Control Panel Star Delta Starter

[TomS]

Hello all. I’m after a bit of advice. Daft question I’m sure but when wiring a star delta starter in a panel is it necessary to use the electrical interlocks, i.e for the coil of the delta contactor, would you take the wire through the N/C of the Star contactor first?

 

[Andy-1960]

Yes, the delta contactor should be electrically and preferably mechanically interlocked with the star contactor.
If the delta contactor were to energise with the star contactor stuck or welded in, this would result in a dead short across all three phases.

 

[Deleted member 26818]

One needs to open before the other closes.

 

[PEG]

Which is why the uninitiated,can on occasion,open up the panel,and in an effort to "test" or "jog" a troublesome motor,get round to manually poking two contactors at once...and get a fuse time/current demonstration

 

[Andy-1960]

Which is why the uninitiated,can on occasion,open up the panel,and in an effort to "test" or "jog" a troublesome motor,get round to manually poking two contactors at once...and get a fuse time/current demonstration

Yes coupled with an almighty bang and a flash!

 

[bomjac]

Screw up the timing and you'll get an almighty bang.

Had a 300kW HPU starter go "boom" on a job because the time between wye & delta was too short - when the delta came in the wye contactor was still arcing which destroyed both contactors - TWICE before the pre-comm guys figured out the problem along with Schneider.

 

[Bobster]

Screw up the timing and you'll get an almighty bang.

Had a 300kW HPU starter go "boom" on a job because the time between wye & delta was too short - when the delta came in the wye contactor was still arcing which destroyed both contactors - TWICE before the pre-comm guys figured out the problem along with Schneider.

Can you expand on that please, it doesn't quite make sense in what you're saying.

 

[bomjac]

Wye is the US term for "Star"

Some companies make a "1 size fits all" cubicle. This can be used as master contacter with 2 others contactors which can be programmed via the motor manager unit. These can be programmed as fast / slow, star / delta, heat stage 1, heat stage 2 etc.

The big problem with these was that there were no mechanical interlocks.

Whoever set the starter up had not allowed enough time between star dropping out and delta closing. So when the changeover between star and delta happened the star contactor was still arcing across he contacts at the same time as the delta closed.

Line to line fault on a 300kW, 690V contactor is not a good idea.