RU1791895C - Device for protection of a c electric motor against short-circuit - Google Patents

Abstract

Usage: relay protection of electric motors against short circuits, Summary of the invention: the device comprises a reference voltage sensor 1, signal level regulators 2-5 with limiters, comparators 6-9, adder 10, key circuits 11-14 on D-flip-flops, executive block 15, operation indicators 16-19, analog OR circuit 20 and current-dependent time delay circuit 21. When a short circuit occurs the comparator 5 is activated and LOG.1 appears at its output, which goes to the input of the adder 10 and the first input of the key circuit 12. From the output of the adder LOG.1 goes to the second input of the circuit 12. When the signals match, the key circuit 12 is overturned and fixes the operation protection. From the direct output of the 12 LOG circuit. 1 is fed to the input of block 15, the output of which is LOG. Oh, the power contactor turns off. 1 ill.

Description

The invention relates to the field of electrical engineering, and more particularly to relay protection and can be used to protect electric motors from short circuits,

The purpose of the invention is to increase the speed and reliability of the device with any kind of short circuit.

The drawing shows a functional diagram of the device presented by the device, which consists of a sensor-1 reference voltage, regulators 2, 3, 4, 5 of the signal level with limiters, comparators 6, 7, 8, 9, adder 10, key circuits 11 , 12, 13,14 on D-flip-flops, of the executive unit 15, made according to type 4 OR-NOT, indicators 16, 17, 18, 19 of operation, analog circuit 3 OR 20 and circuit 21 of the current-dependent time delay, performed on the timer KR 1006 VI1. The outputs of the current measuring transducers (not shown in the drawing) are connected to the inputs of the regulators 2,3,4 and the inputs of the circuit 20, the output of which is connected to the input of the controller 5 and circuit 21. The output of the controller 5 is connected to the first input of the comparator 9, the second input of which is connected to the output of the sensor 1, and the output - to the input of the circuit 21 and the second input of the circuit 14, the first input of which is connected to the output of the circuit 21, the inverse output - to the input of the circuit 19, and the direct output - with the input of block 15. The outputs of the regulators 2,3, 4 are connected to the second inputs of the comparators 6, 7, 8, the first inputs of which x are connected to the sensor 1, and the outputs are connected to the outputs H, K, L (for communication with a computer), the first inputs of the key circuits 11, 12, 13 and the inputs of the adder 10, the output of which is connected to the second inputs of the circuits 11, 12, 13 the direct outputs of which are connected to the input of block 15, and the inverse outputs are connected to the inputs of indicators 16, W, 18.

A short circuit can be with an electrically strong contact and with an arc discharge. The first is characterized by a sharp inrush current, many times higher than the rated current. In an arc discharge, the current rise may not exceed 2-3 JHOM. Starting currents when turning on the motors can reach 2-7 JHOM depending on the starting conditions. The duration of the start-up cycle is determined by the engine power and shaft load.

The protection device operates as follows. From the sensor 1, a reference signal is supplied to the first inputs of the comparators 6, 7, 8, 9, the value of which is regulated within 1/3 Un-Un (Un is the supply voltage of the protection device). By changing the value of the reference signal, the deadband threshold between the rated current of the controlled network and the trip current of the protection and the level of noise protection are regulated.

The second inputs of comparators 6, 7, 8 receive signals from current converters through regulators 2, 3, 4 with limiters. The magnitude of the signal can be adjusted from zero to maximum. By changing the value of the useful signal, the proportionality factor K J (j aKT / JHOM is set by the level controller. The signal level limiter is designed to protect the input of the comparator from overload.

If the rated current flows in the network, signals of such a magnitude that the comparators are not triggered from the outputs of the converters. On their outputs log.O. Accordingly, at the inputs and outputs of the adder 10 and the inputs of the circuits 11, 12, 13 log.O. At the direct outputs of the key circuits and inputs of block 15 is also a log. The power contactor is on.

From the outputs of the converters, the signals also come through the circuit 20 and the controller 5 to the input of the comparator 9 and, in addition, from the output of the circuit 20 to the circuit 21, which is shunted to the housing in the initial position. Then, at the inputs of the key circuit 14, the O. log and, therefore, at the direct output is also the log O, which goes to the input of block 15. The device is in standby state.

If a short circuit occurs with an arc discharge in one or several phases, both to the housing and between the phases (for example, phase A), the current consumption in the phase will increase. As a result of this, the signal at the output of the phase A converter will be such that, going through circuit 20 and regulator 5, it will trigger the comparator 9, which is set to К if actual / other 2 (if actual current in phase, JHOM - rated current in phase). The comparator can be set to any K.

Simultaneously with the output of circuit 20, the resulting signal is fed to circuit 21 of the delay of operation of the protection. From the output of the comparator 9, log.1 goes to start the circuit 21 and simultaneously to the first input of the circuit 14. If the network status has not been restored during the delay time and the short circuit continues, then the log will go from the output of the circuit 21 to the second input of the circuit 14. 1. The key circuit breaks over and locks in the protection. From the direct output of the circuit 14 log. 1 enters the input of block 15, at the output of which a log appears. О and the power contactor breaks the load circuit.

From the inverse output of the circuit 14, the log.O causes the indicator 19 to turn on.

If during the delay the network state has recovered, i.e. the short circuit stopped, then from the first input of the circuit 14 log. 1 is removed and the log came to the second input. 1, after a time delay, the rollback of the key circuit will not cause and the device will remain in standby state. The response delay time is determined by the start cycle and is set for each particular engine.

When a short circuit occurs with an electrically strong contact (for example, in phase B), the current in the network increases sharply K JC KT / JHOM 7. A comparator 7 is triggered, which can be set to any value of K, and log.1 appears at its output, which goes to the input of the adder 10 and the first input of the circuit 12, From the output of the adder log.1 goes to the second input of the circuit 12. When the signals match, the key circuit overturns and fixes the protection. From the direct output of the circuit 12 log. 1 enters the input of block 15. At its output, a log O appears, which turns off the power contactor. From the inverted output, the log O turns on the operation indicator 17. Since the signal transit time is measured in nanoseconds, the inertia of the power contactor will be the main source of the delay of operation,

Claims (1)

The claims A device for protecting an AC motor from a short circuit, comprising a current converter, a comparator, a time delay element with an inverse current-dependent response characteristic, and an executive unit, characterized in that, in order to increase the speed and reliability of operation for various types of short circuit, it is equipped with an analog OR element, phase-by-phase comparators, three phase and fourth signal level controllers, three phase and fourth key elements, an adder and a reference voltage sensor, while the current measuring transducer is made phase, each in the stroke is connected to the input of the phase regulator of the signal level and the input of an analog OR element, the output of which is connected to the input of the time delay element with an inverse current response characteristic and the input of the fourth regulator of the signal level, the output of which is connected to the input of the comparator, the second input of which is connected to the output of the reference voltage sensor, the output of the comparator is connected to the input of the time delay element and the first input of the fourth key element, the second input of which is connected to the output of the exposure element time, and the direct output of the fourth key element is connected to the input of the executive unit, while the output of the phase regulator of the signal level is connected to the input of the phase comparator, the output of which is connected to the input of the adder and the first input of the phase key element, the second input of which is connected to the output of the adder, and the direct output of the phase key element is connected to the input of the executive unit. 0 5 0 5 0 5