SU1432652A1 - Device for protecting three-phase induction motor from two-phase operation and braked-rotor duty - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to devices for protecting electric motors from emergency operation. The purpose of the invention is to increase the reliability and sensitivity of protection devices. The device contains three fast-sinking current transformers, three load resistors, a three-phase single-field rectifier, a control unit for the sequence of current pulses, an integrating unit, a zener diode, an actuator and a power supply unit. New is the supply of the device with a differentiation unit and an amplifying element, the execution of a current pulse control unit based on a transistor connected in a common emitter circuit, and a differentiation unit based on a capacitor, diode and transistor, and s also supplying the device with new functional links mi Device j / can be widely used in all areas of industry and agriculture where asynchronous three-phase electric motors are used. 2 Il.

Description

The invention is from the state of electrical engineering, in particular, to devices for protecting electric motors against emergency modes of operation.

The purpose of the invention is to increase the reliability and sensitivity of the device.

Fig. 1 is a circuit diagram of a protection device; FIG. 2 shows a differential block I with a transistor optocoupler.

Device for protection consists of fast-dissolving current transformers 1-3, loaded on resistors 4-6, three-phase half-wave rectifier 7, unit 8 of control of the sequence of current pulses, block 9 of differentiation J integrating unit 10, Zener diode 11, transistor amplifier 12, an executive element 13. The current pulse train control unit includes a transistor 14, diodes 15-17, resistors 18 and 19. The differentiation unit consists of a capacitor 20, a diode 21 and a transistor 2-2, the integrating unit includes a capacitor 23 and a trimmer resistor 24. A differentiation unit 9 can be made on a capacitor 20, a diode 21, and a transistor optocoupler 25 (FIG. 2). The device also has a power supply, terminals 26 and 27.

The device works as follows.

In the normal mode of operation of the motor, the output of the rectifier 7 has a constant component of the rectified voltage. The transistor 14 of the control unit 8 of the sequence of current pulses is open, and the capacitor 20 of the differentiation unit is discharged.

When a two-phase operation occurs, the constant component of the output voltage of the detector 7 decreases to zero, the transistor 14 starts periodically with a frequency of 100 Hz, opens and closes, and the capacitor 20 periodically charges and discharges, causing periodic opening of the transistor 22 (25 In this case, the voltage pulses charge the capacitor 23. When the voltage across the capacitor 23 reaches the Zener diode 11, the amplifier on the transistor 12 and the performer

 ) 26522

np element 13 disconnects the motor from the mains

In the event of a braked rotor mode, the currents in the power wires of the motor increase by 4-7 times, from which the transformers 1-3 become saturated and the constant is k) L1; and the rectified voltage at the output

) The Q-score of goal 7 is reduced to zero. Transistor 14 periodically with a frequency of 150 Hz begins to close and open, causing a periodic charge and discharge of the capacitor 20, and consequently, periodic opening and closing of the transistor 22 (25) and further, as described, the disconnection of the motor from the network. The off delay is controlled by a resistor 24

20 and is chosen longer than the motor start-up time in order to de-energize the starting currents.

The use of a transistor opto pair allows powering

25 of the integrating unit and the executive body from another voltage level.

The implementation of block 8 of the control of the sequence of current pulses on the transistor allows to increase the sensitivity and reliability of the block, the presence of block 9 to reliably distinguish between emergency modes, and the presence of an amplifier on transistor 12 to reliably align the integrator and the actuator to provide significant exposures and increase the sensitivity of the device.

In the case of the proposed device provides more sensitive and reliable protection than the known.

Claims (1)

Invention Formula A device for protection of a three-phase 45 asynchronous electric motor against operation on two phases and a mode of a braked rotor, containing three fast-setting current transformers, the primary windings of which are intended phase wires. and the secondary ones are loaded on resistors, connected by a star and connected to a three-phase single-half-wave rectifier, a control unit for a sequence of current pulses, a differentiation unit, an integration unit, the output of which through a zener diode is connected to the amplifier input on a transistor that is loaded on a transistor The core element is connected to the control unit of the pulse power supply, characterized by the current output, which is connected to what, in order to increase the reliability, from the input of the differentiating unit, sensitivity, the output of the three-phase rectifier is connected to the input of the unit The input is connected to the input of the integrator. The input is connected to the input of the integrator. 26