Electric Motor Basics (Rotor Movement)

Electric motor basics

Rotor movement

Reversing polarity with alternating current:
Magnetic polarity is continuously reversed by means of alternating current, (AC). Later, we will see how the rotating magnet is replaced by the rotor by means of induction. Alternating current is important in this regard, so a brief presentation should be useful:

Alternating current – AC:
By alternating current, we mean an electrical current that reverses in intervals and has alternating positive and negative values.

A rotating magnetic field can be created by using threephase
power. This means that the stator is connected to an AC source which supplies three separate current flows (also known as phases), all of them applied to the same circuit.

 A complete cycle is defined as having 360
degrees, which means that each phase is different from
the others by 120 electrical degrees. They are illustrated
in the form of sinus curves such as those presented to
the right.

The poles change:

On the following pages we will explain how the rotor and the stator interact and thus make the motor turn. In order to illustrate this clearly, we have replaced the rotor by a magnet that turns and the stator by a stationary part with coils. The illustration on your right-hand side, should be considered as a two-pole three-phase motor.
The phases are connected in pairs like in a real motor;
phase 1 consisting of A1 and A2, phase 2 consisting of
B1 and B2 and phase 3 consisting of C1 and C2. When
current is applied to the stator coils, one coil becomes a
north pole and the other becomes a south pole. So, if A1
is a north pole, A2 is a south pole. The principle we can
derive from this is that when the current is reversed, the
polarity of the poles is also reversed.