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ijanto
Member

Join Date: Jul 2012
Posts: 7

Generator Transformer Phase Sequence Problem RYB-BYR

07/23/2012 12:15 AM

Dear all,

I have one important question on the phase sequence of transformer in this case generator transformer. My question as below:

Existing transformer is a 325MVA Ynd1 (phase sequence: RYB). The spare transformer is a 325MVA Ynd1 (phase sequence: BYR). As you can see there is a major different

between the transformer. In the event of existing transformer failure, we are planning to use the 325MVA spare transformer.

My question is, if we decided to connect

B phase generator side to R phase generator Transformer side,

Y phase generator side to Y phase generator Transformer side

R phase generator side to B phase generator Transformer side,

What will happen at the HV output of generator transformer?

One of the OEM said The generator transformer will be seen to have a Ynd11 vector group instead of original Ynd1 if Gen & Gen Tx is connected using configuration 2. However, they are yet provide any proof. If the spare can be used, what other things that we need to look at i.e. protection. Thank you all for your help.
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Tornado
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Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

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#1

Re: Generator Transformer Phase sequence problem RYB-BYR

07/23/2012 1:16 AM

I don't think this picture is fully enough described yet.

One hopes that only the coloring is in reverse rotation, not the circuitry itself.

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ijanto
Member

Join Date: Jul 2012
Posts: 7
#2
In reply to #1

Re: Generator Transformer Phase sequence problem RYB-BYR

07/23/2012 2:14 AM

The configuration as below for better explanation. As you know,

for 325MVA 275kV/15kV transformer, the modification required on the HV and LV side will be massive if still need to connect Red to Red, Blue to Blue and Yellow to yellow phase. I just want to know what is the outcome at the HV side incase i just directly connect B to R, Y to Y and R to B at the LV side. Anyway, thanks for the reply.

Regards

Shah
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raghun
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Join Date: Jan 2010
Location: Hyderabad
Posts: 343
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#4
In reply to #2

Re: Generator Transformer Phase sequence problem RYB-BYR

07/23/2012 5:23 AM

There shouldn't be any problem.

As I see you are having reversed connections at both generator and grid ends. Thus, the vector group remains unchanged.

In any case, since it is generator, phase matching with the grid can be achieved before synchronistion.

Do you have GCB at 15kV generator terminals or you synchronise at 275kV!!

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Joshi
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Join Date: Oct 2007
Location: India
Posts: 1246
Good Answers: 34
#3

Re: Generator Transformer Phase sequence problem RYB-BYR

07/23/2012 2:53 AM

All downstream rotating machinery will reverse direction of rotation,
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Bibo92004
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Join Date: Jul 2011
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Good Answers: 2
#5

Re: Generator Transformer Phase Sequence Problem RYB-BYR

07/23/2012 10:17 AM

My friend, all you need to do is test the connection for phase sequence and vector group. If it is matching what you expect then go for it... otherwise you can't depend in some theory to do it because generator will never be able to synchronize with the grid if vector group and phase sequence are not matching. So to save you some time I suggest you to test your transformer and maybe you need to go for a commissioning test instead to test the whole set.

Good luck
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ijanto
Member

Join Date: Jul 2012
Posts: 7
#6
In reply to #5

Re: Generator Transformer Phase Sequence Problem RYB-BYR

07/23/2012 9:03 PM

Thanks all for your input. Most probably I will just ask one of the manufacturer to carry out the test for us when we bought the spare transformer. If it does not satisfy our requirement then most probably we need to buy additional transformer with different phase sequence. I will let you guys know the outcome.

Anyway I have another question, since this is a generator transformer, should the generator be able to shift the phase angle to match the grid system voltage during synchronization assuming the gen tx vector group will change from Dny1 to Dny11. Thank you

Regards,

Shah
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RAMConsult
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Engineering Fields - Power Engineering - New Member

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#7

Re: Generator Transformer Phase Sequence Problem RYB-BYR

07/24/2012 12:17 AM

To answer your second question first, the generator has no idea what the phase shift is through the transformer, nor does it care. As long as the frequency, phase rotation, and voltage match then it will synchronize.

Your first question requires more analysis, and you were wise to not simply connect it and have a go at it. There may be a reason why the rotation is reversed and it may have to do with the internal connections of the windings, or it may be cosmetic. If it is cosmetic then your diagram 2 works fine since there is a straight through connection for each winding; i.e., the polarity dot on LV winding R is in the same location as the polarity dot on the R HV winding, etc. If it is truly reversed then the internal connections are such that polarity dots are on opposite ends of the winding and are 180 degrees apart, and your generatior and system will be rotating in opposite directions. You must test to know this for sure, fortunately it is not hard to do.

In answer to your protection question, regardless of what you do, none of the above will have any meaning unless you very carefully check and verify that the polarities of both sides of your PTs and CTs and their secondary wiring is 100% correct. Any error will result in the possibility of out of phase closure despite the synchroscope reading "correctly". Check, recheck, and check again, failure to do so results in damage that is both instantaneous and massive.

One more thing, you have not mentioned how your auxiliaries are connected. If you have any kind of automatic transfer switch and there is any rotation or phase shift differences then the transfer could be problematic even though the synchronization is successful.

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Bibo92004 (1); ijanto (2); Joshi (1); raghun (1); RAMConsult (1); Tornado (1)

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