| Don Kelly 2008-03-27, 3:25 am |
| ----------------------------
"VIDHYA" <vidhya36@gmail.com> wrote in message
news:91ad3917-1444-4d71-bb6e-27bbeb298206@s13g2000prd.googlegroups.com...
> both 3phase induction motor and transformer are working on the same
> principle of em induction only , in motor alone why rmf is produced
> why not in transformer?
First of all "rmf" is ???. I am not familiar with the term but one
reference indicates that it is "rotating magnetic field". If so, then the
reason is that , in the induction motor the physical design is such that a
rotating field is deliberately produced- done by spatial separation of the
phases around the stator. This is not done in a polyphase transformer (while
the flux distribution shifts periodically it doesn't "rotate") -an
exception being a polyphase induction motor at standstill.
Secondly there is more to d/dt(Li) than simply Ldi/dt which is a
"transformer voltage"
There is also a term (i)(dL/dt)w where w is the angular velocity- this is a
"speed voltage" which is generally larger than the transformer voltage- in
any motor, AC or DC, and is the voltage of concern in considering power
transfer and is often called the back emf.
Does this help?
--
Don Kelly dhky@shawcross.ca
remove the X to answer
|