JPH01114324A - Selective ground-fault relay - Google Patents

Abstract

PURPOSE:To promote the miniaturization of a device by providing a current transformer in the neutral point of a surge absorber. CONSTITUTION:When a ground-fault trouble is generated in a distribution line 4 providing stray capacity 6, a zero-phase current i2 from a surge absorber 7 and a zero-phase current i1 from the stray capacity 6 are allowed to flow in the distribution line in trouble. A flow of the zero-phase current i2 in a neutral point 7A of the surge absorber 7 is in the same direction toward an earth side both in a distribution line side of the ground-fault trouble and a sound circuit side, but a flow of the zero-current in its total value in a zero-phase current transformer 2 is in an opposite direction between the distribution line side of the ground-fault trouble and the sound circuit side. Since a selective earth protecting relay 3 operates only when it is in a direction of the zero-phase current i1, the distribution line 4 in the ground-fault trouble can be disconnected by breaking a switch 1. Thus because the flow of current is only through an earth line of the neutral point, the zero-phase current can be detected only by additionally providing a small current transformer, accordingly simplifying structure of a device, its miniaturization can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a directionally selective ground fault relay bag for a high voltage ungrounded system.

[Conventional technology]

Conventional devices employ a method of detecting zero-sequence voltage using a grounded instrument transformer or a zero-sequence capacitor, as described in Japanese Patent Application Laid-Open No. 60-261324.

[Problem that the invention seeks to solve]

In the above conventional technology, a grounded instrument transformer, a zero-phase capacitor, etc., are installed in a closed switchboard for zero-phase voltage detection, but this requires storage space, and the grounded instrument transformer, zero-phase capacitor, etc. This has the disadvantage that the device becomes bulky due to the need for its own protective device and the like.

An object of the present invention is to provide a selective ground fault relay device that is miniaturized.

[Means for solving problems]

The above purpose is to be a component of a 1-selection earth fault protection relay device,
The purpose is achieved by providing a current transformer at the neutral point of the surge absorber as one of the input elements of the selective earth fault protection relay and inputting the secondary current of this current transformer.

[Effect]

When a ground fault occurs in the system, a zero-sequence voltage is generated in the system, and this zero-sequence voltage causes a zero-sequence current to flow to the neutral point of the surge absorber. This zero-sequence current is converted to an appropriate magnitude as a relay input by a current transformer installed at the neutral point of the surge absorber.

Input to selective earth fault protection relay. On the other hand, the ground fault current flowing to the ground fault point is input to the selective ground fault protection relay by a zero-phase current transformer provided in the main circuit cable. This 2
By comparing the phases of the two currents, the relevant ground fault point can be detected and removed. Thereby, the spread of the failure can be minimized.

〔Example〕

FIG. 1 shows an embodiment of the invention.

A switch 1 is connected to the transformer, and a surge absorber 7 is installed on the load side of the switch 1 to absorb surges generated from the switch 1, and a neutral grounding wire 7A is installed on the load side of the switch 1. A current transformer 8 is provided, and the secondary side of the current transformer 8 is connected to the selective earth protection relay 3 . On the other hand, the secondary side of the zero-phase current transformer 2 provided in the main circuit cable IA for the purpose of detecting a ground fault current is also connected to the selective ground fault protection relay 3. In addition, the distribution line 4.5 on the load side of the zero-phase current transformer 2
has a stray capacitance of 6. There is a stray capacitance of 6.

When a ground fault occurs in the distribution line 4, the zero-sequence current from the surge absorber 7 and the zero-sequence current ix from the stray capacitance 6 of the distribution line flow into the faulty distribution line 4 through the ground fault point.
Here, the direction of the zero-sequence current iz flowing to the neutral point 7A of the surge absorber 7 is the same on both the distribution line side where the ground fault has occurred and the healthy line side, and it flows into the ground side. However, the direction of the total value of the zero-sequence current flowing through the zero-sequence current transformer 2 is opposite on the distribution line side where the ground fault has occurred and on the healthy line side. Selective ground fault protection relay 3
operates only when the direction is the zero-sequence current 11 in FIG. As a result, the relevant switch 1 is shut off, and the ground fault distribution line 4 can be disconnected.

FIG. 2 also shows another embodiment of the present invention, in which the current transformer 8 provided at the neutral point of the surge absorber 7 and the zero-sequence current detected by the zero-sequence current transformer 2 cause the selective earth fault protection relay 3 This relay can interrupt the switch 1 and disconnect the ground fault on the load side of the zero-phase current transformer 2.

〔Effect of the invention〕

As described above, according to the present invention, the current transformer installed at the neutral point of the surge absorber passes only the grounding wire at the neutral point, so the grounding wire has no potential and is thin. Because it is a grounding wire, zero-sequence current can be detected by simply adding a small current transformer that does not have problems such as insulation, so the structure of the selective grounding relay device can be simplified and downsized.

In addition, the surge absorber is installed on each distribution line and uses its neutral point, so the selective ground fault protection device can be separated for each distribution line, so it is not affected by other lines. A highly reliable protection device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a selective ground fault relay device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a main part of a selective ground fault relay device showing another embodiment of the present invention. 1...Switch, 2...Zero-phase current transformer, 3...Selective earth fault protection relay, 4...Ground fault faulty distribution line, 5...Sound distribution line, 6...Distribution line Stray capacitance of electric wire, 7...Surge absorber, 8...Current transformer. Agent Patent Attorney Katsuri Ogawa -6,

Claims (1)

[Claims] 1. Connect the main circuit cable to the three-phase bus, install a switch and zero-phase current transformer on the main circuit cable, install a surge absorber branching off from the main circuit cable, and install a neutral point grounding wire on the surge absorber. A selective earth fault protection relay, which opens a switch using a selective earth fault protection relay operated by the detected current of a current transformer and a zero-phase current transformer provided in a neutral point grounding wire. Relay device.