Star Delta connection

[m sleem]

For star delta motor starter, since we are using magnetic circuit breaker so the overload relay shall be installed accordingly, if we installed the overload at the main branch do we need to install also at delta branch?

 

[retirede]

What is your objective? Use one OL relay instead of two?

The two-relay setup provides OL protection when in wye configuration. You’d lose that with a single OL.

 

[Jraef]

What is your objective? Use one OL relay instead of two?

The two-relay setup provides OL protection when in wye configuration. You’d lose that with a single OL.

Correct. This scheme with the 2nd OL relay is only for the people who run a star-delta wound motor is start continuously, at essentially 1/3 load. We don't do that here in North America, but I happen to know it is done in a number of other countries as a way of "saving energy" if the load is really light. It only makes sense if the original motor was selected and designed for a very large task that is rarely performed, so the motor needs to run in the severely limited capacity most of the time.

 

[m sleem]

Correct. This scheme with the 2nd OL relay is only for the people who run a star-delta wound motor is start continuously, at essentially 1/3 load. We don't do that here in North America, but I happen to know it is done in a number of other countries as a way of "saving energy" if the load is really light. It only makes sense if the original motor was selected and designed for a very large task that is rarely performed, so the motor needs to run in the severely limited capacity most of the time.

Like jet fans at indoor parking spaces ?

 

[retirede]

Correct. This scheme with the 2nd OL relay is only for the people who run a star-delta wound motor is start continuously, at essentially 1/3 load. We don't do that here in North America, but I happen to know it is done in a number of other countries as a way of "saving energy" if the load is really light. It only makes sense if the original motor was selected and designed for a very large task that is rarely performed, so the motor needs to run in the severely limited capacity most of the time.

It could also save the motor if a failure of some sort leaves it running in wye. Just a theory, I don’t think I’ve ever seen it happen.