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Can the LH4N unit catch a spinning load?

LH4N modular soft starts provide gradual starting of asynchronous motors by using solid state power devices to control the voltage applied during acceleration. By reducing the voltage supplied to the motor during acceleration, the amount of starting torque is reduced.
If the load is already spinning when the soft starter is started, the voltage will ramp to full voltage as usual.
Much like a standard full voltage starter, there should not be a problem starting a motor that is already spinning under most circumstances. If the motor is already spinning in the correct direction when the soft starter is started, it may appear that the LH4N is ``catching on the fly`` due to motor slip and relatively low starting torque.
However, if the inertia is very high in the reverse direction, there may not be enough starting torque available to turn the motor without tripping overloads. Also, if a running motor is turned off and on very quickly, there could still be voltage on the motor which would be out of phase with the line voltage. This could cause short circuit protection to trip or cause the motor speed to change very quickly. Both of these issues are similar to using standard full voltage starters.

CTA-ID : 7519
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