Ac Motors Flashcards
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