SU235149A1 - DEVICE FOR STARTING AND BRAKING ASYNCHRONOUS - Google Patents

Description

A device is known for starting and braking an asynchronous electric motor, in series with the stator winding of which control valves are connected, and a parallel bypass thyristor. In this case, the controlled dynamic braking is carried out due to the rectified half-wave current flowing through the two phase windings of the engine.

The proposed thyristor device is more perfect, since it sharply reduces coasting when the engine is braked by increasing the braking torque in the high-speed zone. This is achieved in that a half-wave current is passed through the stator winding, which is obtained by rectifying the voltage of the two phases of the network, the order of alternation of which is inverse to the phase rotation in the motor mode. In this case, the first harmonic component of the rectified current creates an inhibition braking mode while maintaining the dynamic braking mode of the constant current component.

FIG. 1 shows the proposed device; in fig. 2 is an oscillogram of engine speed (ha) and phase current (/ f) when the engine AO2-12-4 is braked by the device shown in FIG. one; in fig. 3 - the device providing smooth braking of the asynchronous motor without vibrations in the stopping position; in fig. 4 is an oscillogram of the motor speed and phase current during engine braking А02-12-4 with the device shown in FIG. 3; in fig. 5 - device for starting and braking of low-inertia drives; in fig. b - oscillogram of engine speed and phase current during engine braking А02-12-4 (without additional small masses) by the device shown in

FIG. five.

The proposed device for starting and braking the motor 1 (Fig. 1) for any connection of its stator winding consists of four starting thyristors 2, 3, 4 and 5

included in the anti-parallel circuit in two phases, and two brake thyristors 6 and 7, connected crosswise between the two phases of the network and the two terminals of the stator motor winding. The motor is started and its operation is performed by opening thyristors 2, 3, 4 and 5, which connect the motor to a three-phase network. For braking, the control sigal is removed from the starting thyristors and through the time required for them

closure (of an i-loop in the ac circuit), an opening signal is applied to thyristors 6 and 7. The current from the two phases of the network is rectified and fed to the phase windings of the stator, disconnected by starting thyristors from

klyucheppu phase winding of the engine. Due to the cross-start of the thyristors, the fundamental harmonic component of the mean of the current of the current creates the effect of inhibition by the inclusions. The magnitude of the current is adjusted by the opening angle of the brake thyristors. Braking occurs intensively (see Fig. 2) with a minimum engine overrun in the process of stopping. The device can be used when connecting the motor windings both in a "star and in a" triangle.

In the practice of precision machine-tool construction, an unstretched, smooth braking of the engine is often required. This is achieved by applying symmetrical dynamic braking circuits characterized by the same magnitude and direction of current in all three phases of the engine. In this case, the proposed device can be modified as shown in FIG. 3 for the case of connecting the motor windings into a delta.

The motor starts to rotate when opening thyristors 2, 3, 4, 5 and 6. At the same time, it is connected to the network, and its phase windings are connected in a "triangle." To translate into braking mode, all the starting thyristors are locked by removing the control signal, and the brake thyristor 8 is opened. At the same time, a rectified current flows through all sequentially connected windings in the positive half-period Vas, the thyristor 7 shunt the stator windings, smooths rectified GOK. The flow of the same magnitude and direction of the current in all phase windings of the engine provides a mode of symmetrical deiamine deceleration, characterized by a small, smoothly varying braking torque and a decrease in the vibrations of the rotor of the engine in the process of stopping.

The smooth braking process of the engine is illustrated by the waveform in FIG. four.

For deceleration of low-inertia synchronous drives, the short-circuit winding mode with the subsequent passing of a two-phase current through it is very effective. FIG. 5 shows a variant of the proposed device in relation to this case. Start and work

the motor is carried out when opening thyristors 2, 3, 4 to 5. For braking the engine thyristors 2 and 4 are turned off and short-circuit thyristors 6 n are turned on 7. A short circuit of two windings occurs, which leads to a 10–20% reduction in motor speed (see Fig. 6). At the same time, the connection of two phase windings in parallel and voltage generation and Ug by thyristors 6 and 7 provide a current flowing through the stator winding with a large constant component, which leads to an increase in the braking effect.

Thus, the proposed thyristor device can be modified in each particular case to ensure optimal braking. In all devices, the counter-parallel connection of the thyristors can be replaced by a single symmetric thyristor.

Subject invention

ycrpoiiciBo for starting and braking an asynchronous motor, in series with

The stator winding of which incorporates controlled valves and a parallel shunt thyristor, characterized in that, in order to reduce engine run down during braking, an additional thyristor is used, which, like the shunt thyristor, is connected non-crest between two phases of the network and two phases engine

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