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