Premium Membership ♕

Save 50% on all Video Courses with Enterprise Membership Plan and study specialized LV/MV/HV technical articles and guides.

Operating Characteristics Of Motor


The effective or useful power output supplied by the motor at the shaft end is lower than the power input absorbed by the motor from the power supply, i. e., the motor efficiency is always below 100%.

Guide To Specification of Electric Motors by WEG
Guide To Specification of Electric Motors by WEG (photo credit:

The difference between input and output represents the losses that are transformed into heat. This heat warms up the windings and therefore must be removed from the motor to avoid excessive temperature rise. This heat removal must be ensured for all types of motors.

In the automobile engine, for example, the heat generated by internal losses has to be removed from the engine block by water flow through radiator or by fan, in the case of air-cooled engines.

Heat dissipation

The heat generated by internal losses is dissipated to the ambient air through the external surface of the frame. In totally enclosed motors this dissipation is usually aided by a shaft mounted fan.

Good heat dissipation depends on:

  1. Efficiency of the ventilating system;
  2. Total heat dissipation area of the frame;
  3. Temperature difference between the external surface of the frame and the ambient air (text-ta).

A well designed ventilation system, as well as having an efficient fan capable of driving a large volume of air, must direct this air over the entire circumference of the frame to achieve the required heat exchange. A large volume of air is absolutely useless if it is allowed to spread out without dissipating the heat from the motor. The dissipation area must be as large as possible.

However, a motor with a very large frame require a very large cooling area and consequently will become too expensive, too heavy, and requires too much space for installation.

To obtain the largest possible area while at the same time keeping the size and weight to a minimum ( an economic requirement ), cooling fins are cast around the frame.
Internal drop in temperature
Internal drop in temperature

An efficient cooling system is one that is capable of dissipating the largest possible amount of heat through the smallest dissipation area. Therefore, it is necessary that the internal drop in temperature, shown in figure above, is minimized.

This means that a good heat transfer must take place from the inside to the outer surface of the motor.

Title:Guide To Specification of Electric Motors – WEG
Size:12.1 MB
Download:Right here | Video Courses | Membership | Download Updates
Guide To Specification of Electric Motors
Guide To Specification of Electric Motors

Premium Membership

Get access to premium HV/MV/LV technical articles, advanced electrical engineering guides, papers, and much more! It will help you to shape up your technical skills in your everyday life as an electrical engineer.
50% Discount 💥 - Save 50% on all 90+ video courses with Enterprise Membership plan.

More Information


  1. José Aular
    Jun 17, 2020

    Thanks for your big work. It’s very important.

  2. hesham
    Dec 01, 2016

    thanks for your wonderful work

  3. youssef
    Nov 29, 2015

    the heat problem is solved for superconductor motor

  4. Ravi
    Dec 23, 2014


  5. Ravi
    Dec 23, 2014

    its very useful refresher for us engineers

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

five  +    =  eight

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge