As I understand it, the supplies to domestic dwellings in USA, are derived from transformer secondary windings for the 220V, and with the centre grounded, for the 110V supply to lower power devices, e.g. fridges etc.
What is the transformer configuration, for say a pole mounted transformer to a dwelling, would this be 2 phase with centre grounded? and phase displacement of 120 degrees And what is the standard small industrial transformer setup at low voltage, is this a delta star transformer?
Single phase primary and secondary which has a grounded center tap. No phase displacement.
The vast majority of electricity in the US is delivered as single phase or three phase but some people incorrectly describe split single phase services as "two phase", when in fact such services are really still single phase power.
As far as domestic supplies are concerned, most residences receive 220- [240] volt single phase electricity with a grounded center-tapped neutral, the purpose being to limit voltage to ground to less than 150 volts from either "hot". This center tapped 220volt supply is sometimes mistakenly called "two phase". There may still be pockets of
2-phase power, meaning the simultaneous provision of sine wave and cosine wave electricity (that is, 90 degrees out of phase) [for industrial and commercial purposes] in Philadelphia/South Jersey but it is being phased out- [no joke intended] and somewhere out west...
Yes, although many Americans say "wye" instead of 'star'.
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