SU911378A1 - Apparatus for detecting single-phase earthing in compensated-neutral networks - Google Patents

Description

 , The invention relates to electrical measuring equipment and can be used to determine the location of a ground fault in a power cable in networks with compensated neutral.

A device for determining the location of a ground fault in a power cable is known, which contains an alternating current source connected between the earth and the damaged phase tl.

The disadvantage of the device is low accuracy.

The closest in technical essence is a device comprising a zero-sequence current transformer, an actuating element, a current sensor, a pointing element and a phase detector 2.

The disadvantage of this device is the ability to detect only the line with damage, and not the location of damage.

The purpose of the invention is to improve accuracy.

This goal is achieved by the fact that a selective filter and a source of reference voltage are introduced into the device for finding a single-phase earth fault in networks with a compensated neutral, containing a zero-sequence current filter, a phase detector and an indicating element, and zero sequence connected to

10 by the input of a selective filter, the output of which is connected to the first input of the phase detector, the second input of the last filter is connected to the output of the reference voltage source, and the output to the indicating element.

FIG. 1 shows a network diagram with compensated neutral; in fig. 2 is a block diagram of the proposed device; in fig. 3 is a plot of the dependence of the floor-distance intensity and the angular frequency.

The device contains a filter 1 zero-sequence currents, F39

the detector 2, the pointing element 3, the selective filter k, the source 5 of the reference voltage.

The device works as follows.

When compensating for the capacitive current of the earth fault by superimposed inductive current, there is a resultant field generated by the currents in the cable above the cable route, and inductive and capacitive currents flow to the damage site and at the damage point the resulting current changes phase by J.

Residual current components at the point of closure l

WITH,,

OST - y-.

S

OK

YOU- phase voltage. B, B;

Where

capacitance, which determines the value of capacitive current, μF;

X, .inductive impedance of the circuit, which determines the value of the compensating TOKZ, Ohm.

At the earth fault, residual current per component 13 wasps. 33gj) is minimal and changes phase by J.

When driving over a cable route with damage {FIG. For) capacitive and inductive currents flow to the site of damage from the source of power, and capacitor toKM from the side of the consumer, therefore, when measuring the voltage of the floor above the cable route, the zero-order filter 1 phase of the Reverse signal relative to the reference voltage from the source 5 with synchronizing the device will be determined by the value of the equivalent parameter in the chain of INDINCTION or capacitance. When compensating for capacitive current, this signal will be inductive. On phase

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Detector 2 is supplied with two signals — from a selective filter that allows to be rejected from the noise field, and a source 5 of the reference voltage synchronized with the network. When passing through a cable closure (.6), the measured field (zero sequence current in the cable) will be capacitive, will change phase to L, which is detected by phase detector 2 connected to index element 3

The use of the proposed facility allows finding the place of the earth fault without disconnecting consumers, shortens the search time and damages from damage.

Claims (2)

1.Chernsnbrovov N.V. Relein protection. M., Energie, 197, p. . 2. USSR author's certificate number 696568, cl. GiOl 31/08, 1977 (prototype).