SU982137A1 - Device for protection of three-phase electric motor - Google Patents

Description

(5) DEVICE FOR ZA111IT1 1 THREE-PHASE ELECTRIC MOTOR

one

The invention relates to electrical engineering and can be used to protect three-phase electric motors from failure during emergency operation.

A device for protecting a three-phase electric motor is known, comprising two current transformers, a negative sequence filter, and an electronic amplifier circuit. This, c device protects the motor from phase failure and overload 1.

However, this device does not provide reliable motor protection, 5 liters. In addition, it is unstable in the real asymmetry of electrical networks

Closest to the proposed technical entity is a device for protection of a three-phase electric motor containing a starter, a transformer unit connected to a phase-sensitive detector, a shunt thyristor connected to protection relay C23

The said device also does not provide reliable protection of electric motors in conditions of high humidity because it does not allow monitoring the insulation state of the motor windings.

The purpose of the invention is to increase the reliability of motor protection.

Claims (2)

The goal is achieved by the fact that a device containing a starter, a transformer unit, a phase-sensitive detector and a shunt thyristor connected to a protection relay is provided with a threshold device and an ICh logic element whose first input is connected to the output of the specified threshold device, the second input is connected to the output of the phase-sensitive detector and its output is to the control electrode of the shunt thyristor, and the starter winding is connected to the 3982 phase of the motor power supply via the closing contact of the protection relay you. The drawing shows a schematic diagram of ycTpoftcYea to protect the electric motor. In the proposed device, a transformer block 2 is connected to the supply phases A, B, C of the motor 1, the outputs of which are connected to the inputs of the phase-sensitive detector 3, and the output of the detector 3 is connected to one of the inputs of the OR element k, the second input of which is connected to the output of the threshold device 5. The output of the OR element is connected to the control electrode of the thyristor 6 connected in parallel to the protection relay 7. The rectifying unit 8 is connected to the protection relay 7 through a limiting resistor 9. The coil of the actuator 10 is connected to the phase B of the power supply via the closing contact 11 of the protection relay 7. The power phases A, B, C are connected to the inputs of the transformer block 2 through the power contacts 12 of the starter 10. In addition, one of the inputs of the block of transformers 2 is connected to the power phase C via the threshold device 5 and the control buttons 13 and 14. Parallel to the button 14 is included the closing contact 15 of the actuator 10. The device operates as follows. When the start button 14 is pressed, power is supplied to the threshold device 5. rectifier unit and protection relay 7. In the event that the insulation of the windings is moistened, the leakage current through the threshold device 5 and the moistened insulation material of the winding to earth is greatly increased. In this case, the threshold device 5 is triggered, the signal lamp is lit, the output signal of the threshold device 5 through the logic element OR 4 turns on the thyristor 6, which bypasses the turnips 7 of protection. The speed of the electronic part of the circuit is more than an order of magnitude higher than the speed at which the electromagnetic protection relay 7 is turned on, which ensures a clear shunting of the relay coil and the impossibility of switching on the electric motor. In this way, the electric motor is protected from failure during insulation breakdown. To restore the normal insulation properties of the windings, the motor must be dried. If the insulation state of the windings is normal, the threshold device 5 does not generate a signal, after supplying power from the rectifying unit 8 to the protection relay 7, it triggers and, with its contact 11, switches on the starter 10, which, in turn, turns on the electric motor 12 1, and pin 15 bypasses the start button 14. In the event of other emergency modes - phase failure or overloads, a signal appears at the output of the phase-sensitive detector 3, which through the logic element OR 4 is fed to the control electrode of the thyristor 6. The thyristor is turned on, the protection relay 7 is shunted and its contact 11 turns off the starter 10, which, in turn, switches off the motor 1 through the contacts 12. The device is especially effective when operating in conditions of high humidity or with long interruptions in operation. Claims. A three-phase electric motor protection device containing a starter, a transformer unit connected to a phase-sensitive detector and a shunt thyristor connected to a protection relay, characterized in that, in order to increase the reliability of protection, it is equipped with a threshold device and a logic element OR, the first input of which connected to the output of the threshold device, the second input is connected to the output of the phase-sensitive detector, and its output is connected to the control input of the shunt thyristor, while the winding of the actuator is connected Chen phase power to the motor through a relay closing contact. Sources of information taken into account in the examination 1. USSR author's certificate number 741365, CL, H 02 And 7/08, 1980. 2. USSR author's certificate number 771794, cl. H 02 H 7/08, 1980, O A B C O O O  H - / 4