LVL 1
What is the purpose of the stator in a 3-phase motor?
To convert electrical energy to the energy of a magnetic field.
How many stator windings are there per pole in a 3-phase motor?
Three
A(n) _____ is the base unit of electrical power.
watt
_____ increases with increasing frequency and decreases with decreasing frequency.
Inductive reactance
____ is the power drawn by a motor that produces useful work.
True power
True or False
Constant-torque motors are used for loads that require the same horsepower output at different speeds
False
Apparent power is the vector sum of ____ and ____.
Motor power is rated in ___ or ___.
horsepower - watts
Apparent power is measured in ___ or ___.
volt-amps/kilovolt-amps
List the three parts of the rotor.
core-windings-shaft
The ____ of 3-phase motors can be reversed by interchanging any two of the 3-phase power lines to the motor.
direction of rotation
List the 5 types of energy loss in a motor.
resistance, core, bearing, windage, and sound.
What is the power factor on a 480-volt, 60-horsepower, 3-phase motor with an efficiency of 85% when the full load current is 70 amperes?
91% or .905
What is the power factor on a 240-volt, 5-horsepower, 3-phase motor with an efficiency of 95% when the full load current is 12 amperes?
79%
0.787
What is the power factor on a 480-volt, 25-horsepower, 3-phase motor with an efficiency of 75% when the full load current is 36 amperes?
83% or .083