The Complete Handbook of Electrical Motors

Chapter 1: Understanding Electrical Motors

An electrical motor is a machine that converts electrical energy into mechanical energy, specifically into rotational force, or torque, at a given speed. You are surrounded by them. The compressor in your refrigerator, the pump circulating water in a commercial boiler, the conveyor belt moving parts down an assembly line, and the spindle turning a CNC mill are all driven by motors. Understanding what happens inside that metal or plastic casing when you flip a switch is not an academic exercise. It is the foundation for correctly specifying a replacement part, diagnosing a mysterious failure, and predicting energy consumption that can amount to thousands of dollars a year.

The core principle behind nearly every electrical motor is electromagnetic induction, first discovered by Michael Faraday in 1831. Faraday showed that a changing magnetic field can cause electrons to move in a conductor. In a motor, we create that changing magnetic field using coils of wire, often called windings. These windings are usually housed in a stationary part of the motor called the stator. When alternating current (AC) flows through the stator windings, it produces a rotating magnetic field that spins around the inside of the motor. Inside this spinning field sits the rotor, the rotating component. The rotor is designed to react to that spinning magnetic field, and it is this reaction that produces the physical rotation on the output shaft.

While induction motors dominate the industrial world, it helps to understand a simpler