Question on Grounding Transformer

[pwrtran]

How does it affect the system by adding a grounding transformer to a 4-wire ground wye system?
Please see the attached sketch.

Thanks!

 

[davidbeach]

Presumably the grounding transformer lowers the zero sequence source impedance and the fault current goes up. Depends on lots of factors though.

 

[pwrtran]

Case 2 is one of the configuration of DG connection set out by a transmitter in their technical requirement. The proposed DG is on Source 1 side with the grounding transformer. I don't understand these configuration on a both ends 4-wire grounded wye system.

Say Source 2 is a stronger source and the fault close to Source 1. If the grounding transformer is to reduce the DG's Zo, then fault contributed from DG will be higher than the case without the grounding transformer, in turn, it will de-sensitizing the relay at the Source 2, which is the station feeder.

 

[odlanor]

-case 2
1- zigzag phase terminals are ABC not BCN. Correct.
2- Jumping between zigzag and neutral establish a system solidly grounded:- Zigzag is not effective.

 

[pwrtran]

odlanor - you are right, it's my drafting error. Please see the corrected sketch with some description changes to provide some additional information.
Thanks

 

[odlanor]

-case 2
Jumping between zigzag and neutral establish a system solidly grounded:- Zigzag is not effective.
To reduce current contribution of left wye-grounded to L-G fault, you have to desconnect zigzag from neutral , and calculate zigzag for 3 < X0/X1 < 10.

 

[odlanor]

i am sorry for 2nd row:

-case 2Jumping between zigzag and neutral establish a system solidly grounded:- Zigzag is not effective.To reduce current contribution of left wye-grounded to L-G fault, you have to unground neutral, disconnect zigzag from neutral ,ground zigzag, and calculate zigzag for 3 < X0/X1 < 10.

 

[jghrist]

What is DG?

What kind of relay at Station 2 do you consider that would be desensitized by the addition of a grounding transformer?

 

[pwrtran]

jghrist

DG-Distributed Generation. It could be rotation machine type or solar panels.

The generator is responsible for having a consulting company doing the design. As an utility we look after the CIA (Connection Impact Assessment) to our distribution system and the station before their detail design. If the portion the line is embedded to another utility, say the transmitter, or the station is owned by the transmitter then we need to meet their technical requirement. That is where my posted question came from.

The transmitter company has so many department and so many people and I find myself frustrated to get touch base with the correct person who can hit the technical question right on the nail.

 

[odlanor]

pwrtran
Could be this configuration?:
DG are installed in source 1 at low voltage side of wye-ungrounded /wye-grounded. Generators are ungrounded . A bus generation with zigzag, will connect wye-ungrounded side and all generators.