Motors Flashcards
Since flux lines repel each other laterally, the stator flux is distorted by the rotor flux. Torque develops and causes the motor to turn clockwise, which is called _____..
Motor action
What is the difference between the rotor of a wound rotor motor vs SCIM?
Wound roter has insulated wire wound on poles whereas SCIM is uninsulated and on bars.
The closer the rotor voltage and current are to being in phase, the better the _____.
Torque of the motor
If the resistance in a wound rotor motor is not removed, the motor will _____ full rated speed at full load.
Not reach
Is operating a wound rotor motor at a reduced speed by using secondary resistors efficient? What does it effect?
Not efficient. Increases speed regulation.
Motors with higher ______ rotor speeds have lower _____ and higher _____
Full load, % speed regulation, efficiencies.
The resistance of a wound rotor motor is adjusted using external resistance connected through ______ and _____
Brushes and slip rings
How do induction motors act like transformers?
Rotor current reflected to stator using winding ratios, as motor accelerates stator current also changes magnitude and pf. Basically, transformer action.
Current in a motor is not proportional to ______ and _____ even though it increases with them
Power and torque
What is used to measure a motor’s range of running speeds?
Tachometer
A 3 phase induction motor typically draws about __________ times it’s full load current when started across the line at full voltage.
5 or 6
What type of reduced voltage starter doesn’t actually reduce voltage?
Part winding starter & motor
Static and rotary phase converters produce different output _____ as the load changes.
Current
Which phase converter is better for variable loads?
Rotary
In a rotary phase converter, the motor-generator doesn’t start until _____.
The motor-generator accelerates to rated speed
Phase converters are used in areas with single phase service such as: (x4)
Farms, small industrial plants, woodworking shops, metal fab shops
Single phase motors are not available above __ hp and not common above __ hp
15, 5
How does an electronic soft starter work? Once the motor has accelerated, what happens?
Reduce starting current with network of electronic switches and programmable chips on printed circuits.
Once accelerated, a conventional contact closes to bypass the electronic switches and apply full voltage to motor.
Kick starting is another term for what?
Initial current surge for loads that require extra torque to overcome interia of load at rest
Variable torque loads require __ power and __ torque when at half soeed
1/8, 1/4
Constant torque loads require __ power at half speed but _____ torque
Same
How do you calculate the line current and torque for reduced stating autotransformers?
Tap setting squared. Ie 2A x 08(sq)
Fractional horsepower single phase motors are _____ than fractional horsepower three phase motors.
Cheaper
Integral horsepower motors are cheaper when they are three phase or single phase?
Three phase
A three phase motor load should be applied _____ the rotary phase converter is started.
As soon as
A rotary phase converter can supply only one three phase motor, true or false?
False
Nameplate rating of a rotary phase converter is listed in _____.
Running KVA and max starting HP
What are two ways to adjust how closely balanced the three phases supplied by a rotary converter?
Adding load, and switching in/out capacitance
