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AC Motors
AC Motors - Variable torque:
AC motors have a speed torque characteristic that varies as the
square of the speed. For example, an 1,800/900-rpm electrical motor
that develops 10 hp at 1,800 rpm produces 2.5 hp at 900 rpm. Since
ac motors face loads, such as centrifugal pumps, fans, and blowers,
have a torque requirement that varies as the square or cube of the
speed, this ac motor characteristic is usually adequate.
AC Motors - Constant torque:
These ac motors can develop the same torque at each speed, thus
power output varies directly with speed. For example, an ac motor
rated at 10 hp at 1,800 rpm produces 5 hp at 900 rpm. These ac motors
are used in applications with constant torque requirements such
as mixers, conveyors, and compressors.
AC Motors - Constant horsepower:
These ac motors develop the same horsepower at each speed and the
torque is inversely proportional to the speed. Typical applications
for ac motors include machine tools such as drills, lathes, and
milling machines.
AC Motors - Single-phase
AC Motors: Single-phase induction ac electric motors are commonly fractional-horsepower
types, although single-phase integral-horsepower are available in
the lower horsepower range. The most common fractional-horsepower
single-phase ac motors are split-phase, capacitor-start, permanent
split-capacitor, and shaded pole.
The ac motors come in multispeed types, but there is a practical
limit to the number of speeds obtained. Two, three, and four-speed
motors are available, and speed selection may be accomplished by
consequent-pole or two-winding methods.
Single-phase ac electric motors run in the direction in which they are started;
and they are started in a predetermined direction according to the
electrical connections or mechanical setting of the starting means.
General-purpose ac motors may be operated in either direction, but
the standard ac motor rotation is counterclockwise when facing the
end opposite the drive shaft. AC motors can be reconnected to reverse
the direction of rotation.
AC Motor: Basics of AC Motor Design Engineering
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