what is the standard 3-phase service transformer connection in the US?

[sliderule]

Here in Canada, a delta primary with 120/208 volt wye secondary is standard in commercial applications, then up from there, 347/600 volt wye secondaries (both with grounded neutrals. I thought in the US, a delta primary with 120/208 wye secondary is common and then 277/480 volts.

Some told me today "A DELTA transformer with mid-phase neutral tap is the norm in the USA. Down here four wire high voltage 3-phase transformers are the norm. Wye connected transformers." Not exactly sure what he is saying. Is he saying a wye primary with a mid-tap delta secondary is the norm for the US?

Thanks

 

[infinity]

Here in Canada, a delta primary with 120/208 volt wye secondary is standard in commercial applications, then up from there, 347/600 volt wye secondaries (both with grounded neutrals. I thought in the US, a delta primary with 120/208 wye secondary is common and then 277/480 volts.

Some told me today "A DELTA transformer with mid-phase neutral tap is the norm in the USA. Down here four wire high voltage 3-phase transformers are the norm. Wye connected transformers." Not exactly sure what he is saying. Is he saying a wye primary with a mid-tap delta secondary is the norm for the US?

Thanks

For commercial office buildings, many strip malls, malls, stores, etc.the standards would be 208Y/120 and 480Y/277.

 

[zbang]

Some told me today "A DELTA transformer with mid-phase neutral tap is the norm in the USA. Down here four wire high voltage 3-phase transformers are the norm. Wye connected transformers." Not exactly sure what he is saying. Is he saying a wye primary with a mid-tap delta secondary is the norm for the US?

Might be common in his area, but 'round here, virtually every commercial or industrial building newer 50-60 years and not served by MV has 3-phase 4-wire Y service at either 120/208v or 277/480v. I hardly ever even see 120/240v 3-phase with a high leg. Maybe I don't get out enough .

I understand that 120/240 high-leg delta services are more common in (semi)rural areas, as are open-delta 3-phase, but don't see those in most cities.

 

[Carultch]

Here in Canada, a delta primary with 120/208 volt wye secondary is standard in commercial applications, then up from there, 347/600 volt wye secondaries (both with grounded neutrals. I thought in the US, a delta primary with 120/208 wye secondary is common and then 277/480 volts.

Some told me today "A DELTA transformer with mid-phase neutral tap is the norm in the USA. Down here four wire high voltage 3-phase transformers are the norm. Wye connected transformers." Not exactly sure what he is saying. Is he saying a wye primary with a mid-tap delta secondary is the norm for the US?

Thanks

The WYE systems are a lot more common. The most common are split single phase 120/240, three phase 120/208, and three phase 277/480. Because it allows for the use of multiple voltages across loads from the same system of wiring, as well as the ability to balance the load currents.

And for the 277/480 systems, it is common that there is also a smaller 120/208 system on the premises for standard receptacles and other light duty loads.

DELTA systems, like the 120/240 high leg, have an advantage only when it is three-phase loads that dominate the service. Because there are few (if any) applications where the 208V to neutral high leg is even usable. And thus the B-to-C and A-to-B windings have a lot less current on them than the C-N-A winding. Because all the 120V loads have to be on the C-N-A winding.

 

[Jraef]

"Standard" as it applies to service transformers is anything but... That goes all the way back to the days of Tesla, Westinghouse and Edison. There was no concerted effort to create, let alone enforce, any kind of standardization of power transmission systems until the 1930s, but by then it was all over the map already.

By the way, I have seen PLENTY of 480V distribution systems, both Wye and Delta, at lumber mills and mines in Canada too, especially in BC and Alberta. There is no "standard" there either.

 

[sliderule]

I would agree with the 480V in industrial facilities in BC, but I assume the transformation to 480V would be the customer's equip. I was thinking more in terms of service voltages provided by a utility company to a commercial/institutional/light industrial customer and also in terms of current standards.

"Standard" as it applies to service transformers is anything but... That goes all the way back to the days of Tesla, Westinghouse and Edison. There was no concerted effort to create, let alone enforce, any kind of standardization of power transmission systems until the 1930s, but by then it was all over the map already.

By the way, I have seen PLENTY of 480V distribution systems, both Wye and Delta, at lumber mills and mines in Canada too, especially in BC and Alberta. There is no "standard" there either.