RU10801U1 - MOTOR THERMAL PROTECTION DEVICE - Google Patents

Abstract

A device for thermal protection of an electric motor, comprising a thermal relay and an electric motor connected to a single-phase network source through normally connected normally closed contacts of the thermal relay, its winding and a common power wire, characterized in that the working winding of the thermal relay is connected in series only with the working winding of the pump motor, excluding its inclusion in the general power supply circuit of the electric motor.

Description

ШШ F04D 15/00

MOTOR THERMAL PROTECTION DEVICE

The proposed solution relates to the field of electrical engineering and can be used, for example, to protect against overloading of domestic submersible centrifugal pumps equipped with single-phase condenser squirrel-cage motors.

A device for thermal protection of an electric motor is known, comprising a power source, a temperature sensor mounted on the windings of the electric motor and connected to the input of the control unit, the output of which is connected to the actuator thyristor 1.

However, this device does not have sufficient accuracy and reliability of operation.

The closest technical solution to the proposed is a device for the protection of single-phase squirrel-cage motors. .., made on the basis of a thermal relay, where the protected motor is connected to a single-phase network through a normally-closed PTT type thermal relay contact, a thermal relay winding, and a common electric motor power supply wire connected in series. The relay is configured in such a way that, if a mechanical short circuit occurs, or if the current exceeds a permissible current, the on time and pause duration provide a steady-state thermal mode of the electric motor that does not exceed the temperature-permissible windings. The thermal relay is configured according to the failure current to the current consumed by the electric motor in the nominal C 2 mode.

However, this wired circuit has a low response speed, which worsens the protective functions of the circuit against inrush currents exceeding its rated value, and can lead to an overstatement of the stator winding overheating and failure of the pump motor. As shown by the practice of using this circuit in an electric pump such as a VCP manufactured by our enterprise, the electric pump is switched off after 40-45 seconds, which leads to heating of the stator winding to a temperature close to critical.

Thus, the goal of creating the proposed technical solution is to increase the response time of the circuit of the pump motor circuit from short circuit currents with a simultaneous increase in its reliability.

The essence of the proposed technical solution is to change the inclusion of the working winding of the thermal relay in the circuit only of the working winding of the pump motor, instead of including it in the general power supply circuit of the motor, which allows you to get the current multiplicity in the winding of the thermal relay in / more than in the motor winding, and thereby halve the response time of the protection (i.e., the response time will be 15-20 seconds). Since the multiplicity of the current is determined by the ratio of the current consumed by the electric motor in emergency mode to the current setting of the relay and, given that the currents in the nominal mode are located at an angle with each other, it can be assumed that

- 2 a, the fo and V & e currents in the nominal mode are close in magnitude, and they can be conditionally phase as Oi and the mechanical short-circuit current as

Yez k.ro.% Evil

/ without

 e ;,

/ W t.l-

 - the current consumed from the network during mechanical short circuit of the rotor of the electric motor;

 - current flowing through the working winding of the electric motor during mechanical short circuit;

h current flowing through the auxiliary winding of the electric motor during mechanical short circuit; X ,, is the reactance of the capacitor.

Given that X is significantly greater than e, the short circuit current of the auxiliary winding C) is much smaller than j

Comparative analysis with the prototype shows that the claimed device is distinguished by the presence of a new connection formed by the inclusion of a working winding, a thermal relay in series only with the working winding of the pump motor without branching the current into two circuits, which allows to obtain a current multiplicity of 1L2 more than the total the motor power supply circuit and thereby reduce the response time of the input by half (i.e. 15-20 sec for PTT or PTJO relays.

f.

". Where

COMMUNICATION exhibits a new property, expressed in reducing the response time of the pump motor protection circuit. This allows us to conclude that the technical solution meets the criterion of significant differences.

In FIG. 1 shows a diagram of a device where a thermal relay of the RTL type is used, a capacitor C 20 uF of type K42-19, PO is the working winding of the electric motor, OB is the auxiliary winding of the electric motor.

The device for thermal protection of the electric motor was manufactured in the Energia research and production concern (association), in the Source LLP of the city of Voronezh.

The device uses a single-phase short-circuited

750 W electric motor, where V is thus 5 l / Ofe- e. In our case

Y ((r - - /, 9

Thus it is seen that in nominal mode

,. / g and:. With maximum rotor short circuit

 - V U .o

Based on the foregoing, we conclude that the multiplicity of the current of the mechanical short circuit of the rotor in the BITS working winding is higher than the multiplicity of the current consumed from the network by the electric motor, which reduces the response time by half.

The device operates as follows.

When voltage is applied to the input terminals of the thermal relay, current through normally closed contacts and the relay coil will flow to the electric motor. The pump is in operation. When the rotor is jammed, the current strength 2 is higher in the working winding of the electric motor and the bimetallic relay contacts due to this open quickly tra -10 ft

pee 2 times than in the prototype. The power circuit and electric motor are de-energized after 15-20 seconds.

Experimental studies of the inventive device for thermal protection of an electric motor as a part of a single-phase capacitor short-circuited electric motor and thermal relay showed that, in comparison with a device of a similar purpose (prototype), the inventive device provides a twofold increase in the response speed of the pump motor protection circuit and increases its reliability.

Claims (1)

A device for thermal protection of an electric motor, comprising a thermal relay and an electric motor connected to a single-phase network source through normally connected normally closed contacts of the thermal relay, its winding and a common power wire, characterized in that the working coil of the thermal relay is connected in series only with the working winding of the pump motor, excluding its inclusion in the general power supply circuit of the electric motor.