Y:Y transformer primary wiring - 4 or 5 wire?

[meternerd]

In the 21 years that I have been in the industry providing transformers to industrial/commercial customers I have never once was required to provide a Y-Y transformer. To the best of my knowledge it is common for utilities to use Y-Y transformers for transmission but for a service entrance D-Y are commonly used.
Is this a transformer that you are required to purchase and will be owned by you? How about the utility metering? I am assuming that there will be CTs amd PTs involved. Are they on the 13.8kv side which they probably are?

I agree with you to question the Y-Y transformer requirement.

I've been in the utility industry for 40 years. In my experience, it's just the opposite of your statement. Transmission is almost always Delta, since running 4 conductors is MUCH more expensive than running three. Once the transmission hits the substation, it is usually wired Delta Primary and Grounded Wye secondary. The 4 wire grounded Wye distribution system is then run to service transformers. Most modern systems (underground especially) are Wye/Wye. In the west, the most commn distribution voltage is 12,470/7200.


As mentioned, the primary neutral and secondary neutral of medium voltage transformers have a common H0 / X0 terminal that is externally bonded to the enclosure and ground. The neutral is connected to a grounding electrode. The bond to the common neutral is removable to allow megger testing.

 

[mbrooke]

I've been in the utility industry for 40 years. In my experience, it's just the opposite of your statement. Transmission is almost always Delta, since running 4 conductors is MUCH more expensive than running three. Once the transmission hits the substation, it is usually wired Delta Primary and Grounded Wye secondary. The 4 wire grounded Wye distribution system is then run to service transformers. Most modern systems (underground especially) are Wye/Wye. In the west, the most commn distribution voltage is 12,470/7200.


As mentioned, the primary neutral and secondary neutral of medium voltage transformers have a common H0 / X0 terminal that is externally bonded to the enclosure and ground. The neutral is connected to a grounding electrode. The bond to the common neutral is removable to allow megger testing.

It depends on where in the transmission system and what utility. Y-Y and D-Y are on average as a whole used about equally. Grounded wye auto is almost exclusively used from stepping 345 kv to 115kv, similar to 115kv down to 69kv. The distribution transformers in the substations lean more tward Delta wye, but wye-wye is seen to, such as the case where a 69kv line was reinsulated to 115kv and an ariel ground is present. The transformer reconfigured and reused in this case.

As for distribution wye-wye is almost exclusively used in the east while in California a good chunk of the lines are 3 wire and have loads conected Delta.

 

[mayanees]

OP here...thanks for all the comments.
My question's been answered, and that was - do I run an egc with my 3 concentric neutral phase conductorsz?. It's actually been answered by NYSEG who has dictated that it's a 4-wire primary for the customer-owned YG-YG transformers, just as described by meternerd.
John M