SU391675A1 - DEVICE FOR PROTECTION AGAINST SHORT CIRCUITS - Google Patents

Description

one

The invention relates to a relay protection technique and is intended to protect three-phase overhead networks with a neutral wire, for example, 04 kv, from single-phase short circuits.

The known protection devices (fuses and automatic switches) do not provide the necessary sensitivity to such short circuits and selectivity.

In order to increase the sensitivity when the operating current of the load is asymmetrical and suction, a transformer current sensor is connected to the neutral grounding circuit of the power transformer up to the point of connection of the neutral conductor.

On f | ig. Figure 1 shows a schematic diagram of a 10 / 0.4 kV transformer station with two outgoing lines; in fig. 2 is a schematic diagram of the protection device.

In the diagram {FIG. 1): I, 3 — current sensors installed on outgoing lines x 0.4 kV;

3- current sensor mounted on the grounding wire of the power transformer;

4- power transformer neutral grounding resistor; 5 - repeated resistors of the neutral wire.

During normal operation of the network emf. on the secondary windings of the current sensors / and 2 are close to zero, and on the current sensor 3 is equal to nude.

In case of a ground fault, the emf in the sensor, the damaged line is determined by the magnetizing force from the total current of the circuit and its fraction flowing in the opposite direction along the neutral wire, and in the sensors of the intact lines only from the share of the current flowing through the neutral wire. These ws EI and EZ will be out of phase. Comparison of the emf. on the damaged and intact lines with the reference signal), taken from the sensor installed on the ground by the junction of the power transformer, but the phase can be identified the damaged line.

The protection device {FIG. 2) contains phase-matching circuit 6 and an independent or minimal release of circuit breaker 7.

The proposed device can be implemented as a set-top box for automatic switches.

The device was experimentally tested in the laboratory on a network model.

Using the proposed device for protection against single-phase short circuits of the form phase-to-ground in aerial networks x 0.4 kV increases the reliability of power supply and the operation of low-power transformers of 10 / 0.4 kV. often out of order from such

emergency modes, and also provides electrical safety.

Subject invention

A device for protection against short circuits in three-phase networks with a zero wire and a grounded neutral, containing a measuring element — a differential filter of zero-sequence currents;

the output of which through the phase-matching circuit is connected to an executive unit, characterized in that, in order to increase the sensitivity when unbalancing the load current and suction, into the neutral circuit of the power transformer to the point pr, ac (E, the single neutral wire turns on Reformator current sensor, output. cr. p; p0 is connected to one of the inputs of phaser, avniB.uyuschego circuit.

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