Electric Motor Control Basics - Book - Page 20
Industrial Control Basics: Part 2, Overload Relays
Squirrel Cage Induction Motors
Induction motors equipped with a squirrel cage rotor are known as squirrel cage
induction motors. They get their name because the rotor resembles the rotating
cylindrical “cage” that you might find in a pet squirrel or hamster cage. These motors
are available in sizes ranging from fractional horsepower (HP) less than one kilowatt to
10,000’s HP (tens of megawatts). Factors such as simplicity, rugged construction, and
constant speed in different load sizes have contributed to their popularity. Like other
induction motors, the squirrel cage motor consists of:
• Rotor: It is a cylindrical-shaped component mounted on a shaft. It contains
longitudinally organized conductive bars. The bars are made of copper or
aluminum, and are set into grooves, which are connected at ends to form a cagelike structure. The rotor has a laminated core, which helps avoid power loss due
to hysteresis and Eddy currents. Conductors of the rotor are skewed, which
helps prevent cogging during the start of the equipment. Also, this skewing assures
improved transformation ratio between the rotor and stator.
• Stator: It consists of a three-phase winding along the core. The stator is placed
in a metal housing. The windings in the stator are organized such that they are
120-degree apart in space, and mounted on a laminated iron core. This iron core
provides reluctance path for flux generated by AC currents.
Industrial Control
Basics:
Part 1, Contactors
Industrial Control
Basics: Part 2,
Overload Relays
Industrial Control
Basics: Part 3,
Starters
The Benefits of Type E/F
Motor Protection
Circuit Breakers
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
Application
NEMA vs IEC Motor
Controls
Understanding
IP Ratings
20
