Trafo vector group
Trafo vector group
(OP)
Hello All.
Could you please explain: why trafo mnf's build in US ( and not only in US) trafos YD1 and YD11 and many Eroupean mnf's YD5 and YD7.
What is a reason?
Thanks in advance.
Best Regards.
Slava
Could you please explain: why trafo mnf's build in US ( and not only in US) trafos YD1 and YD11 and many Eroupean mnf's YD5 and YD7.
What is a reason?
Thanks in advance.
Best Regards.
Slava






RE: Trafo vector group
RE: Trafo vector group
RE: Trafo vector group
UK practice tends to have dYN1 for generator step-ups, Dyn11 for distribution transformers, plus less common ones like ynYN0, and various oddities with other vector groups.
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If we learn from our mistakes I'm getting a great education!
RE: Trafo vector group
I asked not only about GSU, common practic as you saied is Ynd1,distribution trafos are Dyn11 or Ynd11, as I understand because inductive load.
but I see excitation trafo for the generator used with vector group 7 ( or 5 ) and same for rectefire bridge.
What is a phisical reason.- OK secondry voltage is lag primary on 210 ( 150) deg. For what?
Best Regards.
Slava
RE: Trafo vector group
There is nothing 'special' about any of the configurations. A Dy1 transformer can (depending upon construction) be fairly easily converted into a Dy11 transformer by changing the wiring at the primary of the transformer.
As to why anyone would construct a Yd5/Dy5 or Yd7/Dy7 I have no real idea. I have never seen any of these in the field in Australia, New Zealand or South Pacific. The only 'hand waving' explanation I can think of is that some manufacturers found it easier and less expensive to wire their transformers in this way. It makes no practical difference for the loads at the secondary as the voltages are still in a positive sequence.
As for their use in rectifiers, I cannot see this. For a twelve pulse rectifier a 30 degree phase shift is needed between one six pulse bridge and the other. This is provided satisfactorily by a Dy1 or Dy11. OEMs quite often design a twelve pulse rectifier using a transformer with a dual secondary and a 30 degree phase shift between the secondaries, and it is quite common practice for rectifiers where the DC has to be isolated from ground. The 'normal' practice is to use a Dd0y1 or Dd0y11 but there is nothing stopping the design being a Dd6y5 or Dd6y7; but I can think of no practical reason why this would be done.
RE: Trafo vector group
At one of our plants the standby source (one Dy from the 500kV reference) was 30° ahead of the normal plant aux load bus (two Dy from the 500kV reference). Doing a motor bus transfer from normal to standby bus meant waiting for the motor bus to slow down enough to slide back 330° relative to the standby source before before the transfer relay would close into the standby source. That took about 45 power system cycles and we'd loose a couple of critical motors. Rewired the standby transformer so that it was 30° behind the normal source and now the transfer takes less than 15 power system cycles and the motor bus drifts back about 40° but the 10° out of phase with the new source isn't a problem. Now we don't loose any motors going from normal to standby.
Back to normal is now more problematic but we get to schedule when it happens while the normal to standby transfer always happens at a bad time. Better to have the unwanted transfer happen flawlessly and the scheduled transfer need to have a motor shutdown and restarted than loosing motors at the same time we've lost the 500kV system.
RE: Trafo vector group
RE: Trafo vector group
Maybe I have fallen into bad habits - by the way I was taught, for a GSU transformer the delta is the primary hence it appears first. Anyone know what the 'official' position is on this?
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If we learn from our mistakes I'm getting a great education!
RE: Trafo vector group
As per my understanding excitation trafos and interposing trafos have Yd5 and Yd7 connections.Yd5 and Yd7 are 180 out of phase with Yd11 and Yd1
RE: Trafo vector group
I would like ask next Q on this issue.
OK, 5 and 7 group is some exotic.
Why for GSU used YD1 and for distribution YD11?
Must be some reason!!!!
Best Regards.
Slava
RE: Trafo vector group
"In case of distribution transformer the load current remains lag due to inductive load so the phase voltage to coinside with laging current the D to Yn 30 (lagging in voltage) used. the same case is for generator transformer".
What do you think about it?
RE: Trafo vector group
For ANSI delta-wye transformers, the low voltage winding lags the high voltage winding by 30 degrees regardless of delta-wye, wye-delta, or anything else. This can result in YD1 or YD11 depending on the application.
RE: Trafo vector group
Thanks a lot for your help.
I think, I finished with this issue.
Best Regards.
Slava
RE: Trafo vector group
As my knowledge goes delta is used in GTs to avoid zeroesquence currents get in to generator stators in the event of a LG fault on transformer HT side.Generators cannot stand zerosequence currents.In DTs HV delta helps in reducing fault currents without increasing cost from uniform insulation.The quote you mentioned is from some book? Can you give some reference as I could not understand the logic or advantage in it.
RE: Trafo vector group
Thanks a lot for your time and explanation.
The quote aren't from book. it's from:
http:
My Q. come from my freinds from Russia: " What is standard groups in the word, why used YD1 and YD5/7"
Russia used only YD11 group.
Best Regards.
Slava