A controllable compensation type full torque energy-saving soft start device for asynchronous motors

Abstract

The invention relates to an asynchronous motor controllable compensation type full-torque energy-saving soft start device. In the device, an air switch, a three-phase starting capacitor and the alternating-current input end of a three-phase rectifier bridge are connected in series and then are connected in parallel with leads of each phase of a controlled motor. A three-phase compensation capacitor is connected between a three-phase starting capacitor and a three-phase rectifier bridge in parallel, and the direct-current output end of the three-phase rectifier bridge, the power resistor, the collector electrode and the emitting electrode of a power transistor are sequentially connected in series. The control circuit is connected to the two ends of the three-phase rectifier bridge in parallel, and the signal output end of the control circuit is connected with the base electrode of the power transistor. Compared with the prior art, the device has the advantages that the starting currentis inhibited, and the starting torque is not reduced, the voltage fluctuation of a power grid can be effectively overcome, harmonic interference is avoided, the power factor of the motor is increasedto about 1, the line loss is reduced to the maximum extent.

Description

technical field [0001] The invention relates to motor energy-saving control equipment, in particular to a controllable and compensated full-torque energy-saving soft start device for asynchronous motors. Background technique [0002] The production equipment driven by asynchronous motors is widely used in the industrial field. For asynchronous motor loads with large capacity, soft starters are often used to realize the soft start of the motor. However, soft starters have two shortcomings that are difficult to make up for. One is the low power factor. , the current waveform is poor and the harmonic content is large when starting, so capacitors cannot be configured to realize reactive power compensation, resulting in a substantial increase in line loss. Second, the starting torque is small and the starting speed is slow. At the same time as the starting current, the starting torque of the motor is greatly reduced at a square rate, resulting in a slow start. For important produ...

AI Technical Summary

Problems solved by technology

[0004] 1. Several existing soft-start technologies, almost all soft-start solutions are at the expense of motor starting torque, resulting in slow or even difficult start-up of loads. Many important auxiliary equipment such as converter stations and power plants often encounter main engine In the case of failover to the standby machine, however, the existing soft starter starts slowly, which often leads to serious accidents caused by the slow start of the above-mentioned important equipment

To overcome this problem, it is sometimes necessary to use a frequency converter or a wound rotor asynchronous motor, which doubles the cost of the equipment;

[0005] 2. In the prior art, when starting the motor, although the starting current of the motor is greatly reduced, since they all adopt thyristor chopper voltage regulation or autotransformer voltage regulation, these devices themselves are inductive, so the power factor is still very low. The current is not large, but the instantaneous fluctuation of the grid voltage is often obvious, and sometimes it will cause the failure of other sensitive electrical equipment to shut down;

[0006] 3. Most of the existing soft starters use thyristor chopping and voltage regulation, which has a large harmonic content, and harmonics have become a major public hazard in the power system;

[0007] 4. The existing asynchronous motor equipped with a soft starter cannot cooperate with the capacitor due to the pulse-like voltage of the thyristor chopper circuit, plus the cost of the soft starter, and the cost of adding a capacitor externally is high. In addition, due to the motor’s Self-excitation problem, the compensation power factor at the motor end cannot be very high, resulting in large line loss of the motor in the prior art,

[0008] 5. The soft starters in the prior art are all connected in series with the controlled equipment. Once a fault occurs, the controlled motor will be stopped directly.

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