AC Motors Flashcards
Advantages of AC vs. DC
Simpler to construct, rugged, durable, and efficient.
AC Motor Motion
The result of the interaction between a rotating magnetic field (stator) and a conductor (rotor) in response to electromagnetic induction.
squirrel cage rotor
The bars are connected to each other by a copper or aluminum ring or plate on both ends and are imbedded in a laminated core. .
Stator
A stationary part that consists of a steel frame housing which supports the stator (field) windings.
Slip
The difference between rotor speed and field speed.
What is the purpose of slip?
If the rotor were to rotate as fast as the field, there would be no relative motion. As a result, the rotor must rotate slightly slower than the field.
synchronous speed
The speed of the rotating magnetic field of an induction motor.
Motor Ratings
Motors can be grouped into one of three broad power ratings:
integral horsepower (ihp), fractional horsepower (fhp), and sub fractional horsepower (sfhp)
Voltage Rating
The voltage at which the motor may be operated plus or minus 10 percent.
Current Rating
Normal running current drawn at rated load, rated voltage, and rated frequency.
Horsepower Rating
The number, or fractional part, of a horsepower the motor will produce at rated speed.
RPM or Rated Speed
The speed the motor will produce at rated horsepower, voltage and frequency.
Duty Rating
The period of time the motor may be operated without overheating. Generally this is continuous.
Temperature rise
The amount by which a motor, operating under rated conditions, is hotter than its surroundings.
Temperature (amb)
The temperature of the space around the motor.
Insulation Class
Motor insulation is grouped into classes. The maximum temperature at which a motor should operate depends on the type of insulation used on the motor windings.
Service Factor Rating
The service factor is a number that can be multiplied by the horsepower rating to determine the maximum continuous horsepower output of the motor.
Open Motors Enclosure
Enclosures with ventilating openings that allow surrounding air to be forced through the enclosure to cool the motor.
Totally Enclosed Motors
Motors which do not allow free exchange between surrounding air and air within the enclosures.
Single-Phase Induction Motors
Without starting assistance the rotor does not move and the motor hums without turning.
Split-Phase Motor
A type of single-phase induction motor in which the stator is provided with a starting or auxiliary winding (S) and a main or running winding (M). The out-of-phase currents produce the rotating field which is necessary to develop a starting torque.
Capacitor-Start Motor
A motor that uses a capacitor in series with the start winding that causes the current in that winding to lead the run winding.
Single-Value Capacitor Motor
A motor that has a run and start winding with a capacitor permanently connected in series with the start or capacitor winding.
