ABB Restarting with motor idling

Restarting with motor idling

- Attempting to restart the motor before it

has come to a full stop will cause a current peak that theoretically can reach twice the

current compared to starting the motor from a standstill. This can result in welded

contacts.

Star delta (wye-delta) starters

Change over time between star and delta

- Setting the change over time between star and delta too short will not allow the

motor to reach 80-90% of its nominal speed. This will cause the star contactor

to break a higher current than expected. If the starter stays in the star position for

too long of a period; this will increase the stress of the star contactor because the

star contactor is mainly sized for the short time current rating.

- The change over time between the star and delta is important. If no timer or other

device is used to get an idle time between opening of the star contactor and closing

of the delta contactor, there is a risk that the arc inside the star contactor could

remain and create a short circuit. If the elapsed time is too long, the motor starts to

decelerate and the delta closing will create a higher current peak than expected.

This can result in welded contacts. Generally the idle time should not exceed 50

ms. When AF is used no separate time delay is needed.

Product coordination

Lack of product coordination with fuse or breaker missing or wrongly sized can

cause excessive contact wear or lead to welded contacts.

For more specific information regarding short circuit protection coordination please see our technical catalog

1SBC1001122C0202. section: General technical data.