Why does changing two leads change the rotation of a 3 phase motor

[Eagle20]

Why does switching two leads on a 3 phase motor change the rotation?

 

[Kiljoy]

Because each lead is 120 degrees out of phase, you create a rotating magnetic field in the motor. Swap two leads and the field rotates in the other direction. That's why certain single phase motors require start capacitors to "simulate" another phase.

 

[rbulsara]

It reverses the phase sequence resulting in sequence of rotational forces applied. A<B<C changes to A<C<B, for example. The source sequence remains unchanged.

You may understand it better if you draw a wheel and note three points on its circumference 120 deg apart. Name them A, B and C. Imagine it being rotated by three forces A to B, B to C and C to A. If you interchange any two points of application, you will see the direction of wheel's rotation will reverse.

Rafiq Bulsara

http://www.srengineersct.com

 

[Eagle20]

Thanks fellas. I'm sitting in a vfd siminar and the instructor couldn't answer.

 

[rbulsara]

...resulting in reversal of...

Rafiq Bulsara

http://www.srengineersct.com

 

[jraef]

Sad that "VFD seminar" instructor can't answer that question...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[Eagle20]

He couldn't answer anything. Very bad instructor and waste of money

 

[Eagle20]

He couldn't answer anything. Very bad instructor and waste of money

 

[waross]

He probably sells a lot of VFDs to people to whom that question would never occur.

Bill
--------------------
"Why not the best?"
Jimmy Carter