JP2000152490A - Differential relay for protection of parallel transformer bank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the malfunction of a differential relay caused by an excited rush current which is generated in case that another transformer is energized in addition to one transformer. SOLUTION: This differential relay (1-3.9) detects the difference between the primary and secondary currents (ip) and (is) of a transformer 1 and compares the effective value of the current value (id) with a set value ids, and outputs a trip signal when the current difference id is large. In this case, this is provided with a malfunction preventive circuit comprising an integration circuit 4 which gets the magnetic flux ϕ of a transformer by integrating the primary voltage of the transformer, a comparison circuit which compares this magnetic flux ϕ with a set value ϕs and outputs a signal at the time of ϕ>ϕs, and a logical circuit 81 which checks the output of a trip signal in case that there is output of the comparison circuit 7. Since the magnetic flux ϕof the transformer is small at the timer of internal accident and is large at the time of excitation rush, it can prevent the malfunction of the differential relay at the time of excitation rush.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for preventing malfunction of a differential relay used as a protection device for a parallel transformer bank.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential operation relay for protecting a parallel transformer bank provided with a malfunction prevention circuit.

FIGS. 5 to 7 show examples of operation of a power transformer (1).
(3) is shown. 5 is a transformer TR that operates in parallel.
The common input and output currents of A and TRB are converted to current transformers CT1 and CT.
2, the internal fault of the transformers operated in parallel by the ratio-actuated relay T is detected, and the common circuit breakers CB1 and CB2 are tripped to disconnect and protect the transformers TRA and TRB.

FIG. 6 shows a transformer TRA, which operates in parallel.
The input and output currents of TRB are detected by current transformer CT, respectively.
Internal faults in the transformers TRA and TRB are individually detected by the ratio differential relays A and B, and the common circuit breakers CB1 and CB2 are tripped to disconnect and protect the transformers TRA and TRB.

FIG. 7 shows transformers TRA and TRB operating in parallel.
The respective input and output currents are detected by the current transformer CT, the internal faults of the transformers TRA and TRB are detected by the ratio difference relays A and B, respectively, and the circuit breaker of the internal fault transformer TRA or TRB is tripped. Transformer TRA or T with internal failure
Disconnect and protect the RB.

FIG. 8 shows a block diagram of a conventional ratio differential relay. In the figure, 1 is a current difference detection circuit for detecting a difference between a primary current ip and a secondary current is of a transformer, 2 is an effective value calculation circuit for obtaining an effective value of the current difference id, and 3 is this current effective value. And a set value, and outputs a signal when the effective current value is large. Reference numeral 9 denotes a timed circuit for checking the output of the comparator and outputting a trip signal of the circuit breaker.

[0007] As a method of protecting an isolated transformer,
The magnetic flux density at the time when the current difference between the terminals of the transformer exceeds the set value, or when the current difference exceeds the set value once and returns to the set value again, is set to a predetermined value set in advance. On the other hand, there is a method in which, based on the instantaneous value of the current, when the difference from the magnetization curve of the transformer is equal to or less than the set value, it is determined to be normal, and when the difference is equal to or more than the set value, it is determined that an internal failure has occurred. (JP-A-9-46890)

[0008]

In the conventional method shown in FIG. 5, when one of the transformers TRA or TRB fails, the detection currents of the current transformers CT1 and CT2 that operate the ratio differential relay T include: Since the current of the sound transformer is included, it is not preferable in protection relay technology. Further, even if one transformer fails, both transformers are disconnected.

In the conventional system shown in FIG. 6, the ratio differential relays A and B are operated by the input and output currents of the transformers TRA and TRB, respectively, but the circuit breaker CB is shared. Therefore, as in the case of FIG. 5, even if one of the transformers fails, two of the transformers are disconnected.

In the conventional system shown in FIG. 7, when one transformer TRB is already energized and another transformer TRA is energized as shown in FIG. 9, the system is already energized. Exciting inrush current also flows through the transformer, which may cause the ratio differential relay B to malfunction. (Susumu Kobayashi: Protective Relay Technology (Showa 47) Denki Shoin p254-p255.) The present invention has been made in view of the above-mentioned problem, and a purpose thereof is to make one transformer already energized. The present invention is to provide a differential transformer for protecting a parallel transformer bank which prevents a differential relay from malfunctioning due to an inrush current generated when another transformer is energized in a place where the transformer is operated. .

[0011]

According to the present invention, there is provided a differential relay for protecting a parallel transformer bank provided in each transformer, an integrating circuit for integrating a voltage at a primary terminal of the transformer to obtain a magnetic flux of the transformer. And a circuit for preventing the output of the trip signal of the differential relay when the absolute value of the magnetic flux is compared with the set value and the absolute value is large.

In a differential relay for protecting a parallel transformer bank provided in each transformer, an integrating circuit for integrating a primary terminal voltage of the transformer to obtain a magnetic flux of the transformer; And a circuit for detecting that the gradient of the magnetic flux-primary and secondary current difference characteristics is smaller than a set value and preventing the output of the trip signal of the differential relay. It is.

Then, from the magnetic flux, the magnetic flux of the transformer-1
Next, a circuit that detects that the slope of the secondary current difference characteristic is smaller than a set value and blocks the output of the trip signal of the differential relay includes a circuit that delays the magnetic flux from the integration circuit for a minute time, A comparison circuit that compares the difference between the current value and the delayed magnetic flux with the set value and outputs a signal when the difference between the magnetic flux is greater than the set value, and outputs a trip signal of the differential relay on condition that there is an output of the comparison circuit. And a logical product circuit for performing the operation.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram of a transformer using this ratio differential relay, and FIG. 2 shows a parallel operation circuit of the transformer using this ratio differential relay.

The ratio differential relay of FIG. 1 is the same as the conventional ratio differential relay (1 to 3, 9) shown in FIG. 8 except that a malfunction prevention circuit (4, 7, 8) is provided. As shown, the protection ratios of the transformers TRA, TRB are used as differential relays A, B.

The ratio differential relay operation units (1 to 3) of the ratio differential relays A and B have the same configuration as that of the conventional one shown in FIG. 7, and the primary and secondary currents of the transformers TRA and TRB. ip, is
, The current difference id between the currents ip and is detected by the current difference detection circuit 1, the effective value of the current difference id is obtained by the effective value calculation circuit 2, and the effective value and the set value of the current difference id are obtained by the comparison circuit 3. is compared with ids, and when the effective value of id> ids, a trip signal is output.

The malfunction prevention circuits (4, 7, 8) of the ratio differential relays A and B are connected to one of the transformers TRA and TRB, respectively.
An integrating circuit 4 that integrates the secondary voltage vp and outputs a magnetic flux φ of the transformer, and sets an absolute value | φ |
A comparator 7 that outputs when | φ |> φs, and a logic circuit 8 that outputs a trip signal from the comparison circuit 3 to the time limit circuit 9 on condition that there is no input from the comparison circuit 7 _{Consists of one} .

This ratio differential relay has the malfunction prevention circuit as described above, and integrates the primary voltage of the transformer to obtain the magnetic flux φ.
And the value of the magnetic flux is used as a criterion for determining whether or not the current is the inrush current of the transformer. The magnetic flux φ is small at the time of an accident inside the transformer and large at the time of inrush.

Therefore, for example, one transformer T in FIG.
When the other transformer TRA is energized where RB is energized, an inrush current flows through the already energized transformer TRB, and the ratio differential operation unit (1) of the ratio differential relay B
3) cause a malfunction and output a trip signal from the comparator 3. The malfunction prevention circuit (4, 7, 8) determines that the trip signal is caused by an inrush current from the primary voltage vp (not a fault inside the transformer). since blocked by the aND circuit ₈₁ determines, trip signal is not output from the timing circuit 9.

In the case of a fault inside the transformer, the magnetic flux φ is smaller than the set value φs and the comparator 7 does not output the trip signal.
The circuit breaker CB on the side of the transformer having an internal fault that has been confirmed by the timed circuit 9 is tripped through ₁ and the transformer having the internal fault is disconnected and protected.

Embodiment 2 FIG. 3 is a block diagram of a ratio differential relay according to an embodiment of the present invention. EOP of the ratio differential relay (4-8 ₂₎ includes an integration circuit 4 for outputting a magnetic flux phi by integrating the primary voltage vp of the transformer, a delay circuit 5 for delaying the flux phi △ time , The current magnetic flux φ from the integrating circuit 4
And a magnetic flux difference calculating circuit 6 for detecting a difference φd between the magnetic flux φ ′ from the delay circuit 5, a comparison circuit 7 for comparing the magnetic flux difference φd with a set value φds, and an output of the comparison circuit 7. and a logical product circuit ₈₁ to be input to the timing circuit 9 through a trip signal from the comparator circuit 3.

Since other configurations are the same as those in FIG. 1, the same components are denoted by the same reference numerals, and redundant description is omitted. This ratio differential relay is used as the ratio differential relays A and B for the parallel operation of the two transformers shown in FIG. 2, as in the first embodiment.

The φ-id characteristic of the transformer is as shown in FIG. 4. When an internal fault occurs in the transformer, the magnetic flux φ is small, and the φ-id characteristic is small.
The slope of the characteristic becomes large, and φ becomes large and φ−
The slope of the id characteristic becomes small. The output of the magnetic difference detection circuit 6 corresponds to the slope of the φ-id characteristic.

Therefore, in the operation of FIG.
When the other transformer TRA is energized while RB is energized, and when an exciting rush current flows through the already energized transformer TRB, the magnetic flux difference φd output from the magnetic flux difference detection circuit 6 Is smaller than the set value φds, the comparison circuit 7 does not output. Trip signal when the transformer inrush Therefore output from the comparator circuit 3 is blocked by the AND circuit _82, the trip signal from the timing circuit 9 to the breaker CB is not output.

In case of an accident inside the transformer, the transformer φ-
Since the slope of the id characteristic is large and the magnetic flux difference φd output from the magnetic flux difference detection circuit 6 is larger than the set value φds, the comparison circuit 7 outputs. Trip signal when an internal fault output Consequently from the comparator circuit 3 are Kairetsu the transformer internal fault trips the breaker CB and outputs are identified in as timing circuit 9 AND circuit ₈₂ Protect.

[0026]

Since the present invention is configured as described above, it has the following effects. (1) The malfunction of the differential relay due to the inrush current of the transformer can be prevented.

(2) The malfunction prevention circuit is simple in configuration because the magnetic flux of the transformer is obtained from the primary voltage of the transformer and the value of the magnetic flux itself is used as a criterion.

[Brief description of the drawings]

FIG. 1 is a block diagram of a differential relay according to a first embodiment.

FIG. 2 is a circuit block diagram of a parallel operation of the transformer according to the first and second embodiments.

FIG. 3 is a block diagram of a differential relay according to a second embodiment;

FIG. 4 is a φ-id characteristic diagram of a transformer.

FIG. 5 is a parallel operation circuit diagram (1) of a conventional power transformer.

FIG. 6 is a parallel operation circuit diagram (2) of a conventional power transformer.

FIG. 7 is a parallel operation circuit diagram (3) of a conventional power transformer.

FIG. 8 is a block diagram of a conventional ratio differential relay.

FIG. 9 is an explanatory diagram of an inrush current for exciting a parallel transformer bank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Current difference detection circuit 2 ... Effective value calculation circuit 3 ... Comparison circuit 4 ... Integration circuit 5 ... Delay circuit 6 ... Comparison circuit 8 ... Logic circuit A, B, T ... Ratio differential relay

Claims (3)

[Claims] 1. A differential relay for protecting a parallel transformer bank provided in each transformer, an integration circuit for integrating a voltage at a primary terminal of the transformer to obtain a magnetic flux of the transformer, and an absolute value and a set value of the magnetic flux. A circuit that blocks the output of the trip signal of the differential relay if the absolute value is large,
A differential relay for protecting a parallel transformer bank, comprising a malfunction prevention circuit comprising: 2. A differential relay for protecting a parallel transformer bank provided in each transformer, an integrating circuit for integrating a primary terminal voltage of the transformer to obtain a magnetic flux of the transformer, and a magnetic flux of the transformer from the magnetic flux. A malfunction prevention circuit comprising: a circuit for detecting that a slope of a primary current difference characteristic and a secondary current difference characteristic is smaller than a set value and preventing output of a trip signal of a differential relay. Differential relay for protection of device bank. 3. The circuit according to claim 2, wherein the circuit detects a gradient of a magnetic flux-primary-secondary current difference characteristic of the transformer smaller than a set value from the magnetic flux, and prevents output of a trip signal of the differential relay. A circuit that delays the magnetic flux from the integration circuit for a short time, a comparison circuit that compares the difference between the current value of the magnetic flux and the delayed magnetic flux with a set value, and outputs when the difference between the magnetic fluxes is larger than the set value, A logic circuit for outputting a trip signal of the differential relay on condition that there is an output of the comparison circuit.