Zhejiang Shuyi Electric Co. Ltd

Soft start is to reduce the large electrical equipment in the start current of a device!The power of motor operation comes from 380V ac, so why does the motor have such a large starting current when it starts? General three-phase asynchronous motor starting current is in the running current of about 10 times, by ohm’s law can know U = IR, cable resistance is certain circumstances on the transmission line, the greater the current means that the greater the pressure loss of the formation on cable, we assume that come out from the transformer secondary voltage is 400 v constant voltage at the input to the electrical equipment may only The 370 v. The transformer with other electrical equipment in the normal operation of the voltage suddenly reduced in the case, because the output power of the asynchronous motor depends on the load P, the motor output power P value of the case P=1.732U voltage reduction current value will continue to increase the voltage loss formed on the cable. Other motor power protection or overheating protection may trip.

If you need a soft starter Zjshuyi is a good choice

Soft starter is a novel motor control device that integrates motor soft start, soft stop, light load energy saving and various protection functions. Its main composition is a three-phase parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor. Different methods can be used to control the conduction angle of the three-phase parallel thyristor, so that the input voltage of the controlled motor changes according to different requirements, and different functions can be realized.

Common soft starter mainly electronic, magnetic control and automatic liquid resistance type. Electronic thyristor voltage regulating type for the majority. Thyristor soft starter is three groups of thyristors connected in parallel between the power supply and the motor in positive and negative direction. It realizes AC voltage regulation by microcomputer to trigger the conduction Angle. Thyristor soft starter can be started by ramp voltage type, ramp jump voltage type and current limiting type. Magnetically controlled soft starter is a soft starter composed of three-phase saturated reactor which is connected in series between power supply and motor. When the motor is started,

the excitation current of the control winding of the magnetic amplifier is adjusted by the word control board, and the starting voltage drop is adjusted by changing the reactance value of the saturation reactor to realize the soft start of the motor. No matter the thyristor type soft starter is magnetically controlled, the output voltage can only be adjusted when the soft starter is started to control the voltage drop and limit the starting current. General soft starter can not adjust the frequency of the power supply, it can not start the motor from zero frequency and zero voltage like the frequency converter, to achieve no impact start. In fact, when the soft starter starts the device, it must produce a certain impact current; The voltage and current change curves of ramp voltage-controlled soft starter are shown in Figure

1. When the thyristor type soft starter starts with slope voltage, it should make the soft starter output an initial voltage at the beginning (the initial voltage can be adjusted between 80 and 280V), so that the motor produces an initial torque sufficient to overcome the static friction of mechanical equipment, and drag the equipment to start rotation. The starting current is LS. Microcomputer control, continue to increase the output voltage to accelerate the motor. When the output voltage of the soft starter Is close to the rated voltage, the motor has reached the rated speed and Is Is reduced to the load current In. At the end of t1, the soft starter outputs rated voltage and sends out bypass signal to make the bypass contactor close, the soft starter stops output voltage and the motor turns to normal operation. Soft start initial torque can be given the initial voltage and start time, line adjustment, control start current 2~4.5 times the rated current of the motor.


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