than a predetermined ratio (C2), or the high frequency in the difference current ID is determined. Harmonic content detection units 30 to 33 that detect and determine whether the ratio of the effective value Id of the high frequency to the effective value Ib of the fundamental wave component in the difference current ID is equal to or greater than a predetermined ratio (C); , Undercurrent calculation circuit 14 and Since such includes a delay circuit 18, a resonance current generated after opening of the circuit breaker can be avoided even unnecessary operation flow only CT end of the transformer.

  In the above description, the case of the transformer protection relay 100 has been described as an example of the application of the present invention. However, the present invention is also used in the case where a difference current occurs due to the resonance phenomenon of the cable capacitance C and the external reactance in other power transmission lines. it can.

  Moreover, the transformer protection relay shown in Embodiments 1 to 5 shows an example of the content of the present invention, and can be combined with another known technique. Of course, it is possible to change and configure such as omitting a part without departing from the scope.

  As described above, the present invention can be applied to a transformer protective relay, and in particular, unnecessary operation can be avoided even if a resonance current generated after the circuit breaker is opened flows only to the CT at one end of the transformer. It is useful as an invention.

DESCRIPTION OF SYMBOLS 1 Current input circuit 2 Amplitude phase correction circuit 3 Difference current calculation circuit 4 Inhibition current calculation circuit 5 Effective value calculation circuit 6 Ratio differential calculation circuit 7, 7-1, 7-2 Fundamental wave component extraction filter circuit 8 Second harmonic Extraction filter circuit 9 Second harmonic content detection circuit 10, 16 AND circuit with inhibit 11 Overcurrent operation circuit 12, 12-1, 12-2 Harmonic extraction filter circuit 13, 13-1, 13-2 Harmonic content detection Circuit 14 Undercurrent calculation circuit 15, 17, 22-1, 22-2 AND circuit 18 On-delay circuit 19, 20 OR circuit 21-1, 21-2 Undercurrent calculation circuit 23-1 First selection circuit 23-2 Second selection circuit 24 Signal input circuit 30, 31, 32, 33 Harmonic content detection unit 100 Transformer protection relay 100a, 100b, 100c, 100d, 100e Ratio Differential element C Capacitance C1, C2 Cable CB1, CB2 Circuit breaker CT1, CT2 Instrument transformer I1 High voltage side current I2 Low voltage side current ID Difference current IR Suppression current Ia RMS value Ib, Ib1, Ib2 RMS value of fundamental wave component Ic Effective value of second harmonic component Id, Id1, Id2 Effective value of harmonic Ie1 High-voltage side current data Ie2 Low-voltage side current data L Reactance T Transformer

Claims (5)

Using the high-voltage side current detected on the high-voltage side of the transformer provided in the power system and the low-voltage side current detected on the low-voltage side of the transformer to calculate the difference current and the suppression current, the difference current and the A transformer protection relay having a ratio differential element that performs ratio differential operation based on a suppression current,
The ratio differential element is:
A ratio differential operation circuit that performs the ratio differential operation and outputs a result of the ratio differential operation;
The second harmonic component in the difference current is detected to determine whether the ratio of the second harmonic component to the fundamental wave component in the difference current is equal to or greater than a predetermined ratio, and the determination result determines the A second harmonic content detection circuit that locks the output of the ratio differential operation circuit;
The high frequency in the high voltage side current is detected to determine whether the ratio of the high frequency to the fundamental wave component in the high voltage side current is equal to or higher than a predetermined ratio, and the high frequency in the low voltage side current is detected. It is determined whether the ratio of the high frequency to the fundamental wave component in the low-voltage side current is equal to or higher than a predetermined ratio, or the high frequency in the difference current is detected to detect the high frequency component in the difference current. A harmonic content detection unit that determines whether or not the ratio of the high frequency is equal to or higher than a predetermined ratio;
An insufficient current calculation circuit for determining whether the effective value of the difference current is less than a predetermined value that does not exceed the difference current calculated after the circuit breaker provided in the power system is opened;
The time until the level of the difference current calculated after the circuit breaker is opened is less than the minimum operating sensitivity set in the ratio differential calculation circuit is set, and the harmonic content detection unit is greater than or equal to the predetermined ratio And an on-delay circuit that performs a time limit operation on the output from the ratio differential operation circuit with the time as a time limit when it is determined that the undercurrent calculation circuit is equal to or less than a predetermined value,
A transformer protective relay characterized by comprising: The harmonic content detector is
A harmonic content detection circuit that detects a high frequency in the high-voltage side current and determines whether the ratio of the high frequency to the fundamental wave component in the high-voltage side current is equal to or higher than a predetermined ratio;
A harmonic content detection circuit that detects a high frequency in the low-voltage side current and determines whether or not a ratio of the high frequency to a fundamental wave component in the low-voltage side current is equal to or higher than a predetermined ratio;
With
The on-delay circuit is
When it is determined that the harmonic content detection circuit or the harmonic content detection circuit is equal to or greater than the predetermined ratio, and the undercurrent calculation circuit determines that it is equal to or less than a predetermined value, the time is limited to the time limit. 2. The transformer protection relay according to claim 1, wherein a time-limited operation is performed on the output from the ratio differential arithmetic circuit. The harmonic content detector is
A first harmonic content detection circuit that detects a high frequency in the high-voltage side current and determines whether or not a ratio of the high-frequency wave to a fundamental wave component in the high-voltage side current is equal to or higher than a predetermined rate;
A first undercurrent calculation circuit for determining whether or not the low-voltage side current is less than a predetermined set value;
A second harmonic content detection circuit that detects a high frequency in the low-voltage side current and determines whether or not a ratio of the high-frequency wave to a fundamental wave component in the low-voltage side current is equal to or higher than a predetermined rate;
A second undercurrent calculation circuit for determining whether or not the high-voltage side current is less than a predetermined set value;
With
The on-delay circuit is
The first harmonic content detection circuit determines that the ratio of the harmonic component to the fundamental component is equal to or greater than a predetermined ratio, and the first insufficient current calculation circuit determines that the low-voltage side current is not detected, or The second harmonic content detection circuit determines that the ratio of the harmonic component to the fundamental wave component is equal to or greater than a predetermined ratio, and the second insufficient current calculation circuit 2 determines that the high-voltage side current is not detected, and The time limit operation is performed on the output from the ratio differential operation circuit when the time is determined to be a predetermined value or less by the undercurrent calculation circuit. Transformer protection relay. The harmonic content detector is
A first selection circuit for selecting the low-voltage side current or the high-voltage side current;
A second selection circuit in which a current opposite to the current selected by the first selection circuit is selected;
Harmonic inclusion detection for detecting a high frequency in the current selected by the first selection circuit and determining whether a ratio of the high frequency to a fundamental wave component in the selected current is equal to or higher than a predetermined ratio. Circuit,
An undercurrent calculator that determines whether or not the current selected by the second selection circuit is less than a predetermined set value;
With
The on-delay circuit is
The harmonic content detection circuit determines that the ratio of the harmonic component to the fundamental wave component is equal to or higher than a predetermined ratio, the undercurrent calculation unit determines that no current is detected, and the undercurrent calculation circuit determines a predetermined value. 2. The transformer protection relay according to claim 1, wherein when it is determined that the value is equal to or less than a value, the time is limited to perform a time limit operation on an output from the ratio differential operation circuit. The ratio differential element is provided with a signal input circuit that takes in an open signal of the circuit breaker from the outside of the transformer protection relay, instead of the harmonic content detection unit,
The on-delay circuit receives the open signal at the signal input circuit and determines that the undercurrent calculation circuit determines that the open current signal is equal to or less than a predetermined value from the ratio differential calculation circuit with a time limit. The transformer protection relay according to claim 1, wherein a time-limited operation is performed on the output of the transformer.

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