Routing/Connection of Transformer neutral conductor

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PJB1971

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I'm connecting a 3 phase 208/4160V (Y-Y) transformer (1500 kva) for which the Y is grounded on the primary and secondary. The secondary connection connects at a bus breaker. The primary is fed from a switched/fused source (utility). Is it a requirement to run the neutral conductor of the transformer with the phase conductors where the neutral connection will be made at the switch?
 
It is unclear which neutral you are asking about, but the neutral on each side of the transformer must be run with the phase conductors. Why depends on which neutral you are asking about.

Can you give more information?

Jim T
 
The utility is a 3 wire 208V source (Fused Switch) which is feeding the 208V Y side of the 208?4160V 3 ph transformer. The existing connection is a 3 phase 3 wire 208V bus. The old transformer being replaced was a delta-Wye (208/4160V) and the replacement is a Y-Y (208/4160V) with the neutral of the Y grounded. Routing the neutral with the phase conductors is only possible if attached to the outside of the bus enclosure.

Any insights would be appreciated.
 
Just treat the new transformer like it is a delta on the 208 volt side. Don't make a neutral connection on the 208 volt side.
Routing the neutral with the phase conductors is only possible if attached to the outside of the bus enclosure.
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That would be a violation of 300.3(B).

Don
 
I disagree with Don. If you don't have a neutral on the high (208) side, you will have problems with a Y Y transformer connection. My old Westinghouse Distribution Transformer Manual has a cautionary note saying that if the primary neutral is not tied to the system neutral, excessive votlages may develop on the secondary side.

An ungrounded Y high side is very unusual. It is almost grounded Y or delta.

Jim T
 
Jim,
If you don't have a neutral on the high (208) side, you will have problems with a Y Y transformer connection. My old Westinghouse Distribution Transformer Manual has a cautionary note saying that if the primary neutral is not tied to the system neutral, excessive votlages may develop on the secondary side.
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Thanks...I was not aware of that.
Don
 
don_resqcapt19 said:
Jim,

Thanks...I was not aware of that.
Don
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Both Westinghouse and GE published small paperback books on transformer connections. They have a wealth of information. They were widely distributed to utility engineers in the 1960's, I don't know if they are still available.

I refer to them often.

Jim T
 
The utility will not take an outage to change the suppy to the building since the whole (supposedly) area will be blacl. The feed is an alternate feed to supply various gear when the plant goes down, The number of times this will be used is minimimal at best. Additionally the step from 208V to 4160V will be converted to 480 with existing 4160/480V transformer and switchgear. No 4160V loads will be energized. This is a means to provide lighting and small load power until backfeeding can be established thru the Swyd.
 
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