Induction Motor Design

Hello, fellows, I hope all of you are having fun in your life. In today’s tutorial, we will have a look at induction motor design. In 1880, Nikola Tesla (who was an American engineer) gave the basic principles of the induction motor; in 1888, due to his ideas on the induction motor, he received a patent. He offered the paper to the American Institute of Electrical Engineers, in which he explained the working principle of the wound-rotor induction motor. He also explained the working principles of the synchronous motor and reluctance motor.

Though the elementary knowledge of the induction motor was defined in 1888, the motor itself did not spring forth in the complete arrangement. There was an early era of fast progress, followed by a sequence of sluggish, evolutionary developments that have continued to this day. So let’s get started with induction motor design.

Table of Contents

The induction motor was presumed a familiar, up-to-date form between 1888 and 1895.
During this time interval, 2 and 3-phase energy sources (supplies) were invented to generate a revolving magnetic field in the motor.
With the two and three phases, there were also invented distributed winding and cage rotor design rotors for the motor.
In 1896 completely constructed 3-phase induction motors were available on the market for commercial use.

After 1896 and till the starting days of 1970, the best quality steel was introduced to the market, with which different casting methods, insulating materials, and different construction specifications of induction motors were developed.
By using these new parameters, such motors were developed so that cost-effective, smaller-size motors that produced desired output power were introduced to the world.
Today’s hundred-horsepower motor has a similar construction to the 7.5-horsepower motor that was used in 1897.
This development is demonstrated for fifteen-horsepower motors in the given figure.

See also this figure that shows the two thousand horsepower motor that used in previous years.

Though these developments in induction motor designing did not essentially lead to enhancements in motor functioning efficiency.
The main design change was leading to decreasing the original materials price of the motors, not to enhancing their efficiency.
The design effort was oriented in that direction as the price of electrical energy was higher, making the up-front price of a motor the main standard used by buyers in their choice.
Meanwhile, the expense of oil began its remarkable rise in 1973; the lifetime functioning price of motors has become very important, and the fitting cost has become comparatively less significant.

As a consequence of these parameters, new stress has been placed on motor efficiency both by engineers and by consumers of the motors.

How to Improve the Efficiency of an Induction Motor

There are some methods used to increase the efficiency of the induction motor.

A larger number of turns should be used in the stator for the reduction of the copper or I²R losses.
The reduction of the losses at the core increases the length of the stator and rotor cores; it will reduce the flux losses in the air gap of the motor.
A large amount of stator is used in the stating part (stator) of the motor; it will help to remove heat produced in the motor, and due to heat removal, the motor temperature will not increase. For the reduction of the windage losses, the motor fan is connected to the rotor.
The steel of the stator should be high quality so it can easily magnetize and demagnetize; in this way there will be fewer hysteresis losses.
The steel is prepared on a particularly thin scale, which means the laminations are very close to each other, and the steel provides larger inner resistivity. These properties decrease the eddy current losses in the motor.
The rotor is wisely designed to make a constant air gap; it will decrease the stray losses of the motor.

With these abovementioned methods, every manufacturing company has its own methods for the increment of the efficiency of the motor.
A distinctive higher efficiency induction motor is shown in the figure.

To help in the relationship of motor efficiencies, NEMA (National Electrical Manufacturers Association) has implemented standard methods for determining motor efficiency based on technique B of the IEEE (Institute of Electrical and Electronics Engineers) Standard 112, Test Process for Poly-phase Induction Motors and Generators.
NEMA (National Electrical Manufacturers Association) has also presented a rating known as NEMA nominal efficiency, that mentioned on the nameplates of design classes A, B, and C motors.
The nominal efficiency defines the average efficiency of a larger no of motors of a specified model, and it also assures a specific lowest efficiency for that kind of motor.
The given diagram shows the standard NEMA (National Electrical Manufacturers Association) nominal efficiencies.
Other standards groups have also recognized efficiency parameters for induction motors; the significant ones are the British (BS-269), IEC (IEC 34-2), and Japanese (JEC-37) standards.
However, the methods approved for determining induction motor efficiency are dissimilar in every standard and give different outcomes for a similar physical structure motor.

If 2 motors have 82.5 % efficiency, but they are defined according to dissimilar standards, then they cannot be correspondingly proficient.
When 2 motors are compared, it is vital to relate efficiencies found according to a similar standard.

It is the complete article on the Induction Motor Design if you have any questions about it ask in the comments. Take care until the next tutorial, starting method of induction motor.

You can also read some related articles to the induction motor. That is described here.