If the motor is not to full speed by the end of the PF softstarter ramp time when will the bypass engage?
The PF soft starter product provides an enhanced up-to-speed detection scheme. In this scheme the back EMF of the motor is calculated as a percent of applied voltage and used to detect up-to-speed. The calculation is made every firing period and on each phase In normal starting mode the PF soft starter product will monitor this information and determine when the motor is at running speed. Once the motor is at running speed the bypass is engaged. The internal bypass is referred to as an arc-less contactor. There are many protection features built-into the PF product to ensure the contactor never sees excessive current or make / breaks currents.
The following information assumes abnormal current conditions and how the internal bypass reacts. The PF soft starter internal bypass contactor is operated in such a way as to never make or break motor current. This is done by always firing the SCR's while opening and closing the bypass contactor (brief parallel operation). In cases where the motor is not at full speed by the end of the programmed time the SCR's will continue to fire at full voltage. During that time once the current falls to 105% of the PF product maximum frame amp rating the internal bypass is engaged. If at any time the phase currents exceed 120% of the frame rating while in internal bypass mode the SCR's will be turned on again.