To learn Engineering thinking in Electric Machine Course

It happens all the time. You arrive at your first class of the electric machine course on a bright sunny day with all your expectations to know those mysterious machines well for the rest of 16 weeks; you're full of energy and determinations and you can almost taste the feeling that you are now a real electrical engineer and fix those annoying problem with your car motor. And then I utter those dreaded words: let's first revise those electromagnetic induction laws learned in Physics.

Then you think I have given that knowledge back to my Physics teachers. All of sudden, all the brightness has gone. Especially when we are up to magnetic flux, the magnetic motive force, magnetic flux density, magnetic strength, we are overwhelmed by those words without really seeing them.

It is all those scientists' fault. Even though Henry Cavendish who firstly discovered electric ohm's law decided to not publish, his admirer James Clerk Maxwell a century later in 1879 helped him to publish it long after other scientists had been credited with the same results. Nobody would stop the development of science, technology and engineering.

In my opinion, all the pioneer scientists were dedicated to explaining those Physics phenomenon （they see the electromagnetic phenomena by using experiments） in such way that even without see it and touch it, we can analyze and apply them. Then obviously there is a big gap between phenomenon and abstract physics laws. I am just wondering whether the ability of spatial imagination might help. As a learner, our task is to fill in the gap with our imagination or so-called analysis skills.

Let's look at the magnetic flux and magnetic force, reluctance, magnetic flux density and magnetic strength. So many parameters are invented by scientists to explain just electromagnetic phenomena. It all started from the experiment that two magnets attract/oppose each other and then some mysterious force can move the wire carrying current.

The history is long but for now, what we can do is that to try to understand magnetic flux is something to quantity how big the magnetic effect in a certain area or cube. The experiment also shows that the higher electric current, the higher magnetic effect, which will give us a magnetic motive force which is equal to NI. Who cares what force really is, anyway everyone in the scientific world know it is proportional to current.

Then different material in the world shows different resistance or conductance to magnetic effect. Then magnetic B-H curve experiment is introduced to study it. Then permeability is introduced to represent the feature of different curve therefore different material. The method to develop the parameter "permeability" is still widely used nowadays for innovations of fundamental science. At the same time, the saturation phenomena were observed and explained further by the curve, which has a significant impact on the design and operation of an electric machine.

Lei Zhang, Ph.D. (lzhang@utec.edu.pe)

Energy Engineering Department