SU970552A1 - Device for differential protection of converter - Google Patents

Description

The invention relates to electrical engineering and can be used in the differential protection circuit of high-power converters against valve switching disturbances, for example, in DC power transmissions.

Devices are known for blocking or detuning the differential protection of a converter from surges in the secondary current of electromagnetic direct current transformers, which are an additional arm in the differential protection circuit, made on an additional intermediate current transformer and several rectifying bridges 1,

The disadvantages of these devices are the complexity of the circuit and the degradation of the protection characteristics. In addition, device 5 has not achieved absolute detuning with doubled bursts of DC transformers,

The closest in technical essence to the present invention is a device for differential protection of a converter, comprising a transreactor, a reacting organ, an AND element and sensors of phase and rectified currents, forming the circuit

comparison, in the differential branch of which are included serially connected transreactor and reacting organ 21.

The disadvantage of this device is the low speed due to the presence of time delays in the blocking circuit.

The purpose of the invention is to increase

10 speeds.

The goal is achieved by the fact that the device is equipped with a pulse expander, diodes and an additional transreactor, and

15 The input of the additional transreactor is connected in series with the sensor of the phase current and the output of the additional and main transreactors are connected via diodes to the element I,

20, the output of which is connected to the control input of the reacting body through a pulse expander.

FIG. 1 shows the scheme of the proposed device; in fig. 225 timing diagrams explaining the operation of the device in case of violation of the switching of the rectifier (NKV) of the rectifier and during current surge TFT.

Device for differential

The converter protection 30 contains a sensor 1 for phase currents and a sensor 2 for rectified current, in the differential branch of the phase rectified currents comparison circuit a transactivator 3 a in the arm of the phase currents of the comparison circuit an additional transceiver 4, the secondary windings of which are connected to the inputs through dith 5 element And 7, the output of which through the expander 8 pulses connected to the reacting authority 9.

The device works as follows.

With an NF converter (Fig. 2), a current pulse ig in the differential protection branch appears with a simultaneous decrease in arm current ij. This simultaneity of arm current reduction from phase current transformers (CT) and the current occurrence in the differential protection branch is used in as a reliable and stable characteristic of the NF to generate a signal that permits the action of the reacting organ 9. To generate a resolution signal using diodes 5 and b, the secondary voltage pulses of transreactors 3 and 4 corresponding to a decrease in t an eye

ctii

 o for transreactor 4

1 shoulder

at

increase the current igC - 0) for

dt

of the transreactor 3, With the NFR, these pulses coincide (Fig. 2a) and a signal appears at the output of the And 7 element. At the output of the expander 8 pulses, the duration of this signal is longer and sufficient to trigger the reacting authority 9 of the protection.

When current spikes TFT change the current ij shoulder. TT and differential current io. Are the same (fig, 25), since current bursts of TFT branch out into the TT protection arm and into the differential branch. The currents ij and i simultaneously increase and decrease. Therefore, pulse signals from the secondary windings of transreactors

3 and 4 in time do not match. At the output of the element And 7 and the expander 8 pulses with current TTP spikes, the enabling signal does not appear, i.e. the action of the reacting authority 9

0 is blocked.

Thus, due to the introduction of an additional transreactor, the proposed device has a higher speed.

Claims (2)

1. To produce universities. Energy, 1976, 1, p. 15-21. 2. Author's certificate of the USSR 7Q2921, cl. H 02 H 7/10, 1978. Ptff.1  IT / TS . -TO I, ij r M11-I  I i / f2