JPS61269609A - Protective relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a protective relay, particularly a protective relay for a power system, and more particularly, it is used in combination with a current transformer to handle a relatively small overcurrent to a large short circuit current. This invention relates to a protective relay for power systems that can perform suitable detection.

[Background of the invention]

As shown in Figure 1, overcurrent relays used in high voltage, large current power systems generally have a large tf of high voltage main circuit l.
A time-limiting relay coil 3 for detecting a small current and an instantaneous relay coil 4 for detecting a large current are connected in series on the secondary side of a current transformer 2 that converts i into a small current l.

That is, a small current due to an overload in the power system is detected by the time-limited relay coil 3, and a large current due to a short circuit is detected by the instantaneous relay coil 4.

In this way, overload and short-circuit accidents in the power system are detected, and a trip command is given to the circuit breaker 5 to open the circuit breaker, thereby protecting the power system.

In the configuration shown in FIG. 1, generally the time-limiting relay coil 3
In order to detect a small current, the impedance is large because many thin wires are wound.On the other hand, the instantaneous relay coil 4 detects a large current, so there is no need to increase the number of windings, and its impedance is large. Impedance is small〇 As mentioned above, since two coils with different impedances are connected in series, the impedance on the secondary side of current transformer 2 is high.0 As is obvious in conventional protective relays, It is necessary to configure the circuit so that a large current that can be detected by the instantaneous relay coil 4 flows in a circuit with such high impedance in the event of a short-circuit accident.As shown in the equivalent circuit in Figure 2, the current The secondary current of the transformer 2 is shunted at the inverse ratio of the value of the CT excitation impedance 8 and the impedance of the sum of the impedance 9 of the time-limited relay coil 3 and the impedance 10 of the instantaneous relay coil 4 connected in parallel to the CT excitation impedance 8. do.

In order to send a large current to the instantaneous relay coil 4 connected in series with the time-limiting relay coil 3 having a large impedance, a current transformer with a large CT excitation impedance,
In other words, a large and expensive current transformer with a high saturation voltage is required.

In addition, if a current transformer 2 with a high saturation voltage is used, when a large current flows in the high voltage main circuit l due to a short circuit, etc., a voltage higher than the standard withstand voltage of the secondary circuit of the current transformer 2 will occur. However, there is a risk of dielectric breakdown.

Furthermore, since the two coils are connected in series, if one of the coils is disconnected, the secondary side of the current transformer g%2 becomes open, and abnormal voltage occurs on the secondary side of the current transformer 2. However, there is a risk of dielectric breakdown of the secondary circuit.

[Purpose of the invention]

An object of the present invention is to achieve a good protection function for a high-voltage main circuit by connecting a time-limiting relay coil and an instantaneous relay coil in parallel, without requiring an expensive current transformer with large excitation impedance or saturation voltage. An object of the present invention is to provide a protective relay for a power system that can be used in a power system.

[Summary of the invention]

The present invention connects a series connection circuit of an instantaneous relay coil and an arrester in parallel with the time-limited relay coil, so that a small current flows only through the time-limited relay coil, and a current exceeding a certain value flows through the time-limited relay coil. When the voltage across the time-limiting relay coil exceeds the discharge voltage of the arrester, the arrester discharges, causing a large current to flow through the instantaneous relay coil with low impedance, and the current transformer is activated. The feature is that the saturation voltage and excitation impedance can be made small. [Embodiments of the Invention] A typical embodiment of the present invention will be described below with reference to FIG. 3. In the figure, the same reference numerals as in FIG. 1 represent the same or equivalent parts.

As shown in FIG. 3, the overcurrent relay in the power system includes a time-limiting relay coil 3 having a large impedance for detecting small currents and a small impedance coil for detecting large lightning in the secondary circuit of the current transformer 2. The instantaneous relay 4 and the series circuit of the arrester 6 are connected in parallel.

The current of the high voltage main circuit 1 is about 1 to 2 times the rated current,
In the range of relatively small overcurrent, time relay 1 is used and coil 3
The voltage across the voltage is small and is below the discharge voltage of the arrester 6. Therefore, the current flows through the secondary of the current transformer 2 only to the time-limiting relay coil 3.

However, the current of the high voltage main circuit 1 is 10 to 2 times the rated current.
When the short circuit current reaches 0 times, which is a large short-circuit current, the voltage across the time-limited relay coil 3 increases, causing the arrester 6 to discharge. Therefore, due to the inverse ratio of the impedance values of the time-limited relay coil 3 and the instantaneous relay coil 4, A large current flows through the instantaneous relay coil 4.

That is, according to this embodiment, '1' of the high voltage main circuit 1
When the current 11c is small, the secondary current of the current transformer 2 flows only through the time-limiting coil 3, which has a large impedance.
When a large current flows in the high voltage main circuit 2, mainly
A large current begins to flow through the instantaneous relay coil 4, which has a small impedance.

As described above, according to this embodiment, since a large current is not passed through the time-limiting relay coil 3 having a large impedance, the current transformer 2 does not require a high saturation voltage.In other words, the current transformer 2 is small and inexpensive. can be made into something.

Moreover, since the saturation voltage of the current transformer 2 is low, even if a large amount of lightning flows through the high voltage main circuit l, there is no risk of high voltage being generated in the secondary circuit of the current transformer 2.

Furthermore, since the two coils are connected in parallel, even if one coil is disconnected, high voltage generation and dielectric breakdown of the secondary circuit due to an open circuit in the secondary circuit of the current transformer 2 can be prevented. Therefore, there is also the effect that the reliability of the protective relay can be improved.

Incidentally, in the present invention, it is of course possible to use a suitable constant voltage discharge device instead of the arrester 6.

〔Effect of the invention〕

According to the present invention, the saturation voltage and excitation impedance of a current transformer used in combination with a protective relay can be reduced, so the current transformer can be made smaller and cheaper, and furthermore, insulation breakdown due to high voltage in the secondary circuit of the current transformer can be reduced. can be prevented.

Furthermore, it is possible to prevent the occurrence of abnormal voltage caused by an open circuit in the secondary circuit of the current transformer due to disconnection of the relay coil, which has the effect of improving the reliability of the protective relay.

[Brief explanation of the drawing]

Fig. 1 is a route diagram that does not show a conventional power system protection relay, Fig. 2 is a circuit diagram showing the same circuit as shown in Fig. 1, and Fig. 3 is a route diagram showing the configuration of one implementation train of the present invention. be.

Claims (4)

[Claims] (1) In a power system protective relay comprising a current transformer coupled to a main circuit, and a small current detection coil and a large current detection coil connected to a secondary circuit of the current transformer, the above-mentioned 2 Two current detection coils are connected in parallel,
A protective relay characterized in that a constant voltage discharge device is connected in series to the large current detection coil. (2) The protective relay according to claim 1, wherein the small current detection coil is a time-limited relay coil. (3) The protective relay according to claim 1, wherein the large current detection coil is an instantaneous relay coil. (4) The protective relay according to any one of claims 1 to 3, wherein the constant voltage discharge device is an arrester.