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dY and dD from the same transformer. Will it work ?
2

dY and dD from the same transformer. Will it work ?

dY and dD from the same transformer. Will it work ?

(OP)
I am planning to build a 500 KVA testing trafo for testing 6.6 KV and 3.3 KV motors for no-load and locked rotor losses.

The primary of this would be 415 V, 50 Hz, delta. The secondary would be 6.6 KV wye (neutral grounded) and 3.8 KV delta from the same HV winding whose all six leads will be brought out to enable the switch over.

The primary would be fed from a continuously variable 0 - 415 V, motorized variac (stepless auto) to control the inrush current.

Will this connection of dY and dD from the same trafo work ? Any pitfalls ?
 

RE: dY and dD from the same transformer. Will it work ?

(OP)
Also, I plan to install 3 dough-nut type CT's at the base of the HV bushings for measurement and protection. Will installing the CT's at the bushing bases affect their accuracy ?
 

RE: dY and dD from the same transformer. Will it work ?

Why not build an autotransformer secondary instead of the three winding transformer

RE: dY and dD from the same transformer. Will it work ?

6.6kV may be a little high for an autotransformer. Building a continuously variable auto transformer is considerably more difficult than building a conventional transformer.
 

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

RE: dY and dD from the same transformer. Will it work ?

edison123, there is no reason why you can't have a transformer with all six ends brought out and the windings sometimes connected in wye and other times connected in delta.  The windings will have to be fully insulated for 6.6kV, but other than the need for six bushings instead of three or four you shouldn't have any trouble.  CTs on the bushings are extremely common.

RE: dY and dD from the same transformer. Will it work ?

To answer the original question: Yes, transformers with one delta primary and two secondaries, one delta and one wye, are used all the time in larger drives. But, as davidbeach says, it would probably be more practical to bring out all six ends and do the switching induction motor style.

Question: Do you really need different connections? Is that to get two voltage ranges?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: dY and dD from the same transformer. Will it work ?

(OP)
Thanks davidbeach for that confirmation.

I was a bit worried whether dD would have some circulating current issues.

RE: dY and dD from the same transformer. Will it work ?

(OP)
Yes, Gunnar. I do rewind of 3.3 KV, 6.6 KV and 11 KV motors. I wanted one transformer for 3.3 & 6.6 KV and another one for 11 KV to cut cost.

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