Synchronizing generators through stepup transformer 8

[Mark Lam]

Hi Guys!
we are doing synchronizing 02 gensets. one is 400v, the other one is 6.3kv genset. we use a step up transformer 400/6.3KV/DY11 to step up the voltage to 6.3kv and doing the synchronizng at 6.3kv side. Attached is single line diagram. The synchronizing controller is easygen 2300. when the controller close the 6.3kv breaker to syn. the 400v breaker at 400v side tripped immediatly.
so, i am thinking about the fault can come from the transformer with the questions as below:
1. The Step up transformer 0.4/6.3kv/DY11 is ok for this application?
2. the phase angle shift between primary winding and secondary winding of the transformer affected to the system when synchronizing?
3. the winding connection of the transformer need to match the winding connection of the gensets (both LV and MV side)?
Can you please give me advices for this case?
Thank you in advanced.

 

[che12345]

@ Mr. Palletjack (Electrical)17 Jun 22 14:04
"... Consider a Yy 0 transformer. When the HV Aphase is at the peck, the LV Aphase is also at the peck i.e. in synchronism. Now consider a Yy 11 transformer. When the HV Aphase is at the peck, the LV Aphase had .....Actually, depending on you HV configuration, the LV peak could be before the HV peak....".
Yes. You are right to say that "...LV peak could be before the HV peak...".
Mr. Mark Lam stated that the step up transformer is 0.4/6.3kv/DY11. I had in my earlier post mentioned that the standard notation is, cupper case letter denotes the HV and lower case for LV. Mr. Mark Lam has not advised the "revised"/clarified with the correct notation. I had made the presumption, for illustration purposes.
Che Kuan Yau (Singapore)

 

[che12345]

@ Mr. edison123 (Electrical)17 Jun 22 03:04
"...che ....By your 'theory', the only possible transformer connections for paralleling are y/Y and d/D with the same phase shifts, which is not the case in real life. So, wrong theory... "..
1. Disagreed. For syn, the basic requirements are equal voltage, frequency, phase sequence and phase angle (i.e. two voltage curves shall coincide). A Dy 11 or Yd 11 would NOT fulfill this basic theorem.
2. Yes, in the real life you see transformer with phase displacement and yet they syn.
3. When the step up transformer vector group can NOT be altered/must retain in Dy 11 or Yd 11 ; is it is possible to add a very low cost/simple (auxiliary transformer 1:1 or 1: 1.732 ratio say 100VA) after the HV PT , to shifts back the phase displacement. This is no rocket science.
Che Kuan Yau (Singapore)

 

[bacon4life]

@Che
What exact problem are you suggesting will occur by having transformers with different vector groups? The basic requirement for synchronization of having identical phase angles applies at the breaker where the synchronization takes place, not at the generator terminals. The OP stated that the 6.3 kV PTs are being used for synchronization, so I do not see any relevance any measurements coming from the 400 V PTs.

Within any large power grid, I suspect it would be easy to find examples of generators operating at all 12 possible phase shifts when comparing 500 kV grid phase A voltage to the generator terminal phase A voltage.

 

[edison123]

che

Google Synchroscope, it's not rocket science.

Muthu

http://www.edison.co.in

 

[che12345]

@ Dear Mr. edison123 (Electrical)18 Jun 22 02:12
"...che...Google Synchroscope, it's not rocket science...".
1. If you Google " Synchroscope " the rotating pointer type; there are two different Fast/Slow direction markings. Some marked (Fast) in the [CW rotation]. The other marked (Fast) in the [CCW rotation]. Both types are on the market, co-existing.
2. It don't matter which type is in use. The important thing is to understand that Fast indicates that the Gen speed/frequency is faster than the busbar. Hope this clarifies CCW or CW rotation which is dependent on the type/manufacturer.
3. In actual application, the Gen is ran up and adjusted slightly faster speed/higher frequency than the busbar. The synscope pointer is rotating in the Fast direction.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr. Mark Lam
In addition to my earlier post dated 17 June 22, I would like to add the following information which I felt essential, for your consideration.
1. Take note that (different synscope manufacturers) design their products with [different Fast/Slow CW/CCW rotational direction and terminal connection marking].
2. Strictly follow the meter label/manufacturer connection diagram. Take special attention to:
a) the terminal for " Gen" = incoming and " busbar" = network running. Some name them with differently terms,
b) the polarity (e.g. Gen L to terminal 1 , N to terminal 2. Busbar L to terminal 5 , N to terminal 6 ),
c) the phasing (e.g. Gen from Aphse-Bphase but Busbar from Bphasr-Cphase )
Che Kuan Yau (Singapore)

 

[Palletjack]

15
@ Mr. Palletjack (Electrical)17 Jun 22 14:04
"... Consider a Yy 0 transformer. When the HV Aphase is at the peck, the LV Aphase is also at the peck i.e. in synchronism. Now consider a Yy 11 transformer. When the HV Aphase is at the peck, the LV Aphase had .....Actually, depending on you HV configuration, the LV peak could be before the HV peak....".
Yes. You are right to say that "...LV peak could be before the HV peak...".
Mr. Mark Lam stated that the step up transformer is 0.4/6.3kv/DY11. I had in my earlier post mentioned that the standard notation is, cupper case letter denotes the HV and lower case for LV. Mr. Mark Lam has not advised the "revised"/clarified with the correct notation. I had made the presumption, for illustration purposes.
Che Kuan Yau (Singapore)

What I meant in my post was that for a Dy11 the LV could LEAD OR LAG the HV depending on the abc sequence connected to the HV terminals.
It doesn’t always lag the HV 30 degrees.
It’s the reason some systems have a 60 degree displacement.

 

[edison123]

che

and?...

Synchroscope measures and shows not only the frequency difference (by rotation) but also the phase angle (by position) between the power systems at the synchronizing point. And it is usually a single phase input device. So transformer vector groups don't matter for paralleling to the bus as evidenced in real world.

Hence, your theory " Yd 11 is NOT ok. Should be a Yy 0 or a Dd 0, of the same vector group" and "A Dy 11 or Yd 11 would NOT fulfill this basic theorem" is plain wrong. I am done.

Muthu

http://www.edison.co.in