SU410511A1 - - Google Patents

Description

one

This device relates to generators protection against earth faults, operating wiring, which contains voltage transformers, a source of superimposed alternating current frequency, a multiple of the generator frequency, three-transformer zero-sequence current filters, and an execution relay.

In order to increase reliability and sensitivity, common points of three phase current transformers connected in a pair of secondary windings, forming a zero-sequence current filter, are connected to a voltage transformer via a frequency multiplier, and the output of the specified filter is connected to one of the magnetic amplifier inputs with an executive output relay whose other input is connected to a frequency multiplier.

The drawing shows a schematic diagram of the protection of the generator against earth faults.

The circuit includes a double filter of zero-sequence currents 1, a three-phase voltage transformer 2, a converter (multiplier) of frequency 3, a relay of overcurrent 4, for example, type RT-40, a relay of overcurrent 5, for example, type ETD551, magnetic power amplifier 6, rectification bridge 7, filter 8, frequency 100 or 25 Hz.

Generator zero-sequence currents are measured using filter 1 consisting of a pinch of identical two-winding transformers. The low voltage windings of these transformers combine the functions of bias and secondary windings. The windings of each phase are connected in series - consistently, and the opposite conclusions - in neutral points. The common points of the windings of the three phases are connected through a frequency multiplier 3 to a voltage transformer 2, from which

magnetization The primary circuits of the transformers are not magnetically connected to the bias circuit. The frequency of the bias current is chosen depending on the specific parameters of the transformers, but it must be different from the frequency of the applied current at which the protection operates.

In order to eliminate the residual magnetic flux, the magnetization induction somewhat exceeds the induction generated in the cores of the transformers by the primary current under short-circuit conditions. This requirement is facilitated by the fact that the ampere turns of the bias currents are completely consumed to create magnetic fluxes in the core magnetizations.

transformers, while the magnetizing flux is created by only a small part of the ampere-turns of the primary current of the forward or reverse sequence, since they are mainly balanced by the ampere-turns of the secondary currents, trapped, in their small resistance windings of the transformers. The number of turns and the cross section of the wire of the secondary windings of the transformers are chosen so that the induction of the biasing is about 0.3-0.4 T and the induction from the short circuit current is slightly less.

In dissecting the neutral wire, connecting it, its neutral points of the transformer windings are connected through a frequency filter 8, a rectifying bridge 7 and a magnetic amplifier 6, the main sensitive relay 5. The amplifier 6 is also powered from frequency multiplier 3 together with a filter biasing circuit 1. Under normal conditions, the neutral wire is surrounded only by the unbalance current of the filter, and the current in relay 5 is practically zero. For all types of damage outside the zone, the current in relay 5 is also approximately zero. In the event of a ground fault in the stator of the protected generator, the relay 5 flows around straightened and amplified superimposed current, part of which is 100 or 25 Hz.

Used in the protection scheme, the 6 transformer filter of zero-sequence currents was studied experimentally on a reduced physical model.

In addition to the above elements of the device zadlity from single-phase earth faults, in the scheme under consideration is also provided the usual protection against double earth faults using a relay 4, acting on the generator off without time delay.

Subject invention

Device for protection against short circuits

ground bus generators containing a source of superimposed alternating current frequency, a multiple of the generator frequency, a voltage transformer, zero sequence current transformer filters, and an executive relay, characterized in that, in order to increase reliability and sensitivity, common points are connected in pairs and series of secondary windings of current transformers of three phases, forming a zero sequence current filter, are connected via a frequency multiplier with a voltage transformer, and the output of the decree through a frequency filter and a rectifier bridge connected

to one of the inputs of a magnetic amplifier with a magnetic relay output, the other input of which is connected to a frequency multiplier.