SU1598019A1 - Device for differential protection of electric units - Google Patents

Abstract

The invention relates to electrical engineering and can be used as a differential current protection for electrical installations. The purpose of the invention is to increase the sensitivity of protection by reducing the unbalance current. This goal is achieved by the fact that the protection is performed according to the principle of voltage equilibrium, and the power of the reacting organ is supplied by the differential current transformed into a voltage. 1 il.

Description

The invention relates to electric power industry and is intended for the implementation of relay protection for busbars, power transformers and reactors.

The purpose of the invention is to increase the speed and sensitivity by reducing the unbalance current.

FIG. 1 shows a diagram of a device for two connections; in fig. 2 - curves of currents and voltages.

The device contains current transformers 1 connected at the ends of the connections 2 of the protected object 3, intermediate transformers 4-7, two of which 5 and 6 are loaded on resistors, the rest on a chain of dual zener diodes 8, two circuits 9 and 10 of voltage doubling, the first which is connected through the threshold element 11 with the reacting authority 12.

Curves of currents and voltages explain the operation of the device in the mode of internal (Fig. 2a) and external (Fig. 26) damage (Arabic indices correspond to the numbers of elements in the diagram (Fig. 1), (- contact state of the reacting organ, zero signal corresponds to the open state of the contact).

The voltage to open the Zener diodes 8 is selected from the condition

.2i ,,

where Ufo is the response voltage of the response organ.

The tripping setting of the protection is regulated by resistors in the secondary circuits of the transformers 5, and 6 and the tripping voltage of the threshold element 11.

A voltage equal to the sum of the positive and negative polarity voltages is applied to the input of the threshold element 11, which must be taken into account when selecting the trigger voltage of the threshold element.

By adjusting the resistors in the secondary circuits of transformers 5 and 6, the voltage at the input of the voltage doubling circuit is equal to zero in normal mode.

The device works as follows.

In case of internal damage, all connection currents are directed to the protected

SP

WITH

oo

with

to the object. The voltage at the input of the voltage doubling circuit 9 is proportional to the sum of the connection currents. The signal at the output of voltage doubling circuit 9 is proportional to the sum of the connection currents after passing the positive and negative polarities. This voltage exceeds the pickup threshold of the threshold element and conditions for protection operation are created. The output voltage of circuit 10 doubled after passing two opposite polarities of current becomes 2 (/ 8st) which leads to triggering of threshold element 11 and reacting organ 12. Thus, the response time of protection is around the period of industrial frequency (total operating time of threshold element and reacting authority 2–3 ms).

In case of external damage to saturation of one of the magnetic circuits of the current transformers of the connections, the sum of the voltages on the secondary windings of the intermediate transformers 5 and 6 and, consequently, the voltage at the input and output of the doubling circuit 9 is zero. After the current transformer magnet is saturated at time 8, a voltage of 1 / 5.6 appears. This voltage may exceed the pickup voltage of threshold element 11. But the voltage at the input of doubling circuit 10 is unipolar (like unbalance current), therefore, the output of this circuit is f / 8cT. which is not enough for a reactive body to work.

Claims (1)

Invention Formula A device for differential protection of electrical installations containing current sensors. 0 intended to be installed at the ends of the protected object, a series-connected threshold element and a reacting organ whose output is an output of the device, characterized in that, in order to increase speed and sensitivity by reducing the unbalance current, four intermediate transformers are introduced, two variable resistors , a dual Zener diode and two voltage doubling units, with the primary windings of the first and second intermediate transformers connected in series and connecting The primary windings of the third and fourth intermediate transformers are connected in series and connected to the output of the second current sensor, the unipolar terminals of the secondary windings of the first and third intermediate transformers are combined and connected to the dual zener diodes, which also connected to the first and second inputs of the first voltage doubling unit, the outputs of which are connected to the power terminals of the threshold element, to the secondary windings of the second and fourth intermediate x transformers are connected to the first and second variable resistors, respectively, the first different-pole outputs of the secondary windings of the second and fourth intermediate transformers are connected, the second opposite-pole outputs of the secondary windings of the second and fourth intermediate transformers are connected to the first and second inputs of the second voltage multiplier, outputs which are connected to the first and second inputs of the threshold element, respectively. ag. / iJ a five hl U.L u. w a po  Paa.Z