Ac Pm Motr

what is an ac pm motor? Is it a synchronous motor or induction motor? does it run at constant speed at a given frequency or has a slip?what is its construction like? what are its operating principles?
What are its advantages over conventional ac motors?
I understand these motors are increasingly becomming popular even in higher kw ratings

Double Cage Motors And Vfd Drive

I am somewhat mixed up with use of VFD drives in case of double cage motors.

1. In case of some VFDs we are required to feed equivalent circuit parameters of the motor.
In case of a double cage motor rotor resistance and reactance are different at starting and
running. These values are usually given at slip =1 and at slip =0.
The question is which values to feed?
To my mind it appears that because with VFD, slip =1 condition is not encountered we should
consider values at slip =0. Am I correct?

2. A double cage motor is used to have high rotor resistance at start and low rotor resistance at
running.This incidentally gives more rotor reactance at running than at start giving some what
lower power factor. When we use VFD, slip =1 is never encountered as frequency is adjusted as
per speed. So why to go in for a double cage motor for VFD drives ? It may unnecessarily
reduce power factor of motor. Is my analysis on right track?

Vfd Motor Failures

Are high slip motors more prone to insulation failures than normal slip motors (design
when operated from a VFD ?

In Rush Current And Starting Current

What is the difference between inrush current and starting current of an Induction motor?
What is the relation between them ?
Some manufacturers offer motors with low in rush current.In actual terms they or offering double cage motors or rotors with narrow slots which has lower starting currents.Does these motors have low switching currents?
It appears they are using terms starting current and inrush current synonymously.
Are they justified?

Copper Rotor Motors

I read lot of articles praising copper rotors instead of conventional aluminum rotors.
It is claimed that as conductivity of copper is more it has less resistance and low slip,lower rotor losses ans improved efficiency.
My problem is that in order to have a good starting characteristics we need to have
a definite rotor resistance.The choice is a compromise between lower losses and starting torque. This choice is without regard to material copper or aluminum.
So How does copper rotor helps to reduce losses at the same time maintaining
the required starting torque?
subrao