What factors help to determine the amount of torque developed by an electric motor?
strength of magnetic field developed by amount of current
Explain the significance of each digit of the right hand in describing "the right hand motor rule"
thumb=direction of motion
index=fixed field of flux
middle=current flow
what is the best method of controlling the RPM of a DC motor?
Control the amount of field current. Less field current, higher RPM
How can the direction of rotation of a DC motor be reversed? When will this be done?
By changing the direction of current flow either in the armature or in field winding, not both.
what are the 3 types of DC motors?
Series, shunt and compound.
this cuts power to starter when current drops below specified limits
under current relay
what type of energy losses exist in DC motor
Copper & Iron loss
disadvantages of a series type DC motor?
poor voltage regulation under changing load
No speed control, may self destruct if over-sped
what is the biggest advantage of a shunt type dc motor?
speed regulation- maintains constant speed
Advantages of AC motors over DC
Light weight, more efficient, suitable for constant speed, good starting torque
what is a universal motor??
DC series motor that operates on AC, possible on DC.
if an inspection of dc motor shows brittle discolored wire insulation of field winding, what does this indicate?
overheating, overload, bearing problems
what is the most common type of dc motor used in aircraft engine starting application
series
Biggest disadvantage of shunt type DC motor?
Increase of load, decrease in voltage. Poor torque
rotor assembly type of AC induction motor
squirrel cage
what is slip
difference between motors sync speed and actual shaft speed
function of the centrifugally operated switch found in most single phase ac..
disconnects start winding after the motor reaches 25% of its speed
3 basic types of single phase AC induction motor
split phase, capacitor start and shaded pole
direction of rotation of a shaded pole is determined by
where the shading ring is
why is # of poles per phase important?
to determine syncronous speed
a certain electric motor develops 6.3 ft/lbs of torque at 2500 rpm... What is the HP rating????
2.99 HP (3)
What happens to the counter EMF developed in the armature of a motor as the motor's RPM's increase. What effects does this have on the motors ability to generate torque?
As motors rpm increases, so does the EMF, this causes less armature current and weakening ability of the motor to generate torque.
how is the rotation of a shaded single phased motor changed?
only by changing the position of the shaded portion of the poles
a certain motor is rated at 3.73 KW.. what is its HP rating???
5HP
most common trouble of an induction ac motor
bearings