Test #4 Flashcards
(37 cards)
A ____ converts electrical energy to mechanical energy.
Motor
Name two main classifications of ac motors.
- single phase
- poly phase
What are the three types of ac induction motors? Describe them.
- split-phase motor: one centrifugal switch
- capacitor-start motor: has both centrifugal switch and capacitor
- permanent-split capacitor motor: has only capacitor
Name the three types of dc motors. Describe them.
- shunt-wound motor: shunt field and armature are on different lines
- series-wound motor: series shunt and armature are on same line
- compound-wound motor: both motors combined, shunt field on top line while series and armature are on middle line
____ a force that produces rotation.
Motor Torque
List four general factors used to make a proper motor selection.
- power source
- temperature
- environment
- load
Name three factors that affect motor enclosure selection.
- environment
- supplied equipment
- availability
Most motors are built to withstand minor ___.
Over-loads
Maximum output = ?
hp x service factor
What four situations determine how circuits are sized?
- circuit supplying a single motor
- circuit supplying several motors & other loads
- multi motor & combination-load equipment
- rating & size of motor load
Current drawn by a motor is initially large, but stabilizes to the ____ current.
Full-load
What carries 500% of its rating for up to 10 seconds, allowing more time for the current drawn by the motor to stabilize?
Time-delay
What is read by the power company’s wattmeters for billing purposes?
True power
If the true power and apparent are equal, the power factor would be ____.
1 or 100%
Power companies impose penalties or higher rates for customers whose power factor is below a set limit, normally ____.
90%
How are lower power factors imposed?
By adding capacitors to the circuit or by reducing the lag between the current & voltage.
A ___ regulates the power supply to a motor.
Motor controller
Motor starters are rated for motor horsepower and ____.
Full-load current
Name two common classes of starters.
- manual starters
- magnetic starters
Which starter is a simple, mechanical on-off switch?
Manual starters
Why is it important to be extremely cautious when servicing two-wire circuits?
These circuits provide low-voltage release without the protection, so if the motor stops, there’s no way of knowing when it’ll start again.
If power is interrupted, a ____ circuit will not automatically restart a motor when power is restored.
Three-wire
A motor control circuit normally operates at how many volts or less?
120 V
When several motors are controlled from a central location, it is call a ____.
Motor control center
