420 Electrical Power Systems Technology
and circuit breakers mounted in a common enclosure. They are used on
systems of 600 volts or less.
Criteria for Selecting Motor Controllers
There are several important criteria that should be considered when
selecting electric motor controllers. Among these are:
- The type of motor-AC or DC, induction or wound rotor.
- The motor ratings-voltage, current, duty cycle, and service factor.
- Motor operating conditions-ambient temperature and type of atmo-
sphere. - Utility company regulations-power factor, demand factor, load re-
quirements, and the local codes. - Type of mechanical load connected to motor-torque requirement.
In order to become more familiar with the criteria listed above, you
must be able to interpret the data on a motor nameplate. The information
contained on a typical nameplate is summarized as follows:
Manufacturing Co.—The company that built the motor.
Motor Type—A specific type of motor, that is: split-phase AC, universal,
three-phase induction, et cetera.
Identification Number—Number assigned by the manufacturer.
Model Number—Number assigned by the manufacturer.
Frame Type—Frame size defined by NEMA.
Number of Phases (AC)—Single-phase or three-phase.
Horsepower—The amount produced at rated speed.
Cycles (AC)—Frequency the motor should be used with (usually 60 Hz).
Speed (r/min)—The amount at rated hp, voltage, and frequency.
Voltage Rating-Operating voltage of motor.
Current Rating (amperes)—Current drawn at rated load, voltage, and
frequency.
Thermal Protection—The type of overload protection used.
Temperature Rating (°C)—Amount of temperature that the motor will rise
over ambient temperature, when operated.
Time Rating—Time the motor can be operated without overheating
(usually continuous).
Amps—Current drawn at rated load, voltage, and frequency.