What Are The Different Type Of
Motors?
Squirrel Cage Induction Motors
The squirrel cage induction motor is
the most common type of large motor used in a thermal generating
plant. Squirrel cage induction motors are very rugged and require
very little maintenance.
Wound Rotor Induction Motors
The wound rotor induction motor has a
rotor winding which is brought out of the motor through slip rings
and brushes. While more flexible than a squire cage induction motor,
the slip rings and brushes are an additional maintenance item. Wound
rotor motors are only used in special applications in a power plant.
Synchronous Motors
Synchronous motors may be required in
some applications. Large slow-speed, 1800 rpm or less may require a
synchronous motor. A synchronous motor may used to supply VARs and
improve voltage regulation. If the synchronous motor is going to be
used as a VAR source, the field supply must be sized large enough to
over-excite the field.
Direct Current Motors
Direct current motors are used
primarily on emergency systems such as turbine lube oil and turbine
turning gear. Direct current motors may also be used on some control
valves.
Single-Phase Motors
Single-phase motors are fractional
horsepower motors and are usually supplied with the equipment.
Motor Starting Limitations
The starting current for induction
motors is about 6 times full load current. This must be taken into
account when sizing transformers and should be part of the load flow
analysis.
If the terminal voltage is allowed to
drop too low, below 80%, the motor will stall. Methods of reduced
voltage starting are available, but should be avoided if possible.
The most reliable designs are the simplest.
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