Star Delta CB trip on delta

[Guest]

Have had a Star Delta Starter in situ for a number of years...It now trips the CB when changing over to delta... do you think that this is due posibly because as the motor gets older (the enviroment is chlorine also) the synchronous speed or 90% is not reached in star before the delta change over and as such upon change over the extra transients are now tripping the CB. I personnally would like to change it to soft starter, but i need to justify the change over costs....etc... ;d;

[jraef]

If it was working fine and nothing else was changed, I think your hypothesis has merit. Open Transition Y-Delta spikes can be very high and dangerous to other equipment in your entire facility. The worst effect comes from the motor slowing down slightly during transition, allowing the Delta connection to be made after the motor has lost momentum. That coupled with the inherent phase shift that occurrs going from Y to Delta, and you have the motor windings being out of phase with the line. As your motor got older, the bearings and other mechanical components in the load are wearing, so it may require just a bit more starting torque. This increases that momentum loss and the transition spike gets worse rapidly.