SU1053215A2 - Differential bus-protection relay - Google Patents

Abstract

RELAY DIFFERENTIAL TIRE PROTECTION by author. St. No. 625283, characterized in that, in order to increase selectivity during external short circuits using protective current transformers with a gap in the magnetic core, a pulse width limiter is additionally inserted between the output of the main square wave former and the Inhibit element.

Description

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The invention relates to electrical engineering, and specifically to relay protection of electrical systems, and can be used to protect tires and linings.

According to the main author. St. No. 625283 known: but a relay of differential protection of women, containing a working circuit consisting of: current transformers and a rectifying bridge, a brake circuit consisting of two current transformers, rectifying washing and a smoothing circuit, two formers of rectangular pulses, the first of which - the main one, is connected to the difference between the working and brake circuits, and the second one is supplementary, connected to the brake circuit, and the output of the first square-wave former is connected via series-connected low-pass filter, the left time element and the OR element to the executive body, and the output of the second rectangular pulse generator via the second time element is connected to the inhibit input of the Ban element, the signal input of which is connected to the output of the first rectangular pulse generator, and the output through the return element is connected to the second one input element OR 1.

A disadvantage of the known relay is the possibility of over-tripping in case of external short-circuits in the presence of a significant aperiodic component in the current unbalance of the differential circuit of the secondary windings of protective current transformers. This may be the case for protective current transformers with a gap in the magnetic core, since their error is normalized only by the periodic component.

The purpose of the invention is to increase the selectivity of the relay when external short circuits are used when using protective current transformers with a gap in the magnetic circuit.

This goal is achieved by the fact that a pulse width limiter is added to the differential protection relay of women, which is connected between the output of the main square wave former and the inputs of the low-pass filter and the Node element.

. FIG. 1 shows the scheme of the proposed relay; in fig. 2 - voltage at the outputs of the corresponding relay units with external {fig. 2 a) and internal short circuits x (Fig. 26), as well as the voltage at the output of the working and brake circuits.

The relay contains a current transformer 1, the primary winding of which is included in the differential secondary circuit of protective current transformers (not shown), and the primary windings of current transformers 2 and 3 are connected to protective current transformers installed in the arms of the protected object. The secondary winding of the current transformer 1 is connected to a rectifying bridge 4, the output of which forms an operating circuit, and the secondary windings of current transformers 2 and 3 are connected to rectifying bridges 5 and 6, the outputs of which form a brake circuit connected to a smoothing circuit containing a resistor 7- 10, a diode 11 and a capacitor 12.

The first driver of 13 rectangular pulses connected to the difference between the working and brake circuits through a pulse width limiter 14 connected in series, a low-pass filter 15, the first time delay element 16 and the OR element 17 are connected to the actuator 18. The second driver 19 of rectangular pulses, connected to the output of the brake circuit, connected through the second element 20 of the time delay to the inhibit input of the element of the Inhibit 21, the signal input of which is connected to the output of the limiter 14 of the pulse duration ow, and the output through the element 22 time delay for return is connected to another input of the element OR 17.

The proposed relay works as follows.

In the normal load mode, a small unbalance current flows through the primary winding of current transformer 1, so the output of the first generator 13, duration limiter 14, low-pass filter 15 and first time delay element 16 is equal to 0. Current flows through primary windings of transformers 2 and 3 protection shoulders, so on the resistor 7 and. capacitor 12 has a rectified voltage. However, it is not sufficient to trigger the former 19. Diode I prevents the discharge of capacitor 12 through a resistor 7. Resistor 9 is used to regulate the deceleration rate of the relay.

The signals at the outputs of the second element 20 of the time delay, the logical element of the Prohibition 21, the element 22 of the time delay for the return and the logical element OR 17 are equal to 0. Executive body 18 is not triggered.

In the event of a short circuit outside the protected zone, the transient unbalance current (Fig. 2a) contains aperiodic and periodic components. When using protective current transformers with a gap in. the magnetic circuit is an aperiodic component in the current unbalance more periodic. As a consequence, at the output of the imaging unit 13, a rectangular pulse with a duration of several duration of the industrial frequency occurs (it continues until Up UT). On output, the limiter is 14 pulse widths of the order of 7-10 ms, which causes a transient in the low-pass filter 15. The low-pass filter 15 has a resonant frequency close to the network frequency, therefore the duration of the positive half-waves does not exceed 15 ms, and element 16, which has a time delay of 20-25 ms. does not work. The signal at the output of the first shaper 13 appears later than the signal at the output of the second shaper 19, therefore the signal at the output of the element No suppression occurs. Executive body 18 does not work. At short circuit in the protected zone, a rectified sinusoidal current arises at the input of the former 13, which is used as an impedance current 1/1 MJlCntlDlrl nnj Jri t tfiuii.iM.xt1 vi. (Fig. 2 b). In this case, rectangular pulses with a frequency of 100 Hz appear at the output of the former 13. These pulses pass through a limiter 14 with a duration of almost no change. At the output of the low-pass filter 15, a voltage appears that contains a constant component and a second harmonic of an insignificant value. In this case, the voltage curve does not intersect the time axis and the time delay element 16 is triggered. Since the signal at the output of the first shaper 13 appears earlier than the signal at the output of the second shaper 19, the element Prohibition 21 has time to trigger and ensure the passage of the tripping signal to the second input of the OR element 17. Thus, the relay is activated by two channels. The invention can find a wide with 1 ---, -1l D-protection of wrinkles and faults both in conjunction with protective current transformers with gaps in the magnet duct, and in conjunction with protective current transformers without a gap in the magnetic drive.

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Claims (1)

RELAY OF DIFFERENTIAL TIRE PROTECTION by ed. St. No. 625283. characterized in that, in order to increase the selectivity for external short circuits when using protective current transformers with a gap in the magnetic circuit, an additional pulse duration limiter is inserted, which is included between the output of the main square-wave driver and the inputs of the low-pass filter and the Prohibition element. !