SU843087A1 - Device for thermal protection of electric motor - Google Patents

Description

one

The invention relates to electric drives and may be used, in particular, to protect the electric motor of a hermetic compressor of a refrigeration unit.

A device for thermal protection of an electric motor is known, made on posistors connected to the input of an amplifying element made on transistors, the output of which acts on a switching device that turns off the electric motor from the TI mains.

 The closest to the proposed technical essence and the achieved effect is a device for built-in thermal protection of asynchronous motors, where posistors are placed in the most heated parts of the windings and, in case of overheating of the engine in various emergency conditions, are given; signal to the input circuit. In this case, the circuit operates by unlocking the transistor switch in the coil circuit of the relay and at its output a command appears to shut off the motor by blurring the contact of the aforementioned G2 relay.

However, due to the specific digital drive of the refrigeration unit compressor. the protection must have a self return and an increased range between the response temperature and the return temperature.

The purpose of the invention is to increase the range between the response and return temperatures.

This goal is achieved by the fact that a device for thermal protection of an electric motor, containing a stabilized DC source connected to the motor phases, the output of which includes a transistor switch with an actuator in the collector circuit and a posistor installed in the electric motor and connected to the input of the transistor switch, is additionally equipped the second transistor key, which is connected by its input to the second posistor installed on the electric motor, and the output to the common executable Yelnia body, wherein the emitter of the second transistor switch circuit is connected to the negative terminal of the power source through the normally open contact actuator .organa.

The drawing shows a device for thermal protection of an electric motor.

The device contains a power source 1, transistor switches 2 and 3, relay 4, pin 5, motor b, positor 7, pin 8, posistor 9,

The device works in the following way.

In the cold state of the engine fcpaHSHCTOpHHe, the keys 2 and 3 are locked, | the coil of the relay 4 is de-energized and its current. contact 5 in the engine control circuit b allows the latter to operate.

When, in emergency mode, the temperature of the motor winding rises to a certain value, the resistance of posistor 7 increases and key 2 is unlocked. Power is supplied to relay coil 4, which opens its own NC. Pin 5 on engine control circuit b turns it off. Simultaneously closes the io. contact 8 of the relay and creates a parallel power supply circuit of the relay coil, since the key 3 also qTKpiJT from increasing the engine temperature and changing the resistance of the posistor 9.

When the motor is turned off, the key 2 locks in accordance with the characteristics of the posistor 7 and the setting. But the coil of the relay 4 continues to be supplied through a parallel circuit with the key 3. The key 3 is locked and, therefore, de-energizes the coil of the relay 4 and turns on the engine only when it is cooled to the specified temperature, which is controlled by the switch 9.

In refrigeration units, self-return protection is required and this is provided by the proposed device when the engine is cooled to a predetermined temperature.

Claims (2)

Invention Formula A device for thermal protection of an electric motor containing a stabilized DC source connected to the phases of the electric motor, the output of which includes a transistor switch with an actuator in the collector circuit and a posistor 5 connected to the input of the transistor switch, characterized in that in order to increase the range between temperature operation and return, it is equipped with a second transistor switch, which, with its input, is connected to the second position of the transistor mounted on the motor, and the output - to a common actuator, while the emitter circuit of the second transistor switch is connected to the minus pin of the power source through the closing contact of the actuator. Sources of information taken into account in the examination 1, USSR Author's Certificate 357644, cl. H 02 M 7/08, 1978. 2. USSR author's certificate number 432631, cl. H 02 H 7/08, 1974.