JPH08168165A - Protective relay for transformer - Google Patents

Abstract

PURPOSE: To prevent unnecessary functions of a ratio differential relay when it is employed for protecting a transformer. CONSTITUTION: The protective relay for a transformer comprises current transformers 2A, 3 disposed, respectively, on the input side and output side of a transformer 1 to be protected, and a ratio differential relay element 2 which functions when the ratio between the differential current of both current transformer and a suppression current exceeds a predetermined value, wherein a circuit breaker 7 connected with the load side of the transformer 1 is tripped by an output from the ratio differential relay element 2 thus protecting the transformer. A ground fault overcurrent relay 4 is provided on the secondary of a load side transformer while a ground fault overvoltage relay 6 is provided on the secondary of a voltage transformer 5. AND of the NOT output from the ground fault overvoltage relay and the output from the overcurrent relay is employed as a lock signal for the ratio differential relay element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective relay device for a power transformer using a ratio differential relay, and more particularly to a protective transformer device for preventing unnecessary operation when a current transformer is saturated. Regarding electronic devices.

[0002]

2. Description of the Related Art A ratio differential relay (a relay for internal failure of a transformer) shown in FIG. 3 is a secondary current I1 of a power source side current transformer CT1 provided in a transformer 1 to be protected and a load side transformer. The difference between the secondary currents I2 of the transformer CT2 (differential current) is taken, and the internal failure of the transformer 1 is determined by the DIF element (differential current determination circuit). In the DIF element, the current transformer CT1 and the current transformer CT2
If the input currents I1 and I2 that have passed through are properly matched in the transformer 1 at the time of normal operation or at the time of external failure, I1-I2 = 0 and no difference current is generated.
Should a failure occur inside the transformer 1, the current will be out of balance and a differential current of I1-I2 will occur. When this difference current satisfies the conditional expression which is the difference current determination circuit of the DIF element, "1" is output, and the 2F-LOCK element (the second harmonic of the difference current of I1-I2 is generated when the transformer inrush current is present). Current I
2f and the fundamental wave current I1f are detected, the content rate of the second harmonic with respect to the fundamental wave current is detected, and when the content rate exceeds a certain value, it operates, and outputs "0" to the NOT circuit,
When the AND condition is satisfied by the logical product of the AND circuit with the output that locks the ratio differential relay), the circuit breaker (not shown) is tripped.

[0003]

When the transformer connected to the load side of the protection target transformer 1 is turned on, an exciting inrush current flows in the transformer connected to the load side. The excitation inrush current contains a relatively large amount of DC component, second harmonic, third harmonic, fourth harmonic, and fifth harmonic. The transformer 1
The DC component included in the exciting inrush current generated when the transformer on the load side is repeatedly turned on is not removed when the transformer on the load side is repeatedly turned on. Since the DC component remains in the transformer, the transformer 1
In any of the current transformers, even if some of the current transformers become demagnetized or saturated and an imbalance occurs in the secondary circuit of the current transformer, the transformer 1 does not have an internal failure. Nevertheless, a differential current is generated inside the ratio differential relay, and the ratio differential relay operates unnecessarily.

Therefore, an object of the present invention is to combine a ratio differential relay (2F-LOCK element), a ground fault overcurrent relay, and a ground fault overvoltage relay to cause unnecessary operation due to the DC component remaining in the load side current transformer. An object of the present invention is to provide a transformer protection relay device for the purpose of preventing this.

[0005]

In order to achieve the above-mentioned object, the present invention has a constitution as shown in FIG. 1, in which a power source side change is connected by a triangle for a current element detector on the power source side of a transformer 1. The downstream side of the load side current transformer 3 and the ground fault overcurrent relay 4 connected to the current transformer 2A, the load side current transformer 3 connected in a star shape for current detection on the load side of the transformer. A ground fault overvoltage relay 6 connected to an instrument transformer 5, a circuit breaker 7 connected downstream of the instrument transformer 5, and a transformer 8 connected below the circuit breaker 7. It is characterized by having.

[0006]

In the above structure, the unnecessary operation of the ratio differential relay 2 in the biased state or the saturated state of the load side current transformer 3 caused by the exciting inrush current generated from the transformer 8 due to the repeated closing of the circuit breaker 7. Can be prevented.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an internal block diagram of a ratio differential relay 2 for explaining the operation of FIG.

In FIG. 1, 1 is a transformer to be protected, 2 is a ratio differential relay, 2A is a power source side current transformer, 3 is a load side current transformer, and 4 is a ground connected to a load side current transformer. A fault overcurrent relay, 5 is an instrument transformer, 6 is a ground fault overvoltage relay connected to the instrument transformer 5, 7 is a circuit breaker, and 8 is a transformer.

In the above structure, the ratio differential relay 2 of the transformer 1 is inoperative, the ground fault overcurrent relay 4 is inoperative,
The ground fault overvoltage relay 6 does not operate, and the circuit breaker 7 above the transformer 8 is open.

When the circuit breaker 7 is repeatedly turned on, an exciting inrush current flows through the transformer 8, and a direct current component included in the exciting inrush current is connected to the load side of the transformer 1 on the load side. Part of the current transformer 3 remains, and the load-side current transformer 3 is biased or saturated. When the magnetic field is not biased or saturated, it is zero at the neutral point of the load side current transformer 3 connected to the load side, but when it is biased or saturated due to the DC component, the load connected to the load side. It does not become zero at the neutral point of the side current transformer 3. While the apparent zero-phase current flows and the ground fault overcurrent relay 4 operates, the instrument transformer 5 for detecting the power system failure
Since no ground fault has occurred in the system, the ground fault voltage is not generated and the ground fault overvoltage relay 6 becomes inoperative. When the ground fault overcurrent relay 4 is in operation and the ground fault overvoltage relay 6 is not in operation, the load side current transformer 3 is biased or saturated due to the DC component, so that a differential current is generated inside the ratio differential relay. . In this case, in order to prevent the ratio differential relay 2 from operating, the output of the ground fault overcurrent relay 4 and the output of the NOT circuit of the ground fault overvoltage relay 6 are used as the output of the AND condition “1” as shown in FIG. The 2F-LOCK element output and the NOR circuit lock the ratio differential relay 2. At the time of a normal power system failure and an internal failure of the transformer 1, both the ground fault overcurrent relay 4 and the ground fault overvoltage relay 6 operate, so the AND condition output of the ground fault overcurrent relay 4 and the ground fault overvoltage relay 6 is “0”. Therefore, the ratio differential relay 2 is not locked, and unnecessary operation of the ratio differential relay 2 due to the DC component of the load side current transformer 3 can be prevented.

As shown in FIG. 2, the ratio differential relay 2 incorporates the operation / non-operation signals of the ground fault overcurrent relay 4 and the ground fault overvoltage relay 6 into a logic circuit as shown in FIG. If incorporated, the operation of the ratio differential relay 2 can be locked.

According to the present invention, the logical product of the ratio differential relay 2 and the operation outputs of the ground fault overcurrent relay 4 and the ground fault overvoltage relay 6 is added, whereby the load side transformer due to the DC component generated in the load side transformer 3 is added. It is possible to prevent unnecessary operation of the ratio differential relay 2 due to the demagnetization and saturation of the current transformer 3.

[0013]

As described above, according to the present invention, by combining the ground fault overcurrent relay 4 and the ground fault overvoltage relay 6, the DC component remaining in the load side current transformer 3 is brought into a biased state and a saturated state. Ratio differential relay 2 due to load side current transformer 3
It is possible to provide a highly reliable transformer protection relay device capable of preventing unnecessary operation of the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram for explaining the operation of the present invention.

FIG. 3 is a block diagram of a conventional device.

[Explanation of symbols]

 1 ... Transformer to be protected 2 ... Ratio differential relay 2A ... Power supply side current transformer 3 ... Load side current transformer 4 ... Ground fault overcurrent relay 5 ... Instrument transformer 6 ... Ground fault overvoltage relay 7 ... Circuit breaker 8 ... Transformer

Claims (1)

[Claims] 1. A current transformer provided on an input side and an output side of a transformer to be protected, and a ratio differential relay which operates when a ratio of a difference current and a suppression current of the both current transformers is a predetermined value or more. In the transformer protection relay device, which has an electric current element and trips a circuit breaker connected to the load side of the transformer for protection by the operation output of the ratio differential relay element, An earth fault overcurrent relay is provided on the secondary side of the transformer, and a ground fault overvoltage relay is provided on the secondary side of the voltage transformer for detecting the load side voltage of the transformer, and the operation output of the ratio differential relay element and the ground are provided. And a circuit for obtaining a logical product of an operation output of the ground fault overvoltage relay and an operation output of the ground fault overcurrent relay by an AND circuit, and tripping the circuit breaker when an AND condition is satisfied. Transformer protection relay device.