SU817841A1 - Device for differential protection of transformer - Google Patents

Description

(54) DEVICE FOR DIFFERENTIAL PROTECTION OF THE TRANSFORMER

The input of the harmonic filter is connected to the output of the secondary signal converter, the signal of which is proportional to the differential current of the phase under consideration, the output of the 1-; rntrol current body to the corresponding brake input of the reacting body, and the measuring inputs of the current control body are connected to the outputs of the secondary signal converter whose signals are proprinated shoulder protection currents.

FIG. 1 is a block diagram of a device for transformer differential protection; in fig. 2 - dependence of the brake signal of the reacting organ on the magnitude of the high harmonic currents. The device contains current transformers 1, the outputs of which are connected to the converter 2 secondary signals. The outputs of the converter 2 of the secondary signals are connected to the reacting body 3 and the unit 4 of the detuning from magnetizing current surges, the output of which is connected to the corresponding brake input of the reacting body 3. In addition, the output of the secondary converter 2, the signal of which is proportional to the differential phase current, is connected to a filter 5 high harmonics. The output of the high harmonic filter 5 is connected to the rectifier 6. The output of the rectifier 6 is connected to the nonlinear converter 7. The output of the nonlinear converter 7 is connected to the current control unit 8, the measurement inputs of which are connected to the outputs of the converter 2 secondary signals whose signals are proportional to the currents of the protection arms. The output of the current control body 8 is connected to the corresponding brake input of the reacting body 3. The high harmonic filter 5, the rectifier 6, the nonlinear converter 7 and the current control body 8 constitute the overstimulation deceleration unit 9. The output of the reacting organ 3 is the output of the device.

The device works as follows. During normal operation and when the coil closures x, when the induction of the transformer is close to or below the nominal, the harmonic current in the differential circuit does not exceed. Therefore, during winding closures, the block 9 of deceleration during overexcitation does not cause additional delays in response, since the signal at the output of the high harmonics filter 5 is absent or has such a magnitude that the nonlinear converter 7 operates with a minimum transmission coefficient and practically does not issue a brake signal to the responding organ 3. Due to this, the protection performance is maintained when the closure of a small number of turns of the transformer to be protected.

When closing a large number of turns of the protected transformer,

Higher harmonics in the differential current may increase due to the faults in the operation of current transformers 1, which are particularly large in a transient mode. As the increase in brake signal leads

to an increase in the protection response current, the response time may increase due to the reduction in the multiplicity of the useful signal. Therefore, with currents in the arms of protection exceeding the sum of the value corresponding to the maximum load current and the magnitude of the initial response current of the protection, the braking signal from the deceleration braking unit 9 is limited by the current control authority 8, which allows the protection performance to be maintained during short circuits the number of turns of the protected transformer.

In case of short circuits in the protection zone, the faults of current transformers 1 in the transient mode are especially large, which can lead to considerable delays

in the operation of the protection due to the decrease in the useful signal of the relay and significant deceleration, due to the operation of the unit 4 of the detuning from magnetization current surges. Moreover, there is no need for additional braking from the braking unit 9 during over-excitation in the mode of external short circuits, since the protections have means for detuning from unbalance currents. Therefore, at any overcurrent, the current control body 8 completely removes the braking

0 signal, which allows to preserve the protection performance during internal short circuits.

When the power transformer is over-excited, when the induction in its core significantly exceeds the nominal and the content of high harmonics in the differential current is 50%, the signal at the output of the high-harmonic filter 5 reaches a value such that the transfer coefficient of the nonlinear converter 7 increases, increasing the braking signal on the reacting body 3 (Fig. 2), which provides for selective operation of the protection during overstimulation. In this case, the average value of the rectified current at the terminals of the protected transformer at

5 levels of arcing voltage does not exceed 1.5 1 ".r and current control body 8 does not work, allowing braking.

Thus, the device allows to increase the selectivity of protection during overstimulation while maintaining its speed in the case of phase-by-phase protection.

Claims (2)

1. USSR author's certificate according to application no. 2619108 / 24-07, cl. H 02 H 3/28, 1978. 2. USSR author's certificate number 649086, cl. H 02 H 3/28, 1977. Bbixoff (rig 2 i-ffir