SU1394320A1 - Device for protecting three-phase electric motor against emergency condition - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection. The purpose of the invention is to increase the reliability and sensitivity of the device. The device contains fast-current transformers 1-3, rectifiers 4 and 5, a voltage presence unit (BNN) 6, a pulse sequence control unit 7, an integrating unit 8, a threshold amplifier (PU) 9 and an actuator (IO) 10 with resistors 12 - 14, diodes 15 - 17 and a transistor 18. When a two-phase mode occurs at: the output of the rectifiers 4 and 5, the constant component voltage decreases and the variable changes with a frequency of 100 Hz. Transistor 18 periodically closes and opens. The high level pulses arising at the output of the BNN 6 are fed to the integrating unit 8 and the PU 9 turns on the EUT 10. The electric motor is disconnected from the network. 1 hp f-ly, 1 ill. yu (L

Description

00

from 4 to to

The invention relates to electrical engineering, in particular to devices for protecting electric motors from emergency operation.

The purpose of the invention - povypie reliability and sensitivity of the protection device.

The drawing shows a circuit diagram of a device for protection.

The device consists of fast-absorbing transformers 1 - 3 current, three-phase half-wave rectifiers 4 and 5, block 6 voltage presence in NIN, block 7 control of the sequence of current pulses in transformers 1-3, integrating block 8, threshold amplifier-block 9, The transistor 23 remains closed for the presence of a constant voltage on its gate, which is provided by elements 20 - 22. High-level pulses arising at the output of block 6, flow unhindered to the integrating block 8. When reaching the output of the block and 8, a voltage sufficient to trigger the threshold amplifier unit 9, the actuator 10 is turned on and the motor is disconnected from the network.

When a decelerated rotor mode occurs, the primary currents in transformers 1 - 3 to 4 - 7 | times increase. The current transformers 1-3 are saturated, the constant component of the rectified voltage supplied

35

Complementary body 10, block 11 pi-2o from blocks A and 5, is reduced to zero, tannin. At the same time, the current pulse sequence control unit 6 has resistors 12-14, diodes 15-17, transistor 18. The voltage presence unit 7 consists of resistors 19 and 20, 25 of capacitor 21, diode 22, field-effect transistor 23. The integration unit 8 has a variable resistor 24.

The device works as follows.

From the moment of supplying the voltage to the device and the absence of current in the primary windings of transformers 1–3 current (electric motor not started) transistor 18 of pulse sequence control unit 6 is closed, since there is no signal at the output of rectifier 4. The field effect transistor 23 of the control unit 7 for the presence of current is open, since the voltage across the gate is n 0. The output of the current pulse train control unit 6 is shunted and the signal to the input of the integrating unit is not received.

If there is current in the primary windings of transformers 1 to 3 current (the motor operates in full phase mode), the output voltage of the rectifiers 4 and 5 is sufficient to open the transistor 18 and close the transistor 23. The device is in control mode.

When a two-phase operation occurs at the output of the rectifiers 4 and 5, the constant component of the voltage decreases to zero, and the variable component changes with a frequency of 100 Hz. The transistor 18 periodically closes and opens, and the field

and the variable component is changing at a frequency of 150 Hz, and the device operates like a two-phase mode of operation.

When the motor starts at the first moment, the device operates similarly to the mode of the braked rotor. The detuning from the starting period is made by the resistor 24 of the integrating 30 block 8. The latter simultaneously protects the device from false triggering with impulse noise.

The execution of a block of current pulse sequence on a transistor, three diodes and three resistors, the introduction of a current presence block in current transformers on a field-effect transistor and a threshold amplifying block allows you to refuse the reed relay in the current pulse sequence control unit and use low-power current transformers.

The invention improves the efficiency of the device for protection in connection with an increase in their reliability and sensitivity.

45

50

55

Claims (2)

1. Device for protection of three-phase asynchronous electric motor from emergency mode, containing, by the number of phases, fast-spreading current transformers, the secondary windings of which are connected in a star and connected to the inputs of the first and second three-phase half-wave rectifiers switched on oppositely, the power supply unit. from blocks A and 5, decreasing to zero, and the variable component is changing at a frequency of 150 Hz, and the device operates like a two-phase mode of operation. When the motor starts at the first moment, the device operates similarly to the mode of the braked rotor. The detuning from the starting period is made by the resistor 24 of the integrating unit 8. The latter simultaneously protects the device from false triggering with impulse noise. The execution of a block of current pulse sequence on a transistor, three diodes and three resistors, the introduction of a current presence block in current transformers on a field-effect transistor and a threshold amplifying block allows you to refuse the reed relay in the current pulse sequence control unit and use low-power current transformers. The invention improves the efficiency of the device for protection in connection with an increase in their reliability and sensitivity. Invention Formula 1. Device for protection of three-phase asynchronous electric motor from emergency mode, containing, by the number of phases, fast-spreading current transformers, the secondary windings of which are connected in a star and connected to the inputs of the first and second three-phase half-wave rectifiers switched on oppositely, the power supply unit. The output of the first rectifier is connected to the actuator through a series-connected pulse sequence control unit, an integrating unit and a threshold amplifying unit, characterized in that, with an overall increase in reliability and sensitivity, it is equipped with a control unit for the presence of current in the power supply network, the input of which is connected to the output of the second three-phase single-wave rectifier, the output to the output control of the pulse sequence, which is made on a transistor, three diodes, three resistors, while the first resistor is connected to the input of the specified block, the second resistor connected in series and three diodes in the forward direction are connected in parallel with it, parallel to the second and third diodes The base-emitter transition of the transistor is turned on, the third resistor is connected to the collector circuit of the transistor, the other end of the resistor is connected to the power supply unit, the collector connection point of the transistor and the third resistor is the output terminal of the unit (the sequence of the pulses. 2. The device according to claim 1, characterized in that the control unit for the presence of current is made on two resistors, a diode, a capacitor and a field-effect transistor, the first resistor connected to the input of the unit, a second resistor and a capacitor connected in parallel to it the gate-to-source transition of the field-effect transistor is connected in parallel to the capacitor, parallel to the second resistor the diode is connected by an anode to the gate of the field-effect transistor, the drain of which is the output terminal 25 control unit availability of current.