How to select the right motor soft starter

- Jul 16, 2019-

Now that many motors use a soft starter as a start protection device, how do soft starters be selected? Here's a look at what Winston Electric says.

1. Select the motor soft starter note whether the load is standard load or heavy load. Different types of starters are selected depending on the nature of the load.

If the load is centrifugal pump (fire pump, spray pump, water pump, etc.), then the pump control function should be used to reduce the occurrence of the system water hammer phenomenon caused by the liquid flow shock when starting and stopping, so it is necessary to use a soft starter with pump control function, such as another underload protection or phase inverted protection is better; The load is ventilator, the use of soft start function, reduce belt wear and mechanical impact, and can use the brake torque function when stopping;

The load is a blender, crusher, lifter, etc., which uses double ramp starting and pre-set low speed operation to avoid mechanical damage. The load is the conveying equipment, can use the soft start and preset low speed function, to achieve smooth open and stop, soft parking to purify the drag system anti-inertia shock due to free parking, to avoid product shift and liquid overflow;

2. According to the nominal power of the motor, current and load nature of the selection of starter.

General soft starter capacity is slightly larger than the motor operating current can be, some heavy load on the cement plant should be increased a gear of use, such as: crusher, ball mill, lifter, long belt, blender, fan, etc., at the same time due consideration of cooling factors.

3. Other aspects, but also to consider whether to protect complete functions.

Such as overcurrent protection, overvoltage protection, single ground protection, upper and lower cut phase protection, three-phase imbalance protection, phase inverted protection, etc. Without overload protection, the relay protection must be heated separately.

Some motor soft starters generally do not short-circuit protection, need to be coupled with a fast fuse and match the capacity of the thyristor, it can make the thyristor in the connection load when the short circuit is protected, low-voltage circuit breakers generally can not protect the soft starter. Inlet reactors can limit harmonic interference from the main spline, and incoming reactors are recommended when several starters are connected to the same power supply.

Motor soft starter to the motor wiring to pay special attention, most of the three out of line, but some products also have 6 out of line. The soft starter can be installed in a system with a power factor compensator, but the capacitor must be located on the power feed side of the soft starter to avoid the capacitor discharge damaging the thyristor of the soft starter and inductive coils between the power supply and capacitor.

The motor soft starter allows long-term operation under rated load conditions and can be shorted after starting with a bypass contactor. After cutting, we should pay attention to whether the motor running circuit still has overload thermal protection function. In the process of practical application, if the process conditions permit, with a motor soft starter to start multiple motors, its capacity should be considered according to the larger starting load in the motor, can greatly save investment costs.

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