25.1.1 Induction Motor Operation The induction motor uses induced magnetism (magnetism generated by an electric current) to convert electrical energy into magnetic energy (a magnetic field). This magnetic field interacts with an existing magnetic field to cause mechanical energy (movement) in the form of a rotating rotor. As shown in Figure 25‑1, a cylinder (rotor) is rotated inside a magnetic field produced by an assembly of stationary electromagnets (stator). An electromagnet has two distinct advantages: • • Its core is magnetized only when current flows through the coil. When no current flows, there is no magnetic field. • • The polarity of an electromagnet can be changed by reversing the direction of the current flowing through the coil. Ordinary 60-cycle alternating current automatically reverses the north/south polarity of the stator poles 120 times per second. As shown in Figure 25‑2, two or more stationary electromagnets (poles) are positioned at opposite sides of a circle inside the motor. These stationary poles have opposite magnetic polarity. When the alternating current flow automatically N S N S Rotor Stator Stator windings Rotor A B Goodheart-Willcox Publisher Figure 25‑1. Main parts of an induction motor. A—A simplified end view of an induction motor, showing the magnetic poles of the stator and rotor. B—A motor’s rotor and the stator windings can be seen easily with the end bell of a semihermetic compressor removed. Power source S N N S Power source Magnetic polarity reversed 1 Cycle + - 1 Cycle - + South-North Polarity First Half of AC Cycle North-South Polarity Second Half of AC Cycle Goodheart-Willcox Publisher Figure 25‑2. Alternating current automatically reverses the polarity of the stator’s magnetic poles during each cycle. 486 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.