Chapter 17 Three-Phase Motors
True
A synchronous motor must never be started with DC current connected to the rotor.
False
An induction motor can always reach synchronous speed.
True
Induction motors can act as a generator.
True
Maximum torque is developed when stater and rotor flux are in phase with each other.
True
Single-phasing occurs when one line of a three-phase system is open.
S = 120•f/P S = Speed in rpm f = Frequency in Hz P = Number of stator poles (per phase)
Synchronous speed can be calculated using the formula ____
Wound-rotor
The _____ induction motor was very popular in industry for many years because of its high starting torque and low starting current.
True
The direction of rotation of any three-phase motor can be changed by reversing two of its stater leads.
rotating magnetic field
The principle of operation for all three-phase motors is the _______
f = P x Sr/120 f= Frequency in Hz P = Number of stator poles Sr = Rotor slip in rpm
The rotor frequency can be determined by using the formula ____
Amortisseur winding
The set of squirrel cage bars on a synchronous motor, used to start the motor, is known as the ______
synchronous speed
The speed at which the magnetic field rotates is called the ____
Percent slip
The speed performance of an induction motor is measured in ____
Squirrel-cage, wound rotor, synchronous
The three basic types of three phase motors are _____
Consequent pole
____ squirrel-cage motors permit the synchronous speed to be changed by changing the number of stator poles.
