SU1410162A1 - Apparatus for providing redundancy for failures of switches and protection devices - Google Patents

Abstract

The invention relates to relay protection of electrical systems and power supply systems and can be used to back up failures of switches and protections connected to common voltages of 6-10 kV connections with step-down transformers. The purpose of the invention is to increase the sensitivity to single-phase short-circuits of downstream connection transformers. In the self-starting mode, the currents are symmetrical, and at the inputs of the instantaneous measuring elements 16 and 17 there is a voltage with a small variable component. When the measuring elements 16 and 17 are triggered, continuous signals appear at their outputs, and the prohibiting input of the BANGE 20 element from the measuring element 17 is given a signal that blocks the device’s action. With single-phase short-circuits behind the transformers, the phase currents are asymmetrical and the voltage at the inputs of the measuring elements 16 and 17 has a large variable component. At small instantaneous values of the input voltage, the measuring element 17 returns, removing the signal from the prohibiting input of the BANGE 20 element and allowing the measuring element 16 through pulse expanders 18 and 19, the OR 21 logic element to act on the delay unit 22, which through the executive unit 23 acts on shutdown bus systems. In case of interphase damages, the measuring unit 14 is triggered, acting through the logic element OR 21 and the delay unit 22 on the execution unit 23. 1 h. item f-ly, 2 ill. i (Л С

Description

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The invention relates to relay protection of elements of electric systems and power supply systems and can be used to back up failures of switches and protection of connections connected to common buses with a voltage of 6-10 kV with step-down transformers.

The aim of the invention is to increase the sensitivity to single-phase short circuits.

FIG. 1 is a diagram of the electrical network and the structural scheme of the proposed device; in fig. 2 - vector and time diagrams for device operation.

The electrical network consists of a busbar section 1, to which connections 2, 3 with step-down transformers are connected, current transformer 4, 5 is installed in two phases of each connection.

The device for backing up failures of switches and protectors contains current converters 6–9 to the voltage of two phases of each connection, rectifying bridges 10–13, the inputs of each of which are connected to the outputs of the corresponding converters 6–9, and the outputs of all rectifying bridges 10–13 merged. The various output terminals of the current transducers in the voltages of the two phases of each connection are combined (when the number of power connections differs from the two, the number of current transducers into voltage and the number of rectifying bridges change accordingly).

The combined outputs of the rectifying bridges 10–13 are connected to the input of the measuring unit 14. The asymmetry detection unit 15 contains the first 16 and second 17 measuring elements, the first 18 and second 19 pulse extenders, and the logical element 20 BAN. The inputs of the first 16 and second 17 measuring elements of the unit 15 are connected in parallel to the input of the measuring unit 14. The output of the first measuring element 16 is connected to the input of the first expander 18 of pulses, the output of which is connected to the control input of the BANNER element 20. The output of the second measuring element 17 is connected to the prohibitory input of the BANNER element 20, the output of which is connected to the input of the second expander 19 of pulses. The output of the second expander 19 of pulses is connected to one of the inputs of the OR 21 logic element. The output of the measuring unit 14 is connected to the second input of the OR 21, the output of which through the delay block 22 is connected to the input of the execution unit 23 acting as a trip tire systems.

The device works as follows.

Combining the multi-polar output terminals of the current transducers into the voltage of the two phases of the connections allows realizing

Establish a three-phase rectifier circuit in the presence of two-phase voltage sources and two rectifier bridges.

When the outputs of all rectifying bridges 10–13 are combined, a max-selector circuit is formed and the inputs of the measuring unit 14 and measuring elements 16 and 17 of the asymmetry detection unit 15 are fed at each time point to the maximum of the voltages at the outputs of the converters 6–9.

The measuring unit 14 and the measuring elements 16 and 17 are configured and configured as follows.

The response voltage of the measuring unit 14 (Ucpu) is selected from the condition of ensuring the failure in the self-starting mode of the load. If the input voltage exceeds the response voltage of the measuring unit 14, then a continuous signal appears at its output.

0 The first 16 and second 17 measuring elements of the asymmetry detection unit 15 are carried out inertialess.

The tripping voltage of the first measuring element 16 (Ucpie) is selected from the condition of providing the required sensitivity to single-phase short circuits and down-conversion transformers.

The response voltage of the second measuring element 17 (Ucpir) is selected from the failure condition in normal operation.

In the self-starting mode, the load currents of the connections form a three-phase symmetric system (Fig. 2a), obtained using the three-phase rectifier circuit, the voltage at the input of the measuring unit 14 and the measuring elements 16 and 17 has a small variable component. In this mode, the measuring unit 14 does not work, and the measuring elements 16 and 17 may operate. Moreover, since the variable component of the input voltage is small, in the case of the operation of the measuring elements 16 and 17, continuous signals appear at their outputs. The presence of a continuous signal at the inhibit input of the element 20 BAN

The c does not allow the device to trip.

In a single-phase short circuit, a step-down transformer with a winding connection circuit / K has a short-circuit current on the high-voltage side in

0 the damaged phase will be twice the current in the intact phases and opposite to them in phase (Fig. 26). In this case, the voltage ivx14.1b, 17 has a large variable component. In this case, the measuring unit 14 does not work, and the measuring elements 16 and 17 at certain times trigger. When the first measuring element 16 triggers, the discontinuous signal at its output is converted into a continuous pulse 18 by the first expander 18 and fed to the control input of the BAN element 20. The second measuring element 17 during the time when the instantaneous value of the input voltage is less than its response voltage returns, so at these times the signal is not sent to the inhibitory input of the element 20 BAN, the signal arrives at the input of the second expander 19 pulses. The intermittent signal from the output of the BANGE element 20 is converted into a continuous pulse 19 by a second pulse expander and is transmitted to the delay element 22 via an OR 21 gate. If after a specified time the signal does not disappear, which indicates a failure of the switch or the protection of the damaged connection, the device acts to shut down the system of women.

In case of a phase-to-phase short circuit, the measuring unit 14 is triggered at one of the connections, and in case of failure of the switch or the main protection of the damaged connection, the time delay device acts to switch off the women.

In order to provide a better build-up from the influence of load currents with single-phase short circuits behind step-down transformers, it is possible to use several asymmetry detection units with measuring elements with different response voltages.

Thus, if there are connections on the sections with step-down transformers, the proposed device is triggered by single-phase short-circuits behind the transformers by reacting not only to the value of the connection currents, but also to the value of asymmetry

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phase currents, which provides a higher sensitivity to these damages.

Claims (2)

Claims. A device for backing up failures of switches and protections containing, at each connection, two phase-to-voltage converters, the output of which is connected to the corresponding rectifying bridge, the outputs of all the rectifying bridges are combined and connected to the input of the measuring unit, the delay unit whose output is connected to the input an actuator unit, characterized in that, in order to increase the sensitivity to single-phase short circuits, additionally, an OR input is introduced, the first input of which is connected to the output of the measuring unit, and the output - to the input of the delay unit, an asymmetry detection unit connected by two inputs to the common outputs of rectifying bridges, the output of the unbalance detection unit is connected to the second input of the OR logic gate, the opposite-polar output terminals of the current-to-voltage converters for each connection are combined. 2. A device according to claim 1, characterized in that the asymmetry detection unit comprises a first measuring element, the input of which is the first input of the asymmetry detection unit, its output is connected to the input of the first pulse expander, the output of which is connected to the first input of the BANNER element, the second measuring element, the input of which is the second input of the asymmetry detection unit, is connected via its output to the second input of the BAN element, the output of which is connected to the input of the second pulse expander, the output of which is the output of the unbalance detection unit. 1s iwh W.fB.r /