Unit 33: Three - Phase Motors
Dual voltage motors have ___ or ____ leads brought out of the terminal box
9 or 12
Wound rotor motors have higher starting _____ and lower starting _____ than squirrel cage motors of the same horsepower
TORQUE / CURRENT
The ______ on the nameplate indicates the type of rotor bars used
code letter
The speed of a wound rotor motor can be controlled by ____
connecting resistors to the rotor windings
Synchronous motors operate at a ______ speed from no load to full load
constant
A ______ is connected across the rotor winding during starting to prevent high voltage in the rotor due to induction
field discharge resistor
Dual voltage motors intended for _____ connection have their phase windings connected in parallel
low voltage
The direction of rotation of a three phase motor can be changed by ___
reversing two of the stator leads
Maximum torque is developed when ____ and _____ are in phase with each other
stator and rotor flux
What happens when load is connected to a synchronous motor?
stress develops between the magnetic fields of the rotor and stator
Synchronous motors operate at _____
synchronous speed
The speed of the rotating magnetic field is called _____
synchronous speed
Consequent - pole squirrel cage motors change speed by changing _____
the number of stator poles
Changing DC excitation to a synchronous motor has does not affect _____
the speed of the motor
DC excitation can be provided to a synchronous motor by 2 ways which is ___
though two sliprings or brushless excitation
The type ___ rotor has the lowest starting CURRENT, highest starting TORQUE, and poorest SPEED REGULATION
A
____ motors are used to provide position control and angular feedback information
Selsyn
The direction of a three phase motor can be checked by _____
a phase rotation meter
Selsyn motors have three phases and operate on _____
single phase AC
Three basic types of three phase motors are_____
1. Squirrel cage induction motor 2. Wound rotor induction motor 3. Synchronous motor
Three factors that cause a magnetic field to rotate are ____
1. The fact that the voltages of a three phase system are 120 out of phase with each other 2. The fact that voltages change polarity at regular intervals 3. The arrangement of the stator windings
Two factors that determine the synchronous speed are ___
1. The number of stator poles per phase 2. The frequency of the applied voltage
The double - squirrel cage rotor contains ____ sets of windings
2
Synchronous motors must have ______ from an external source
DC excitation
All three phase motors operate in the principle of ______
a rotating magnetic field
Three factors that determine the torque produced by an induction motor are ___
1. The strength of the magnetic field of the stator 2. The strength of the magnetic field of the rotor 3. The phase angle difference between the rotor and stator flux
Wound rotor motors have wound rotors that contain ____
three slips rings for three windings in the rotor to connect to an external source (resistors for polar crane)
Synchronous motors have a set of type A bars used for _____. This winding is call the _____ winding
starting / amortisseur
Dual voltage motors intended for _____ connection have their phase windings connected in series
high voltage
Synchronous motors can produce a _____ power factor by overexcitation of the DC supplied to the rotor
leading