Star Ring Sizing

[petronila]

Dear All

Usually, in large motors that are internally connected in parallel stars (3Y-4Y-5Y-6Y, etc.) we found all stars connected with a star ring. When repairing, make sense to use the same wire/conductor size that we found in the original winding, but there are some cases where repair shops receives a bare core or a damage winding without connection leads and you don´t know the wire/conductor size of that star ring.

Do you know a good approach or rule of thumb that might help with the star ring wire/conductor calculation?

Thanks in advance

Petronila

 

[waross]

Is it needed?
It may only carry current if there is a fault in one or more star groups, and then may serve to make the damage worse.
In any event, I would evaluate the star ring on the basis of the expected or desired current due to a winding fault.
You may want added current during a fault to ensure faster tripping and possibly less arcing damage.
But, shorter time and more current or possibly less current and much longer tripping time and possibly no tripping.
Your call.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

In theory, the neutral ring current is supposed to be zero for balanced phase currents but in real life ....

I use one phase conductor total area for star ring, mostly for ease of brazing. Too small a diameter for the neutral ring means the brazing of the coils is a pita.

Muthu

http://www.edison.co.in

 

[waross]

but in real life ....

I'll buy that.
I've seen too much "but in real life ...." that shouldn't have happened.

Bill
--------------------
"Why not the best?"
Jimmy Carter