SU1410166A1 - Apparatus for differential protection with delay - Google Patents

Abstract

This invention relates to electrical engineering, namely, to relay protection. The aim of the invention is to increase the sensitivity of differential protections. This goal is achieved by the addition of a key 15 to the differential protection braking circuit, the position of which determines the braking mode. The position of the key 15 is controlled by a form control unit 16. The relative magnitude of the higher harmonics — the ratio of the absolute level of the higher harmonics to the differential signal — determines the location of a short circuit in or outside the protected zone and, depending on it, the key 15 is injected with sufficient braking for reliable operation or inadequate protection. 1 il.

Description

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The invention relates to electrical engineering, namely, relay protection, can be used to protect the tires of electrical installations, generators, transformers and other electrical equipment.

The aim of the invention is to increase the sensitivity.

FIG. 1 shows a block diagram of a device for differential protection with braking; in fig. 2 - dependence of the relative level of higher harmonics on the total error of the CT at external and internal short-circuit.

The device contains current sensors, made in the form of current transformers (CTs) 1, 2, 3, the secondary windings of which are connected to the inputs of current-voltage converters 4-6, to the outputs of which a differential signal conditioner (FDS) 7, consisting of connected adder 8 and driver module 9 module drivers 10-12 brake circuit modules, the outputs of which are connected to the driver 13 of the brake signal (FCS), made in the form of an adder. The output of the FCS 13 is also connected to the output of the inverter 14, whose input is connected via key 15 to the output of the FDS 7. The output 16 of the differential signal shape control (BF.F) consisting of series-connected high-pass filter 17 is connected to the output of the 18 the high-frequency module of the sum of connection currents, dividing unit 19 and threshold element 20, the second input of dividing unit 19 connected to the output of the FDS 7. The output of threshold element 20 is connected to the control input of the key 15. The output of the FTS 13 is connected to the brake input of the reactive Gana (RO) 21. At working RO input 21 is supplied with the output signal of FDR 7, proportional to the differential current. The division unit 19 may be performed, for example, by the log of atoms. All module drivers are made with anti-aliasing.

The device works as follows.

The currents of the shoulders, taken from the secondary windings of the CT 1 -3 of the same phase, are transformed into a voltage proportional to them using 4-6 current-to-voltage converters. By the adder 8, the instantaneous values of the signals are summed. The amount rectified by the module 9, proportional to the differential current, is fed to the working input of the reacting body 21 and acts in the direction of operation. The signal from the output of the adder 8 is also fed to the input of the block 16 controlling the shape of the differential signal. Here, using a high-pass filter 17, a signal is selected that is proportional to the level of higher harmonics and arrives at the first input of the block.

ka 19 division through shaper 18 module. A differential signal from the output of the differential signal generator 7 is supplied to the second input of the division unit 19. The signal at the output of division unit 19 is proportional to the ratio of higher harmonics to the differential signal and fed to the input of threshold element 20. The output signal of threshold element 20 appears when the input signal (relative level of higher harmonics) exceeds a given level, which is with short circuit outside the protected area. The signals from the outputs of the converters 4-6, the current through the formers 10-12 of the brake circuit module are fed to the inputs of the FCS 13. The input of the FCS 13 through the switch 15 also supplies a differential signal inverted by the inverter 14 from the output of the PDS 7, proportional to the geometric sum of the arm currents. Thus, the output of the FCS

0 13 a vehicle is formed, proportional to the arithmetic sum or the difference of the arithmetic and geometric sum of shoulder currents (depending on the position of the key 15), and is fed to the brake input of the reacting or5 channel 21.

As a signal controlling the position of the key 15, the relative level of higher harmonics (OVG) is used - the ratio of the absolute level of the higher harmonics to the differential signal. The dependencies of the TGM on the total TT error with the internal (line 22) and external (line 23) short-circuit are presented in FIG. 2 for the initial period of occurrence of a short-circuit at a constant primary circuit time of 0.05 s. View of these

5 dependencies are quite stable, does not depend on the ratio of short-circuit current. If we take a certain level of OUVG beyond the threshold level (dotted line in Fig. 2), it becomes possible to identify the location of a short circuit (inside or outside the protected area) with an accuracy sufficient to control the braking. With internal short circuit braking is undesirable. TC, proportional to the difference between the arithmetic and geometric sums of shoulder currents, dramatically reduces braking when internal and provides build-up when external short circuits are not accompanied by a deep saturation of the TT. This corresponds to the area below the selected threshold level of the AHU. With external faults, accompanied by large ITT errors (area above the threshold level), it is advisable to switch to a vehicle proportional to the arithmetic sum of shoulder currents, ensuring protection in this mode, since it is possible to set the maximum deceleration rate. This embodiment of the device for differential protection with braking allows

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significantly increase the sensitivity of protection, in which, depending on the degree of saturation of the CT and the location of the short circuit, automatically (due to the operation of the control unit of the differential signal form 16 and the key 15), the selection of the appropriate vehicle supplied to the reacting authority 21 occurs.

Claims (1)

Invention Formula A device for differential protection with braking, containing current sensors with leads for connection to the primary connection circuit of the protected object, the secondary windings of which are connected via a current-to-voltage converter to the inputs of the adder and to the inputs of the drivers of the brake modulus, the outputs of which are connected to the inputs of the brake driver whose output is connected to the first input react0 organ, the adder's output is connected to the input of the high-pass filter and to the input of the generator of the operating signal module, the output of which is connected to the second input of the reacting authority, the output of the high-pass filter is connected to the input of the high-frequency module forming unit, the sum of the connection currents In order to increase sensitivity, a dividing unit, a threshold element, a key, an inverter are additionally introduced, the first input of the dividing unit is connected to the output of the high frequency module forming unit The second input is connected to the output of the forming unit of the working signal module, and the output through the threshold element is connected to the control input of the key, the output of the forming unit of the working signal module is through the key element and the inverter is connected to the input of the braking signal generator. 10 20 30 itO 50 60 70 80 FIG. 2 f%)