MV wye/wye transformers

Status
Not open for further replies.
A

Alex-Electric

Member
Location
Fairfax, Virginia
Occupation
Electrician Journyman
We are required to supply 22.9KV delta - 480GRY/277V transformer for a student-housing project in FL; due to material shortage the manufacturer is offering a 13.2KV delta primary transformer reconnected to 22.8KV wye primary. We asked about the X0 connection on the primary side, they said that should be floated and not grounded.
Please advise if this is safe and acceptable or not.
 
I believe a grounded H0 on the primary would be appropriate in your case. It would stabilize the L-N voltages on the secondary when there are unbalanced L-N loads. And the outer 2 legs of the 5-leg core will provide a return path for a limited amount zero sequence flux due to unbalanced voltages on the primary (instead of having to go through the walls of the tank as with a 3-leg core).
I think a grounded-wye primary should also be less susceptible to ferroresonance when there is substantial capacitance on longer runs of underground feeders.
 
Thank you for the response, so the concern with the grounded WYE primary would allow fault currently on the secondary side to travel to the primary side, is that not the case?
Also the grounded WYE primary would make the transformer not separately derived system.
 
Status
Not open for further replies.
Top