SU1705944A1 - Device to protect a three-phase motor against asymmetric modes - Google Patents

Abstract

The invention relates to electrical engineering and can be used to protect a three-phase electric motor from asymmetrical modes and, as a result, overheat its windings. The aim of the invention is to increase the sensitivity of protection by ensuring control of the mutual influence of the asymmetrical mode and the motor load on the heating of its windings. When the phase is broken, as well as with voltage unbalance and at a certain load of the electric motor, a voltage appears at the output of the negative sequence filter 10, which through the diode bridge 11 and the voltage divider 12 is applied to the load resistor 13, the currents flowing through the thermistors 16 - 1.8 and the load resistor 13, the input of the adder 19 is supplied, the base current of the transistor And increases, which triggers the relay 5, its contact 9 opens, de-energizes the coil 2 of the magnetic starter, and the motor stops. 1 il. r to

Description

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J17059 The invention relates to electrical engineering and can be used to protect a three-phase electric motor from asymmetrical modes and, consequently, overheat its windings;

The aim of the invention is to increase the sensitivity of protection by taking into account the mutual influence of the asymmetrical mode and the load of the electric motor on the heating of its windings.

The drawing shows the electrical circuit of the proposed device.

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A device for protection of a three-phase electric motor 1 contains a magnetic starter with a coil 2, the power contacts 3 of which are connected to the phase conductors of the network, and others to the terminals of the motor through the thermal relays k, and relay 5 tension The coil 2 of the magnetic starter is connected to the terminal with a terminal for connection to the mains phase conductor, and the second terminal via the Start button 6 and the Stop 7 button connected in series with the terminal for connecting another phase network cable. The Start button 6 is bridged by a chain consisting of from the series-connected blocking contact 8 of the magnetic actuator and the disconnecting contact 9 of the voltage relay 5. The device also contains a reverse sequence filter 10 connected by its inputs to the terminals for connection to the phase terminals of the electric motor 1. The outputs of the filter 10 are connected to the inputs of the rectifying bridge 11, the positive terminal of which is connected to the first terminal of the voltage divider 12, and the negative terminal to the second the output of the voltage divider 12 and the negative output of the power source (not shown). The middle point of the voltage divider 12 is connected to the first output of the load resistor 13. The device also includes an executive unit in the form of a transistor k, the emitter of which is connected to the negative terminal; the power source, the base with the output of the adjusting resistor 15, and the collector through the coil of the voltage relay 5 with the positive output of the power source. The load sensor is made in the form of three thermistors 16, 17 and 18, connected by their first outputs

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Dami with a positive output power source. The second inputs of the thermistor 16, 17 and 18 and the load resistor 13 are connected to the first input of the adder 19. The second input of the adder 19 is connected via a compensating resistor 20 to the negative terminal of the power source. A second output of a control resistor 15 and a first output of a feedback resistor 21 are connected to the output of the adder 19, the second output of which is connected to the first input of the adder.

A device for protection of a three-phase electric motor from asymmetrical modes works as follows. In the symmetric mode with a permissible load, the voltage at the output of the filter 10 is absent. The currents flowing through the thermoresistors 16-18 are fed to the input of the adder 19. The base current of the transistor k is small, the voltage relay 5 does not operate, its contact 9 in the control circuit of the magnetic starter is closed and the motor 1 is working normally. In the symmetric mode, when the motor is overloaded due to the additional heating of the thermal relay plates, the resistance value of the thermistors 16-18 decreases, which causes an increase in the total current input to the input of the sum- Torus 19. This increases the base current of the transistor 1, the voltage relay 5 operates, contact 9 is opened, de-energizing the coil 2 of the magnetic starter, and the motor 1 is stopped. With a break (as well as with voltage imbalance) and with a certain load of the electric motor, a voltage appears at the output of the filter 10 of the reverse sequence. The voltage rectified by a diode bridge 11 is supplied through a voltage divider 12 to the load resistor 13. The currents flowing through the thermistors 16-18 50 and the load resistor 13 are fed to the input of the adder 19. The base current of the transistor 1 increases, which leads to operation relay 5, its contact 9 opens, de-energizes the coil 2 of the magnetic starter, and the electric motor 1 stops. The voltage divider 12 regulates the level of response by reverse voltage, and

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by the lyric resistor 15 is the trigger level for the loading of the electric motor, gate. Resistor 20 compensates for the effect of the environment on the operation of the adder 19.

The device can be used transistor KT815, as well as the chip KYOUD7.

The use of the proposed device to protect the motor from asymmetrical modes provides an increase in the service life of engine insulation, reduced repair costs and replacement of machines, and also eliminates simple process equipment.

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Claims (1)

Apparatus of the Invention A device for protection of a three-phase electric motor against asymmetrical modes, comprising a magnetic starter, the power contacts of which are connected to the terminals of the network by 25 terminals and 25 to the terminals of the electric motor via thermal relays, voltage relays, the power source, the coil of the magnetic starter, the first output, is connected to the terminal for connection to the phase conductor of the network, and the second output is connected via the Start button and in series with it th Stop button - a terminal for connection to another phase conductor of the network, the Start button shunted chain consisting of the series-connected auxiliary contact actuator and magnetic tripping relay contact voltage feedback filter posledo35 40 , ) 5 10 20 25, 05EM sequence, connected by its inputs to the terminals for connection to the phase terminals of the electric motor, to the outputs of the above-mentioned filter podkly4 prices inputs of the rectifying bridge, the plus output of which is connected to the first output of the voltage divider, and the negative output to the second output of the voltage divider and negative output power supply, the middle point of the voltage divider is connected to the first output of the load resistor, the executive body in the form of a transistor, the emitter of which is connected to the negative output of the power source, - with a regulating resistor output, a collector through a voltage relay coil - with a positive power supply output, characterized in that, in order to increase the protection sensitivity by taking into account the mutual influence of the asymmetrical mode and the motor load on the heating of its windings, it is additionally equipped with an adder, compensating a resistor, a load sensor in the form of three thermistors connected by its first leads to a positive output of the power source, while the second you are connected to the first input of the adder water thermistors and load resistor, the second input of the adder through a compensating resistor is connected to the minus terminal of the power source, the second output of the adjusting resistor and the first output of the feedback resistor are connected to the output of the adder, the second output of which is connected to the first adder input. 35 40