3-Phase Help

[Jamie Medeiros]

Does anyone know if a motor wired for 208 y three phase can be run using 240 delta three phase?

[ThomD]

I always check with these guys:

Transformers, Phase Converters and VFD

[Mark Kelly]

Short answer: no, the voltages are wrong.

Here's an easy way to visualise this: draw an equilateral triangle point up. Draw in the centre point (1/3 of bisector). Connect each vertex to the centre point. The lengths of the sides are the delta voltages, the lengths of the centre arms are the wye voltages. Since the arms are 2/3 of the bisector and the bisector is 2/SQRT3 of the length of the sides, the ratio of the two is SQRT3.

208 x SQRT3 = 360.

Longer answer: are you sure about the voltages you quote? Usually 208V is the phase to phase voltage giving 120V phase to neutral. 240V phase to phase is therefore about 20% higher

[suicideking]

Short answer: no, the voltages are wrong.

Here's an easy way to visualise this: draw an equilateral triangle point up. Draw in the centre point (1/3 of bisector). Connect each vertex to the centre point. The lengths of the sides are the delta voltages, the lengths of the centre arms are the wye voltages. Since the arms are 2/3 of the bisector and the bisector is 2/SQRT3 of the length of the sides, the ratio of the two is SQRT3.

208 x SQRT3 = 360.

Longer answer: are you sure about the voltages you quote? Usually 208V is the phase to phase voltage giving 120V phase to neutral. 240V phase to phase is therefore about 20% higher

This might be the most informed and best worded reply i have ever read on this site. Bravo sir! Bravo!

[Rosko]

Does anyone know if a motor wired for 208 y three phase can be run using 240 delta three phase?

James,
you could wire up a VFD to convert* the 208(?) wye to 240 delta.

*(perhaps mimic is a better word)

I've done some similar set-ups. Feel free to shoot me an email or call if need be.

[Mark Kelly]

This might be the most informed and best worded reply i have ever read on this site. Bravo sir! Bravo!

Thanks but it's also wrong. I meant to say "Since the arms are 2/3 of the bisector and the bisector is SQRT3/2 of the length of the sides, the ratio of the two is SQRT3".