Induction motor is the most widely used type of e-motor. An induction motor like any other rotating machine consists of a stator (the fixed part) and a rotor (the moving part) separated by air gap. The stator contains electrical windings housed in axial slots. Each phase on the stator has distributed winding, consisting of several coils distributed in a number of slots. The distributed winding results in magnetomotive forces (MMF) due to the current in the winding with a stepped waveform similar to a sine wave. In three-phase machine the three windings have spatial displacement of 120 degrees between them.
For vehicle applications, recent developments in low-cost inverters have made variable-speed operation possible for traction drives.
There are few recent improvements to the AC motor for vehicle applications.
One of these is the use of a copper rotor instead of aluminum. Depending upon the size of the motor, the use of copper can increase the efficiency of an AC induction motor by one to three percentage points. Although this may seem like a small increase, it is significant in reducing the losses generated by the motor, easing thermal management. Depending on the vehicle, this could also add some distance to all-electric driving range as well.
Squirrel-cage motor is very simple and it is almost unbreakable. Its cost is low; it is highly reliable and rugged. It has very high efficiency, but main drawback is that induction motor is susceptible to different types of faults. Present-day situations demand rotor of electrical machine to be lighter in weight and faster in speed but tighter in tolerances and for these reasons, rotating machinery is becoming increasingly complex. With this increase in complexity, it is important to eliminate as many sources of faults as possible.
Induction motor performance may be affected by the following type of faults:
(a) Electrical-related faults
(b) Mechanical-related faults
(c) Environmental-related faults.
Main faults in induction motors may be listed as follows—(1) broken bar fault,
(2) bearing fault, (3) rotor mass unbalance fault, (4) bowed rotor fault, (5) stator
winding fault, (6) rotor winding fault, (7) single phasing fault, and (8) crawling.