Three Phase Transformer Wiring and Connections

Delta and wye, the whole idea

In a delta connection the three windings are joined end to end in a closed triangle, and there is no neutral point. In a wye connection one end of each winding meets at a common point, which becomes the neutral. Wye gives you a neutral and therefore two useful voltages, phase to phase and phase to neutral. Delta gives you one, and is more tolerant of unbalanced load.

What L1, L2 and L3 mean

Simply the three energised conductors, the three phases. Naming them L1, L2 and L3 rather than A, B and C is a regional habit and nothing more. What matters is that their order determines rotation, and rotation determines which way a motor turns. Swap any two and the motor reverses.

The four combinations you meet

Delta to wye is the most common on distribution, because it feeds a four wire secondary and traps harmonics in the delta. Wye to wye is used where both sides need a neutral, but it needs careful grounding or it misbehaves. Delta to delta appears in industrial work with no neutral requirement. Wye to delta is used for stepping up. Our pad mounted units are normally delta primary to grounded wye secondary.

Is 480 volt three phase delta or wye

Usually wye, written 480Y/277, which gives 277 volts phase to neutral for lighting and 480 volts phase to phase for equipment. 480 volt delta exists in older industrial plants and has no neutral. If you see 277 anywhere on the nameplate or the panel schedule, it is wye.

What is the difference between a 480 volt delta transformer and a 480 volt wye transformer

Wye has a neutral point, so it gives 277 volts phase to neutral as well as 480 phase to phase, and is written 480Y/277. Delta has no neutral and gives only 480 volts phase to phase. Wye is the modern standard because the 277 volts feeds lighting directly.

Is 480 volt three phase wye or delta

Almost always wye in modern installations, shown as 480Y/277. Delta at 480 volts still exists in older industrial plants. If the panel schedule mentions 277 volts, the system is wye.

What is the most common connection for a three phase distribution transformer

Delta primary to grounded wye secondary. It provides the four wire secondary that buildings need and keeps triplen harmonics circulating in the delta winding rather than passing through to the system.

How do you know if a transformer is delta or wye

Read the nameplate. It states the connection for both windings, usually with a small diagram. A secondary written as 480Y/277 or 208Y/120 is wye. A secondary written as a single voltage such as 480 with no second figure is delta.