How to select Soft starter?

1) Base on heavy load and light load. Choose different types soft starters according to the different load characteristic.

If the load is centrifugal pump (fire pump, spray pump, water pump, etc.), we need to use the pump control function to reduce water hammer phenomenon occurs during the impact of starting and stopping, therefore, we should select the soft starter with pump control function, and it's better if it has underload or phase reversal protection.

If the load is fan, use the soft start to reduce belt wear and mechanical shock, and brake torque during shutdown.

If the load is mixer, crusher, elevator, etc., use soft starter's dual ramp start and preset low speed operation to avoid mechanical damage.

If the load is transportation equipment, use soft start and preset low speed features to achieve smooth start/stop, soft stop eliminates drag anti-inertial impact caused by free parking.

2) Base on the motor power, current and load characteristic to choose the soft starter. Generally, the soft starter capacity slightly larger than the motor operation current capacity, and increase a step power for some heavy loads, such as: crusher, ball mill, hoist, long belts, mixers, fans, etc.

3) Other aspects, we should consider the protection functions, such as over-current, over voltage, single ground fault, upper and lower phase loss, phase unbalance, phase reversal protections. For overload protection, the soft starter needs additional thermorelay protection.

Soft starters are allowed to work at its rated load in long-term, use the bypass contactor to short it after start finished, then we should pay attention to whether the motor has thermal overload protection in its circuit loop. In practical applications, if the working condition allows, we can use a soft starter to start several motors with the capacity bigger than the largest motor starting load, this will reduce investment costs significantly.