When a high-power motor starts, the starting current is large, which will cause serious fluctuations in the grid voltage. In order to solve this problem, when the speed regulation is generally not required, a soft starter can be used to reduce the voltage.
However, the reduction of the starting current during the step-down starting will also greatly reduce the starting torque, so it is not suitable for starting with a rated load, but generally suitable for no-load or light-load starting.
When the motor needs to be started with load or has high requirements for speed regulation, the frequency converter is generally used to start, which can reduce the starting current under the premise of ensuring a larger starting torque. In addition, both step-down and constant voltage-frequency ratio (constant air-gap magnetic flux) can adjust the speed, but the step-down speed adjustment will soften the mechanical characteristics of the motor, and the speed adjustment range is small.
The constant voltage frequency ratio has a large speed regulation range, and the mechanical characteristics of the motor are hard.
The constant voltage frequency ratio speed regulation has so many excellent special effects, why not apply it on a large scale, the answer is that the cost of the soft starter is very low, the AC power voltage regulation circuit can be realized, and the high-power inverter is expensive.
The possible reasons why the starting current of the motor is still relatively large after the soft starter is used are as follows:
1. Because of the motor system controlled by soft start, the capacity of the motor is relatively large, mostly ranging from more than 75KW to several hundred kilowatts;
2. Most of the motor systems controlled by soft start are hard loads. If the current limit start method is adopted, it should be set to at least twice the rated value of the motor or three times the rated current value, so as to basically meet the technological requirements of the system.
Reasons why the motor soft starter cannot start:
The parameter setting is unreasonable
Solution: Re-adjust the parameters, increase the initial voltage appropriately, and lengthen the time appropriately.
Full load start at start
Solution: try to reduce the load when starting.
Motor phase loss
Solution: Check the motor and peripheral circuits.
The main component thyristor in the soft starter is short-circuited
Solution: Check whether the motor and grid voltage are abnormal, and contact the manufacturer to replace the thyristor.
Filter board breakdown short circuit
Solution: replace the filter board.
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