Dual Delta-Wye Secondary Transformer Question

[electromike]

Why would a medium voltage (2300v)AC variable speed drive have a dual secondary (6 leads out) supply transformer feeding the the front side (12 pulse rectifier)of the drive?
Is this transformer needed of does it serve some added benifit?

 

[davidbeach]

Hard to feed a 12 pulse rectifier with only 3 leads.

 

[rbulsara]

Dual secondary, normally one delta and one wye, provides effectively 6 phase input to a 12 pulse rectifier, due to phase angle difference between delta and wye secondaries.

Higher pulses of rectifier gives you less ripples in the DC output. 3 phase input rectifier will give 6 pulse output. Likewise you can have 18 pulse and 24 pulse rectifiers, if you can feed with more inputs differing in phase angles, using appropriate no of secondaries shifted in phase with each other.


Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

Oh, there is a side "benefit" of electrical isolation, as it will act as isolation transformer as well but that is not the reason it is there.

Rafiq Bulsara

http://www.srengineersct.com

 

[electromike]

Thanks rbulsara.Your answer makes great sense.

(David don't you think your answer was a tad-bit too general?)