Development of a High Efficiency Induction Motor:

With ever-increasing energy cost the life-time operating cost of an induction motor can be traded against a high efficiency and high capital cost induction motors. With rising demand for high efficiency or energy efficient induction motors, designers and manufacturers are stepping up their production of such motors.

Some of the important techniques, that are employed to construct a High Efficiency Induction Motors compared to the standard design, are listed below:

• Reduced current density in copper of stator winding resulting in reduced copper loss but increased copper weight and so cost.
• Reduced flux density in air-gap by increasing stator and rotor core length. This leads to reduced magnetic saturation and core loss.
• Larger stator steel volume improving heat transfer out of motor and so re­duced operating temperature. Rotor fans are designed with refined aerody­namic fin shapes to reduce windage loss.
• Use of high grade electrical steel with low hysteresis loss.
• Use of very high resistivity steel and very thin gauge laminations with conse­quent reduction in eddy-current loss.
• Rotor is fine, the machine to produce uniform air-gap, thereby reducing the stray load loss.

Achieving maximum efficiency needs both optimum design of the electric machinery and proper matching of machine and desired application.

Increasing the cross-sectional area of the windings would reduce the resistance and the I²R losses. For a given flux density eddy-current losses can be reduced by using thinner iron laminations.

There is a trade-off involved always. A machine of more efficient design normally requires more material and therefore is bigger and costlier. Users normally select the “lowest-cost” solution to a given requirement. Of course it would be prudent to choose an energy-efficient motor as normally the increased capital cost would be offset by energy savings over the expected lifetime of the machine.

To optimize the efficiency, it is important to select the smallest-rating induction motor which can adequately satisfy the requirements of a specific application. Use of modem solid-state control technology can also play a significant role in optimizing both performance and efficiency. In selecting a motor the main constraint is that the motors are normally manufactured in certain standard sizes. If 0.9 kW motor is needed one may end up buying a 1 kW motor. A custom-designed and manufactured 0.9 kW motor can be economically justified only if it is required in large number. There should not be, as far as possible, the mismatch of the motor to its application. For example, even the most efficient 100 kW motor will be somewhat inefficient when driving a 60 kW load.