3 phase transformer terminal connection 4

[sramesh]

Good day to you

The existing Transformer 33/6.6 kV Dyn 11 failed due to winding fault and we have got another spare transformer of 33/6.6kV Dyn11 with HV/LV terminal connection
C-B-A /c-b-a , where as original failed transformer had
U-V-W /u-v-W ( Please refer attached drawing).
To match the 6.6 KV bus duct, we propose to connect 33KV cable Red phase to HV terminal C, Yellow phase to B and Blue to C. With this Cable connection, will there be any effect on 1. Phase sequence in the secondary
2. Vector angle bewen primary and secondary.
3. Any other effect on running 6.6kV motors or to the electrical system

Your expert comments/ advice is appreciated.

thanks in advance

 

[slavag]

Hi.
Xmmm.
actually
A=U
B=V
C=W

In your old application R was connected to C ( swap red and blue connections on both side of the trafo), that means from Dyn11 trafo do Dyn1 trafo,
From my point of view you have provide same swap, that means , connect Red to W and Blue to U.

"To match the 6.6 KV bus duct, we propose to connect 33KV cable Red phase to HV terminal C, Yellow phase to B and Blue to C."
small mistake in your post, Blue to A.

Will wait to othert.
Good Luck.
Slava

 

[sramesh]

Thanks for quick reply and correction.

 

[Marmite]

Is the diagram correct? I would expect an old Brush transformer to be labelled ABC and a new ABB transformer to be labelled UVW, rather than the other way round.
If the diagram is correct then your old Brush transformer in the second diagram is connected standard ie R-U, Y-V, B-W which will give you a standard Dy11, whereas the new ABB transformer in the first diagram has A&C (R&B) crossed on both sides which will give you effectively a Dy1. The phase rotation will be the same as the old one, but the phase angle between primary and secondary is different, which will only have an effect if you parallel the LV side with any other existing mains derived sources downstream on your system.
Regards
Marmite

 

[sramesh]

Thanks and Phase angle change will not be a problem as we will not synchronise this Feeder. But another question is on Differential Relay, we have combined differential relay protecting the 33kv Cable (6KM) and the transformer winding, using GE MBCI with MCTH (inrush current block). Will the Vector change affect the functioning of the Differential relay

Regards
Ramesh

 

[Marmite]

Yes, it probably will affect the differential protection. Where exactly are the differential CT's located on the HV and LV sides?
The MBCI is a traditional non numeric pilot wire differential protection relay without the facility to programme software interposing CT's to compensate for the phase shift. The CT secondaries are connected to cancel out the effect of the phase shift of the transformer, so with a DY11 transformer, the CT's would be connected YD1. If you make the main transformer DY1 you will need to alter the delta CT secondary connection to correct the new phase shift.
Regards
Marmite

 

[sramesh]

Thank you very much for the reply,

The HV CTs are located in the 33kV feeder panel and LV CTs are locted in the 6.6 kV breaker panel.

Can you please explain on how to alter the delta CT secondary connection to correct the new phase shift.

Regards
ramesh

 

[slavag]

Hi Ramesh.
Please attach connection diagramm of secodary wiring to GE relays.
Are you have aux CT for the phase shift correction?
Best Regards.
Slava

 

[sramesh]

Dear Slavag / Marmite , Good day to you

Please find the attached document and proposed to change the CT wiring as suggested in the document. kindly go through and give your opinion on the correctness. Thanks in advance for your tecinput.

Kind Regards

Ramesh

 

[sramesh]

Dear All,

Thank you verymuch for your suggestions.
Motor started successfully and no Transformer differential trip,after Transformer Secondary side CT wiring changed as mentioned in my previous message.

Kind Regards

Ramesh

 

[slavag]

Hi Ramesh.
Im happy for you.
Thanks for the fedback.
Best Regards and Good Luck.
Slava