we have installed star-delta motor starters for water pumps with 22.0kW AC 3-phases drives.
In the moment of switch from star to delta the circuit breaker before always release (trip).

Does anyone know this problem and can help me?

(Hint: motor connection is ok)

 

Is this a new or existing installation?

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

Sounds like the star and delta contactors are coming together. There should be a mechanical interlock between them and a star-delta timer controlling the switching.

 

Is this a "home built" motorstarter or a prefab?
There must be a short delay between the switching.

 

Star-Delta is an open transition scheme. A time r with a N.C.T.O. contact is employed. (Hint: motor connection is ok) I am going to asked an off the wall question. If the connections are good; are the starters as recieved from the factory wired properly ? Verify the factory work. Is the transition set properly? It would be good to hear the outcome of the troubleshooting?

Regards,
Paul Dackermann

 

Although you have checked the motor connections, it has happenned to me twice before when the motor terminals were wrongly marked. You get a resistance across say v1 and v2 which makes you think that it is correct, but in reallity they have been swapped, ie v1=v2 and v2=v1. What happens is that it will start in star ok but when it changes delta you have one phase out of sync, which causes an over current. The only way i found out how to check for this was to swap them one at a time and then swapping them back before trying the next pair.