RU2826446C1 - Non-reversible control circuit of self-braking induction motor with displacing squirrel-cage rotor - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and can be used to drive an electric drive with a self-braking induction motor with a displacing rotor. Non-reversible control circuit of a self-braking induction motor with a displacing squirrel-cage rotor comprises a non-reversible magnetic starter consisting of a contactor with its coil and three built-in thermal protection relays, a double-pole contactor with its coil, automatic circuit breaker, fuses, a control circuit consisting of a control button connected in series with the contactor coil, a time relay with a time delay for the operation of the double-pole contactor. Ends of motor windings have common point to which neutral wire is connected.

EFFECT: improvement of operational characteristics, namely reduction of starting currents of stator winding, increase of intensity of starts, operational reliability and service life of electric motors.

1 cl, 1 dwg

Description

The invention relates to the field of electrical engineering and can be used to operate an electric drive with a self-braking asynchronous electric motor with a shifting rotor.

A control circuit for an asynchronous motor with a squirrel-cage rotor using a non-reversible magnetic starter is known (Moskalenko V.V. - Electric Drive: Textbook for students of higher educational institutions. - M.: Publishing Center "Academy", 2007. - 368 pages, pp. 196-197). The control circuit contains a magnetic starter consisting of a contactor KM and three thermal protection relays KK built into it. The circuit provides direct starting of the electric motor (without limiting the current and torque), disconnecting it from the network, as well as protection against short circuits (fuses FA ) and overloads (thermal relays KK ).

The main advantages of this control scheme are its simplicity, reliability and ease of operation.

However, the use of this control circuit for an electric drive with a self-braking asynchronous electric motor with a shifting squirrel-cage rotor has its own characteristics that manifest themselves during the process of its start-up.

The peculiarity of the process of starting a self-braking asynchronous electric motor with a shifting rotor is described in detail in the source on page 31 (Ryazentsev N. P., Shvets S. A. Self-braking asynchronous motor with a conical rotor. - Novosibirsk: "Science", 1974. - 70 p.). It indicates that after applying voltage, the rotor will begin to rotate only at the moment when

, (1)

Where - engine starting torque;

- moment of resistance of the entire unit;

- braking torque.

Braking torque ‚ created by the brake spring, is removed by axial electromagnetic force . However, the axial electromagnetic force proportional to the magnetizing current , and since they increase from zero exponentially, then for some time, while does not increase to a certain value, the rotor stands still in a braked state (short-circuit mode of an asynchronous electric motor), which leads to a sharp increase in the current flowing through the stator winding. In this case, the full value of the voltage on the stator windings creates a torque on the rotor shaft (with a braked rotor), which leads to an additional increase in the starting current of the electric motor and its intense heating at this moment.

The disadvantage of this control scheme is that its use does not reduce the intense heating of the stator winding at the moment of starting (when it is still braked) and leads to a sharp decrease in the intensity of starts of self-braking asynchronous electric motors, and with intensive operation - to an increased acceleration of the aging processes of the insulation. All this leads to premature failure of the stator winding insulation and a decrease in the operational reliability and service life of electric motors.

In addition to this, there is an increase in the starting current of electric motors, which leads to an undesirable increase in the response (disconnection) value of protective equipment installations.

As a result, this control scheme worsens the performance characteristics of electric drives with self-braking asynchronous electric motors with shifting squirrel-cage rotors.

The closest in technical essence and achieved result to the claimed invention is a non-reversible control circuit for a self-braking asynchronous electric motor with a shifting squirrel-cage rotor (RU 2796580 dated 05/25/2023, Bulletin No. 15).

The start of the electric motor M, with the automatic switch QF turned on, is carried out by pressing the button SB1 in the control circuit, while the coil of the contactor KM1 is supplied with power by connecting the voltage to one winding of the electric motor M.

The disadvantage of this control circuit is that at this point in time the current cannot flow through the winding, since the two-pole contactor KM2 is in the open state, thereby breaking the current circulation path through the other two phases. At this point in time, the absence of current flowing through the stator windings does not allow creating a sufficient axial electromagnetic force to compress the brake spring and release the rotor from the braking device and does not allow moving away from the mode during start-up, in which the rotor is in a braked state, with the full value of the voltage connected to the stator windings.

This leads to an increase in the current flowing through the stator windings, the multiplicity of the starting current of the electric motor and the intensity of heating of the stator winding at this moment, which will lead to a sharp decrease in the intensity of starting electric motors, and with intensive operation - to an increase in the aging processes of the insulation, a decrease in the service life of the stator winding insulation, operational reliability and durability of the electric motors.

The objective of the invention is to improve a non-reversible control circuit for a self-braking asynchronous electric motor with a shifting squirrel-cage rotor.

The technical result consists in improving the operational characteristics, namely, reducing the starting currents of the stator winding, increasing the intensity of starts, operational reliability and durability of electric motors.

The technical result is achieved in that the non-reversible control circuit of a self-braking asynchronous electric motor with a shifting squirrel-cage rotor contains a non-reversible magnetic starter consisting of a contactor with its coil and three thermal protection relays built into it, a two-pole contactor with its coil, an automatic switch, fuses, a control circuit consisting of a control button, united in series with the contactor coil, a time relay with a delay in the response time of a two-pole contactor, at the same time The ends of the electric motor windings have a common point to which the neutral wire is connected.

Since the ends of the electric motor windings have a common point to which the neutral wire is connected, then when phase voltage is connected to this winding of the electric motor, a current will flow through the neutral wire, which will create a sufficient axial electromagnetic force to compress the brake spring and release the rotor from the brake device.

Simultaneous connection with a time delay of the second and third stator windings of an asynchronous self-braking electric motor, due to the presence and operation of a time relay with subsequent connection of a two-pole contactor, allows to leave during start-up the mode in which the rotor is in a braked state, with the full value of the voltage connected to the stator windings. This will reduce the current flowing through the stator windings, reduce the starting current multiplicity of the electric motor and reduce the intensity of heating of the stator winding at this moment, which will lead to a sharp increase in the intensity of electric motor starts, and with intensive operation - to a decrease in the aging processes of the insulation, an increase in the service life of the stator winding insulation, operational reliability and durability of the electric motors.

As a result, the proposed control scheme improves the performance characteristics of electric drives with self-braking asynchronous electric motors with shifting squirrel-cage rotors.

The essence of the invention is explained by drawings.

Fig. 1 shows a non-reversible control circuit for a self-braking asynchronous electric motor with a shifting squirrel-cage rotor.

The non-reversible control circuit of a self-braking asynchronous electric motor with a shifting squirrel-cage rotor contains a non-reversible magnetic starter consisting of a contactor KM1 with a coil, three thermal protection relays KK built into it (Fig. 1). The automatic switch QF is used to connect the electric motor M to a three-phase voltage source (A, B, C). The ends of the windings of the electric motor M have a common point to which the neutral wire (N) is connected.

Fuses FA protect the electric motor M from short circuits in the stator circuit.

The electric motor M is started by button SB1 in the control circuit.

Button SB2 is used to brake the electric motor M.

The time relay KT is installed in series with the coil of the contactor KM1 and connects the two-pole contactor KM2 in the stator circuit with a time delay.

Thermal relay KK provides protection of electric motor M from overloads.

The control circuit operates as follows.

The electric motor M is started, with the automatic switch QF switched on, by pressing the SB1 button in the control circuit, whereby the coil of the contactor KM1 is energized by connecting the voltage to one winding of the electric motor M and the subsequent flow of current through it via the neutral wire N. The current flowing through the stator winding creates a magnetic flux that intersects the magnetic circuit of the stator and rotor. Due to the tendency of the magnetic circuit of the rotor of the electric motor M to be located in the "magnetic middle" in relation to the stator, an axial electromagnetic force arises, which compresses the brake spring. The rotor begins to move in the axial direction, thereby being released from the braking device.

At this point in time, the time relay KT is triggered (with a delay in response time relative to the start of the start) with the closing of the two-pole contactor KM2, which simultaneously connects the second and third stator windings of the electric motor M. Three-phase voltage (A, B, C) is supplied to the stator windings of the electric motor M, a torque is generated, which sets it in motion.

To switch off the electric motor M, the SB2 button is pressed. In this case, the contactor KM loses power and disconnects the electric motor M from the network. The braking process begins, during which the rotor starts moving in the axial direction under the influence of the brake spring and interacts with the braking device, followed by a stop.

To protect the electric drive from overloads during operation, the circuit includes a thermal relay KK.

Fuses FA protect the electric motor M from short circuits in the stator circuit.

Claims (1)

A non-reversible control circuit for a self-braking asynchronous electric motor with a shifting rotor, comprising a non-reversible magnetic starter consisting of a contactor with its coil and three thermal protection relays built into it, a two-pole contactor with its coil, an automatic switch, fuses, a control circuit consisting of a control button connected in series with the contactor coil, a time relay with a delay in the response time of the two-pole contactor, characterized in that the ends of the windings of the electric motor have a common point to which a neutral wire is connected.