SU788253A1 - Device for testing serviceability of protection circuits of three-phase type - Google Patents

Description

one

The invention relates to electrical engineering and can be used to monitor the health of relay protection devices.

A device for monitoring the health of protection circuits in a three-phase design is known, which contains a current relay included in the return wire of the secondary circuits of current transformers 1.

A disadvantage of the known device is that it does not provide monitoring of the operability of the sensing units of the measuring protection relays.

The closest technical solution to the invention is a three-phase protection circuit health monitoring device comprising a zero sequence filter and a reacting element 2 connected to its output.

However, this device controls the health of voltage circuits only and does not control the health of current circuits and sensing blocks of measuring protection relays.

In a number of protections, for example, remote ones, it is advisable to monitor both voltage circuits and current circuits.

The purpose of the invention is to increase the reliability of protection by monitoring the operability of sensing units of measuring protection relays and the possibility of monitoring current circuits.

This goal is achieved by what in

A device for monitoring the health of protection circuits in a three-phase version, made in the form of three identical sets of measuring relays, containing a filter

10 zero-sequence, the output of which is connected to the reacting element, additionally introduced three adders with the number of inputs for each equal to the number of outputs of the sensing units of one set of relays, the negative sequence filter, the second responding element and the two-input logic element OR. the first, second and third inputs of the mmators are connected to the outputs of the sensing units of the first, second and third sets of the relay, respectively, the same inputs of the reverse and zero sequence filters are pairwise connected to each other and connected to the outputs of the adders, the second response element is connected to the output of the negative sequence filter , and the outputs of the reacting elements are connected to the inputs of the logic element OR, the output of which serves as the output of the device. In addition, to prevent a false alarm signaling a protection failure during an unbalanced short circuit in the primary network, a time element is additionally inserted in the device, the input of which is connected to the output of the OR element, and its output serves as the output of the device. The drawing shows a block diagram of the device in relation to monitoring the health of the distance protection circuits. The circuit contains a protected line 1 with a switch 2 and current transformers 3, a voltage transformer 4, resistance measuring relays 5-7, each of which consists of sensing units 8 and 9 and comparison unit 10, protection logic unit 11 and health monitoring device 12 protection circuits containing adders 13-15, a zero sequence filter 16, an inverse sequence filter 17, reacting elements 18 and 19, a logical element OR 20, and a time element 21. Relays 5-7 resistance, which are the measuring bodies of one of the protection stages, are the same and have equal settings. The control device works as follows. In the normal symmetric mode of operation of the protected line 1 and when the transformers 3 and 4 of the current and voltage and their secondary circuits are in good condition, the currents and voltages supplied to the relay 5-7 of resistance are symmetrical and form direct sequence systems. Since the relays 5-7 of the resistance are the same, and their settings are equal, the values of the signals at the outputs of the like sensing units of these relays are associated with the values of the currents and voltages connected to them with the same linear ratios. Therefore, the signals at the outputs of like sensing units 8 (9) are symmetrical. Consequently, the signals at the outputs of the adders 13-15 are also symmetric, and the values of the signals at the outputs of the filters 16 and 17 of the inverse and zero sequences are equal to 0. The responding elements 18 and 19 are in the inoperative state B, and there is no signal at the output of the control device 12. When installed in the secondary circuits of current transformers 3, for example, the breakage of one of the phase conductors, the symmetry of the currents connected to the relay is violated. Consequently, the symmetry of the signals at the outputs of the like sensing units 8 and 9 and the signals at the outputs of the adders is violated. Moreover, since the relay 5-7 resistance is connected to the difference of the phase currents, the asymmetry of the signals at the outputs of the sensing power currents 8 (9) and the adders 13-15 is caused only by the components of the reverse sequence, and the zero-sequence components are not. The value of the signal at the output of the reverse sequence filter 17 becomes different from zero, the reacting element 19 is triggered and through the element OR 20 and the element 21 of time gives a fault signal. Similarly, the control device works even if the secondary circuits of the transformer 4 are damaged. If the protection circuit itself is damaged, for example, the sensing unit 8 of the resistance relay 5, the symmetry of the signals at the outputs of the sensing blocks 8 and, consequently, the signals at the outputs of the adders 13-15 is violated. Since the damage to the sensing unit 8 of one of the resistance relays 5, the symmetry of the impedance violated violates the signal value at the output of only the damaged sensing unit 8 and does not affect the signal values of the same intact sensing blocks 8 of the other relays 6 and 7, the asymmetry is caused by the inverse and zero components sequences. The values of the signals at the outputs of the filters 16 and 17 of the zero and inverse sequences become different from zero. Responsive elements 18 and 19 are triggered and through the element OR 20 and the element 21 of time gives a fault signal. In practice, the exact equality of the zero values of the signals at the outputs of the filters 16 and 17 of the zero and inverse sequences in the normal mode of operation of the protected line 1 and the absence of damage in the protection circuit is usually not achieved. Due to the unbalance of the primary currents and voltages, the faults of their transformation by transformers 3 and 4 of the current and voltage, errors in signal generation by the sensing blocks 8 and 9, the unbalance signals that are different from zero are constantly present at the outputs of filters 16 and 17 of the zero and inverse sequences. To eliminate the false triggering of reactive elements, their thresholds must exceed the values of the corresponding unbalance signals. In this case, a symptom of a malfunction is not just the appearance of values of signals other than zero at the outputs of the filters of the inverse or zero sequence, but values exceeding the response thresholds of the reacting elements. When the measuring relays 5-7 are switched on for the difference of phase values, the value of the unbalance signal at the output of the zero sequence filter 16 does not depend on the asymmetry of the currents and voltages applied to the measurement relay, but is determined only by the error signals generated by the sensing units 9. Therefore, the response threshold of the response element 18, the zero sequence filter included at the output 16 will be less than the response threshold of the response element 19. Therefore, the response element 18 that does not respond when stated failures of current transformers and voltage and secondary circuits, provides bolschoy sensitivity than responsive member 19 to damage the sensing unit measuring relay. The reacting element 19 is activated when both the current transformers 3 and the voltage 4 and their secondary circuits, and the receiving units 8 and 9 of the measuring relays 5-7 are damaged.

The response of the reacting organs 18 and 19 occurs not only in the case of damage to the protection circuit, but also in violation of the symmetry of the primary quantities, as a result of short circuits. The prevention of a false alarm of protection failure is provided by a time element 21 having a time delay exceeding the short circuit duration. When using a control device without a time element 21, a triggering element is required that is triggered in case of a short circuit and which blocks the signal from the control device.

Claims (2)

1. A device for monitoring the serviceability of protection circuits in a three-phase version, made in the form of three identical sets of measuring relays, containing a zero-sequence filter, to the output of which a reactive element is connected, characterized in that, in order to increase the reliability of protection by performing monitoring: operability of sensing units; .1 measuring relays and the possibility of making counter current circuits, three adders were added to it with the number of inputs each, 0 equal to the number of outputs of sensing units of one relay set, negative sequence filter, second reacting element and two-input logic element OR, with inputs of the first, second and third adders connected to the outputs of sensing units of the first, second and third sets of relays, reverse filter inputs of the same name and zero sequences are pairwise connected to each other and connected to 0 outputs of adders, the output of the filter of the reverse sequence is connected to the input of the second reacting element, and the outputs of the reacting elements are connected to the inputs of the logic element OR, the output of which serves as the output of the device. S 2. The device according to claim 1, characterized in that, in order to prevent a spurious signal of protection failure during an asymmetrical short circuit in the primary network, it is additionally introduced into it 0 time element whose input is connected to the output of the OR element, and its output serves as the output of the device. Sources of information taken into account in the examination 1. Kazansky V. Ye. Relein protection. ML, Gosenergoizdat, 1960, p. 165. rice, 97. 2, Fedoseev A, M, Releina protection of electrical systems. M., “Energie, 1976, p. 284 fig. 4-59.