SU1274054A1 - Device for differential protection of transformer - Google Patents

Abstract

The invention relates to the field of electrical engineering, in particular, to relay protection of electrical systems. used to protect transformers. The aim of the invention is to improve the speed and simplification of the device. The goal is achieved by introducing into the device a block 4 forming a brake signal consisting of successively connected high-pass filter 5, a second rectifier 6 and a smoothing circuit 7. In this case, the signal at the output of the smoothing circuit 7 provides for the formation of pauses during the duration of the comparator 8 8 10 ms At the output of element 9, the time delay for the return also occurs § a pause and the element of time delay 10 does not work. 3 il. W 4 About SP 4

Description

Phie, 1 The invention relates to electrical engineering, namely, relay protection of electrical systems, and can be used to protect transformers. The purpose of the invention is to increase the speed and simplify the device for differential protection of a transformer. FIG. 1 shows a block diagram of a pre-lagged device; in fig. 2 - current curves in case of short circuit (SC) in the protected zone; in fig. 3 - the same with a periodic surge current magnetization. The device contains a matching and correction link 1, the output of which includes the first rectifier 2, the output of the latter includes a resistor 3, a brake signal generation unit 4, the high-pass filter 5 connected in series, the second picker 6 and a smoothing circuit 7 connected in series to the comparator 8 , the return time delay element 9, the time delay element 10 and the output element 11. The high-frequency filter input is connected in parallel to the first rectifier 2 of the operating circuit, and the comparator input 8 is parallel to the output Ladies of the working circuit, smoothing circuit 7 and block 4 of the formation of the brake signal. The polarities of drivers 2 and 6, as well as the rectifier included in block 4 of the brake signal generation unit, were received so that the signal from the output of rectifier 2 was directed to the operation of the comparator 8, the signals from the outputs of rectifier 6 and The braking signal generating unit 4 was sent to return the comparator 8. I The matching 1 and corrective link 1 serves to correct the shape of the secondary current curve of high-voltage current transformers (not shown). It can be performed both on the transreactor and with the use of active elements, for example, operational amplifiers. Braking sig formation unit 4

The module performs summation of the modules of instantaneous currents of the arms of the protection, the straightening and smoothing of the brake signal.

The device works as follows.

In normal mode (the device is in a static state) on

figure 2) the secondary current of the high-voltage current transformer has a distorted curve shape. In this case, the voltage curve at the output of the first rectifier55 l 2 is also significantly distorted. It contains mainly a constant component, the first and second harmonics, as well as a small third harmonic at the input of the matching and corrective link 1, a very small unbalance current flows, so the signals at the outputs of the first rectifier 2, filter 5 of the highest frequencies, the second rectifier 6 and smoothing scheme 7 are also small. The signal at the output of the braking signal generation unit 4 can reach a considerable value, however, the comparator 8 does not work, because the signal at its input has a negative polarity. The signal on the codes of the return time 9 element, the time delay element 10 and the output element 11 is also equal to 0.. With a sinusoidal short-circuit current in the protection zone at the input of the matching and correction link 1 k, it is also sinusoidal, therefore, the output of rectifier 2 produces a voltage that contains mainly a constant component and a second harmonic, whose amplitude relative to the constant component is about 67%. I The module of the transmission coefficient of the filter 5 is the highest frequencies for a given Q of the filter at the third harmonic frequency, 78 at the second harmonic frequency. The constant component of the filter output does not pass. The transfer coefficient of the smoothing circuit 7 is taken to be about 0.5. Taking into account the signal, the output of the smoothing circuit 7 is about 25% of the constant component of the working circuit and the output of the comparator 8 appears pulses, the pause between which is significantly less than the delay time for the return of element 9, equal to 5 ms, and its output appears a constant signal equal to 1. After setting the time delay element 10, equal to about 22 ms, a signal equal to 1 appears at its output, and the output organ 11 is triggered. At a short-circuit current with an aperiodic component in the zone action protection (see

(.porka 30% of the constant term).

The first harmonic practically does not pass to the output of the filter of the 5 highest frequencies, since the transmission coefficient of the filter at the frequency of the first harmonic is equal to 12.

Due to the third harmonic, the voltage at the output of the filter 5 of the higher frequencies, and accordingly the smoothing of the circuit 7, is greater than in the case of a sinusoidal current at the input of the protection device and is approximately 50% of the constant term. In this case, the pause time at the output of the comparator 8 is less than 5 ms, and at the output of the time delay element 9 for the return a solid signal appears. After 22 ms, a signal 1 appears at the output of the time delay element 10 and the output element 11 is triggered. With a periodic surge current magnetization (see Fig. 3) the duration of pauses in the current is less than 5 ms.

The voltage at the outlet of the first rectifier 2 during the period has three impulses, due to which the ratio is. The amplitude of the third harmonic to the constant term is quite large and is about 80%. The magnitude of the transmission coefficient of the 5th frequency filter at the third harmonic frequency, as indicated above, is assumed to be 3. In this case, the signal at the output of the smoothing circuit 7 is 0,, 5 1.2 from the constant component voltage at the output of the first rectifier 2,

which ensures the formation of pauses and the output of the comparator 8 with a duration of from -7 to 10-10 ms. In this case, a pause also occurs at the output of the return time element 9 and a time delay element 10 does not work. Accordingly, the output body 11 does not work either.

Claims (1)

Invention Formula A device for differential protection of a transformer, containing an operating circuit consisting of a matching and a correction link, connected in series with the first rectifier and a resistor, a brake signal generating unit, the output of which, together with the output of the operating circuit, is connected to the input of the comparator, the output of which is connected to serially connected a return item, an extract item for processing and an exit body, about 25 topics. what. In order to improve speed and simplify, an additional braking circuit is added to it, consisting of a series-connected high-pass filter of the second rectifier and a smoothing circuit, the higher-frequency filter input connected to the output of the first rectifier, and the output of the smoothing circuit to the comparator input, the high-pass filter has the highest gain modulus at the third harmonic frequency. ne