Motors and transformers Flashcards
When is torque at a maximum in a squirrel-cage induction motor?
When the phase angle between the stator and rotor fields is 0 degrees.
What is a squirrel-cage rotor constructed from?
Bars and rings embedded in steel laminations
To run a dual voltage motor on the lower of the two voltages the windings must be connected _____
In Parallel
To run a dual voltage motor on the higher of the two voltages the windings must be connected _____
In Series
What equipment is used to test the rotation direction of a new motor?
A Phase Rotation Meter
How do you reverse the direction of any three phase motor?
Switch any two T leads feeding the motor
What is synchronous speed?
The speed of rotation of a motors magnetic field
Is a synchronous motor the same as an induction motor?
No
What is rotor frequency?
The voltage induced by the rotor being cut by the magnetic field. it is lower than the synchronous frequency.
What percent slip is normal for a squirrel-cage induction motor?
2-5%
When a squirrel-cage motor is first started the value of current draw is _____.
Several times the running current
What effect do different shaped rotor bars have on a squirrel-cage motor?
They change the starting torque of the motor
What is single phasing?
When one phase of a three phase motor opens and causes failure
What happens when the polarity of half the pole windings is reversed in a consequent pole motor?
The number of poles is doubled and the speed of the motor is cut in half
The differential selsyn has three stator windings connected in a wye and a rotor made up of _____.
Three windings connected in a wye
