Now i'm making a rennovation of housing buildings, the existing voltage level is 127v 1ph, i'm planing to replace each duplex outlet 127v by single 120v+single 220v.
The dry-type transformer is 480/220v, so if we replace that transformer by 480/208/120, so we can derive 240v by collecting 120+120, would that work?
& what is the effect of 240v for the equipments?
If you are outside of North America, you will have electical distribution systems that are fundamentally different, and somewhat restricted, from those you will see in the discussions on this forum.
You need to have some understanding of electrical theory using vectorial math. You also need to be careful with your terms, there is a big difference between a 'phase conductor' and a 'phase voltage', so I try to use stick with terms like Line or Hot and Neutral when discussing conductors.
Most non-North American residential systems are 2-wire circuits derived from 3-phase 4-wire transformer connections. This is not true in the US where the majority of systems are 3-wire circuits derived from 3-wire transformer connections.
We also have different voltage levels which can really add confusion.
Our National Electric Code requires use to use the nominal voltages of 120V, 208V, 240V, 480V when describing electrical systems, however most of our utilization equipment has nameplates voltages which are less than system voltages, such as motors labeled as 230V. One result of this, is our tendency to round voltages up or down to the nominal US system voltages even when we are discussing non-North American systems. We also do not have a single method of 'writing down' our voltages, many try to follow ANSI recommendations, however many, if not most, of our utilities and electricians do not.
So:
In the US, we have common non-industrial voltages of:
120V 1-phase 2-wire
120/240V 1-phase 3-wire (the 120V comes from center-tapping the 240V)
120/208V 1-phase 3-wire (the 120V comes from the midpoint of a 208V wye, or star, connection)
240V 1-phase 2-wire
208Y/120V 3-phase 4-wire
240/120V 3-phase 4-wire (the 120V comes from center-tapping one 240V winding of a delta connection)
480Y/277V 3-phase 4-wire
In other parts of the world, it seems they only have:
127V 1-phase 2-wire (derived from the midpoint of a 220V star connection)
230V 1-phase 2-wire (although some areas, until recently, were 220V while others were 240V)
400Y/230 3-phase 4-wire.
What I am getting at is: be confident that we are discussing the same system. Simply using voltages levels as descriptors can definitely lead to the improper conclusions.
