3 phase rectifier problem

[a.bisnath]

30 year old 3 phase rectifier using thyristors -1 master , 2 slave and controller cards which are actually repairable(going or gone are those days) the master and 2 slave cards are powered by 3 individual 110 volt windings embedded in the main primary windings of the transformer,that is one 110volt winding per phase winding of the transformer which is 200amp 480 volt.the 110 volt windings are damaged (all 3),though, the main 480 volt windings and secondary windings are tested good(megger winding resistance,windings ratio)I know that the reason for the 110v winding is for the the cards to fire the SCR's at the same point for the 3 individual sine waves of the 3 phase supply and thus deliver a balanced current per phase 1 single phase supply paralelled to the cards yields unbalanced currents, one phase being very low.Might 3 single pahse transformers(480v-110v) wired across the phases work?

 

[LarryFine]

Might 3 single pahse transformers(480v-110v) wired across the phases work?

In theory, and if phased correctly (excuse me, polarity correct ), it sounds plausible.

 

[Besoeker]

Might 3 single pahse transformers(480v-110v) wired across the phases work?

Yes, but you need to ensure that the phasing is exactly right.
We (still) make firing cards for thyristor rectifiers. These have three single phase transformers to produce the voltages for synchronising and the various power supplies.
Recently we had one where a start and finish was reversed.
Confused our test department.

 

[a.bisnath]

just to say thanks

just to say thanks

the transformers did work in the wrong combination the currents can go excessively high on one of the 3 phases ,had to try different combinations to get a near balance ,but it did not balance off ,one phase was 20% off the others, the three transformers are needed or serious off balances will occur.