SU1621114A2 - Differential protection device - Google Patents

Abstract

This invention relates to electrical engineering, in particular, to relay protection of electrical installations. The purpose of the invention is to increase the selectivity of work with external short circuits. The goal is achieved by the fact that an additional differential channel is inserted in the device, including a differential current transformer, rectifier, third threshold organ, and element I. 4 Il.

Description

The invention relates to electrical engineering, and can be used to protect the alternating current portions of ship electric power systems from short circuits.

The aim of the invention is to increase the selectivity of operation during external short circuits.

Figure 1 shows a block diagram of a device for differential protection; figure 2 - diagram of the differential current transformer; FIGS. 3 and 4 show timing diagrams of the operation of the functional blocks (with the designation of the output voltages at the output of the respective blocks) during a short circuit in the zone and outside the protection zone, respectively.

The device for differential protection contains primary current sensors 1, fast-current intermediate current transformers 2, blocks 3 and 4 of forming differential and brake signals, comparison element 5, two threshold elements 6 and 7, blocking body 8, BAN 9, element OR 10, output organ 11, differential current transformer 12, rectifier 13, third threshold organ 14, element 15.

As a differential transformer for current 12, a compact compensation transformer can be used: a current-voltage switch, the primary windings 16 of which consist of one coil and connected to the outputs of the primary current sensors, the winding 17 is a feedback winding and serves to compensate for the primary ampere turns, and a winding 18 - a signal winding. With the help of resistors 19 and 20, the gain of the operational amplifier 21 is set. An active low-pass filter is built on the elements 19, 22 and 21.

The output member 11 includes a tripping time element with a 5 ms delay for detuning from the unbalance pulse voltage and a pulse extender.

The device works as follows.

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In the normal mode (the device is in a static state), the sum of the currents flowing to the buses is approximately equal to the sum of the currents flowing from the buses, therefore the signals at the outputs of the differential signal generating unit 3 and the differential current transformer 12 are small. At the output of block A, the signal, depending on the load current, can reach a significant value, but the threshold organs b and 7, as well as the output organ 11, do not work, since at their input the brake signal has a negative polarity. The threshold organ 14 does not work in this mode due to the insufficient size of the input signal.

Does not work the output body 11 and in the event of a pulsed disturbance at the input of any threshold organ, since the threshold organs 6, 7 and 14 are connected according to the And 15 scheme.

In the event of a short circuit in the protection zone (Fig. 4), the outputs of the differential signal generating unit 3 and the current differential transformer 12 appear differential signals, which are large in terms of the response values of the threshold organs 6 and 14. In this mode, the additional channel is the differential transformer 12 , rectifier 13, third threshold organ 14, element I 15 - does not significantly limit the duration of the rectangular pulses of the main channel and at the output of the element 15 the pulse duration is always more than 5 ms, which is called AET actuation element 11 output.

In case of an external short circuit, the differential current is equal to the unbalance current, reaching in a transient mode at the output of the block 3 forming a differential signal of large values. Moreover, the unbalance voltage contains a constant component having the character (form) shown in Fig.4. Therefore, the duration of the rectangular pulses of the threshold blocks at the output with increasing

external short-circuit currents can be more than 5 ms, which can cause a false positive of protection. The unbalance voltage at the output of the differential current transformer 12 does not contain a constant

component. Since the primary current sensors 1 at the supply and feed connections have different sizes, the periodic unbalance voltage at the output of the differential current transformer 12 is sharply non-sinusoidal. Therefore, the duration of rectangular pulses at the output of the threshold organ 14 is noticeably shorter than the duration of the pulses at the output of the threshold blocks b and 7, and

the output element And 15 pulse duration does not exceed 2-3 ms. which is not enough to trigger the output organ tt.

Thus, the introduction of an additional differential channel allows

improve the selectivity of protection in case of external short circuits by eliminating false alarms.

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Claims (1)

Invention Formula Device for differential protection auth.St. No. 847426, characterized in that, in order to increase the selectivity of operation during external short circuits, a series-connected differential current transformer, rectifier, third threshold element and element I are additionally introduced, the primary windings of the differential current transformer are connected to the outputs of current sensors , and the output of the element IL And through the element And is connected to the output body. 77 nineteen gs 22 G. T 20 About 2 iby fig 2 A / hz A Uycm.6 Ub P D P