Ac Motors Flashcards
(27 cards)
What are the two basic classes of motors?
Ac
Dc
What voltages are Ac motors rated in?
120vac
208vac
240vac
480vac
600vac
What is two numbers for frames divided by?
16ths
What is three digits divided by one frames?
4ths first two numbers
Frame letter meanings
T- long shaft
TS - short shaft
C- c-face motor
TC - c - face with long shaft
JM,JP - close coupled
U- France size horsepower relation ship
TZ - special shaft dimensions
TY- special mounting
What are factors that cause motors to overheat?
High or low voltage supply
Slow or repeated starts
High ambient temperatures
Blocked vent holes
Voltage imbalance on three phase
Motor insulation is also known as?
Motor class
On motor class what do the letters stand for?
A- 221 degrees
B- 266 degrees
F- 311 degrees
H 356 degrees
What is service factor?
The amount of overload a motor can take without overheating
On service factor 1.15 is what?
115 percent
On a speed torque curve when speed is low torque is what?
High.
Unless a centrifugal clutch then it’s opposite
What are the two optional mounting positions for motors?
C- face - motor attaches directly to endbell
D - flange - has a mounting flange allows motor to be noted directly onto the driven machinery
How do you protect fractional horsepower motors from overheating?
Manual thermal overload (MTO)
Or automatic thermal overload (ATO)
How to keep large horsepower motors from overheating? (Three phase motors)
Built into windings
Thermostats
Thermistors
Resistance temperature detectors
Most common thermal overloads
What is the flow of electrons?
Electric current
Can single phase and three phase motors be interchangeable?
No
Should use three phase motor if available they are cheaper.
What are the two main parts of a ac motor?
Rotor
stator (stationary part outer shell)
What is a set of windings called?
Poles ( the number of poles determines horsepower)
What is “slip”
The difference between the synchronous speed and the actual rotor speed.
(Must be some slip for induction motor to operate) 1-5 percent
Why are three phase induction motor most commonly used?
High efficiency, low cost (workhorses of industry)
Single phase induction motors.
The rotating magnetic field does not exist until running rpm is reached. No starting torque so manufactures have to include design mechanisms to cause the motor to start.
Different techniques to help single phase induction motors to start.
Shaded pole
Split phase
Capacitor start
Permanent split capacitor
What motor has a copper loop called a shading ring surrounding a portion of each starter pole?
Shaded - pole motor
What motor has two sets of stator windings one start and one run. Start windings positioned 90 degrees to run windings and shift the magnetic field by 25 degrees. Has a switch built in to disconnect start windings when motor is at 3/4 synchronizes speed
Split phase motor
