SU439877A1 - Device for controlling the mode of operation of an asynchronous motor - Google Patents

Description

one,

This invention relates to the field of electrical engineering.

There are known devices for controlling the operating mode of an asynchronous electric motor, which contain current transformers connected to the first and second phases of the load and a phase relay to a shooting device connected in series with the winding of the Executive relay between the second and third phases of the network.

In order to simplify and increase the reliability in the proposed device, the secondary windings of current transformers are connected in series between the cathode and the control electrode of the thyristor.

FIG. 1 shows a diagram of the described device; FIG. 2 - waveforms of voltages.

In series with the load 1, the primary windings of the current transformers 2 and 3 are included in the first and second phases. The secondary windings of these transformers are connected in series and connected between the cathode and the control electrode of the thyristor 4. All windings are wound in one direction. A diode b is connected in series with the control electrode to rectify the control signal and increase the reliability of the thyristor. Actuator 6 (relay or blinker) is connected in series

with thyristor 4 between the second and third phases of the supply voltage.

In normal mode, the thyristor 4 is open during each positive but relative to the cathode of the half period, because at the beginning of the half period of its control electrode there is a sufficiently large amplitude of unlocking voltage coming from the secondary windings of transformers

2 and 3 (see Fig. 2, a). In this case, the actuator 6 is in the on state and signals the normal operation of the system. For sustainability, device 6 is selected with a slowdown.

on release.

When any of the phases are broken (see Fig. 2, bd), the unlocking pulses on the control electrode of the thyristor are shortened, shifted to the negative half-wave region and cannot

open thyristor. The actuator 6 at this time signals a fault in the monitored system.

The alternating phases (see Fig. 2, e), the impulses arriving from the main windings of transformers 2 and 3, are shifted in time and unlocked the thyristor only at the end of the positive half-period. The average power of the thyristor current is insufficient to turn on the actuator 6, which, in the off state, indicates a fault in the monitored system.

When the load of the three-phase network is an asynchronous gyromotor, the reactance of which changes significantly with changing rotational speed, the actuator 6 issues a fault signal when the rotation is slowed down, the gyromotor stops or is jammed, as in this case the pulses are shifted to the negative half-wave region and cannot open the thyristor.

The scheme of the proposed device is stable in operation, has good noise immunity and does not distort the vector diagram of the currents in the load.

Subject invention

A device for controlling the operation mode of an asynchronous electric motor, containing current transformers, connected to the first and second phases of the load circuit, and a phase relay on the thyristor connected in series with the actuating relay between the second and third phases of the network, to simplify and increase reliability, the secondary windings of current transformers are connected in series between the cathode and the control electrode of the thyristor.