Non-contact shutdown of the starting winding of the electric motor. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Non-contact shutdown of the starting winding of the electric motor. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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The article describes a simple device for non-contact disconnection of the starting winding of a single-phase asynchronous motor with a squirrel-cage rotor at the end of the process of its start.

At the same time, the device provides self-starting of the engine after a power outage and engine stop.

It is possible to use a device for starting capacitor motors with automatic non-contact disconnection of the starting capacitor and ensuring their self-starting, as well as for starting three-phase electric motors in single-phase mode.

In "Electrica" 1/02, p.5, a diagram of the non-contact separation of the starting winding of a single-phase electric motor (EM) was published by using a capacitor included in the diagonal of the diode bridge for direct current. At the end of the capacitor charge, the diode bridge is “locked” by the capacitor charged to the amplitude value of the mains voltage and the current flow through the starting winding stops, i.e. the starting winding is automatically taken out of operation at the end of the process of starting the EM.

The proposed idea of turning off the starting winding of the ED is not new and has already taken place on the pages of periodicals (see Bull. Image N44, 30.11.86, RL 6/93, p.27).

The disadvantage of the proposed solution is the lack of the possibility of self-starting of the ED in the event of a power failure in the supply network and the absence of constant monitoring of the operation of the latter. As a result, the capacitor remains in a charged state, and the working winding of the EM is connected to a de-energized network through the contacts of the motor switch.

When the voltage is restored in the network, the working winding of the EM is flowed by current, and the starting current is practically absent, since the capacitor is charged, as a result, starting the EM is impossible, its working winding overheats and the engine fails. For the same reason, the device cannot be used to start a capacitor EM, since the starting torque on the EM shaft may not be sufficient for self-starting under load.

The figure shows a schematic diagram of the device, which provides more reliable operation of the EM with a non-contact separation of the starting winding with the possibility of using it for capacitor EMs. The proposed technical solution is protected by copyright [1].

Non-contact disconnection of the starting winding of the electric motor

The device contains a bipolar switch SA1 for two positions, with the help of which contacts 1-2 and 3-4 connect the working winding P of the electric motor to the network and the starting winding P connected in parallel with it through the diode bridge VD1 ... VD4 through the alternating current circuit. Diode bridge in the DC circuit it is closed by a time-setting RC circuit, which performs the functions of a dynamic phase shifter, which provides a phase shift of the current of the starting winding relative to the working one. As a result, a starting torque occurs on the EM shaft.

Switch contacts 2-5 and 4-6 provide connection of the RC-chain to the terminals of the working winding of the EM when it is disconnected from the network. Capacitor C1 makes it possible to use the device for starting and operating an electric motor with two windings constantly on during operation (capacitor electric motors).

The device works as follows. When the ED is turned on with the help of a two-pole switch SA1, its working winding P and the starting winding P are flowed through the closed contacts 1-2 and 3-4 of the switch. In this case, the positive half-wave of the current of the starting winding P passes through the diode VD1, the capacitor C of the timing RC circuit, the diode VD2, and the negative half-wave through the diode VD3, the capacitor C, the diode VD4. As a result, capacitor C provides a shift between the currents of the starting and working windings of the ED, and the latter starts.

As the capacitor C charges, the current through the starting winding decreases. After a period of time determined by the capacitance of this capacitor, the bridge diodes are locked, as a result, the current flow through the starting winding stops. ED start is over.

During the operation of the ED, the capacitor C is always in a charged state. When the ED is disconnected from the network, the capacitor C is connected through contacts 2-5 and 4-6 of the SA1 switch to the terminals of the working winding P and is discharged to this winding, while creating a braking torque on the shaft and thereby simultaneously preparing the ED for restart, i.e. . ensuring zero readiness of the latter.

The disappearance of voltage in the supply network during the operation of the EM leads to the discharge of the capacitor C on the resistor R, as a result, the circuit is automatically ready to restart the ED, which ensures its self-start when the voltage in the supply network is restored.

Details. As a switch SA1, any one suitable for current and voltage is used. Diodes VD1 ... VD4 for micromachines (up to 600 W) - diode blocks KTs402A, B ... KTs405A, B for 500, 600 V and current 1 A or four diodes of the KD202 type with letter indices M, N, R, C. Capacitor C1 is selected approximately at the rate of 7 μF per 100 W of power of the EM type MBGO-2, KBG-MN or MBGCH, which is preferable, for a voltage of at least 400 V.

Capacitor C of the timing chain - any electrolytic capacitance C \u2d (3 ... 1) C400 and voltage 450, 2 V. Resistor R of the MLT-50 type for 100 ... XNUMX kOhm.

The device during operation of the ED does not consume electricity and practically does not require adjustment.

References:

USSR author's certificate N1274100, class H02R 1/42, Appl. 01.03.84/XNUMX/XNUMX.

Author: K.V. Kolomoitsev

See other articles Section Electric motors.

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