Flashcards in AC Motor Test Deck (21):
What is the principle of operation of all three phase motors?
Rotor flux caused by current induced by flux of stator
The core of the stator and the rotor are laminated to reduce the effect of hysteresis.
At 10% drop in supply frequency or clause the synchronous speed of a squirrel cage induction motor to blank
Decelerate at a linear rate
What type of current flow produces flux in the rotor circuit of a three phase induction motor?
Induced AC current
What is the synchronous speed of a three phase 5 hp 240 V 12 amp 60 Hz for pole motor?
A three phase induction motor will always have a rotor speed that is blank the stator synchronous speed
Three phase 600 V 60 Hz four pole motor will induce four poles on it's rotor
How many poles must the stator of a three phase 600 V 60 Hz 10 hp 795 RPM motor contain?
Using compressed air to clean dust from inside the motor is preferred maintenance procedure.
What must be the duty cycle of the field resistors of a wound rotor motor shown below?
How do we reverse the direction of the wound rotor motor shown above?
Interchange any two stator leads
Using a wound rotor motor what is the common position of the speed controller rheostats at start up?
If we connected jumpers across the slip rings of the unloaded motor from question 12 what would be the starting characteristics of the motor?
Low torque high speed
Leaving the starting resistors in the rotor circuit improve the running efficiency of the wound rotor motor circuit
How does the wound rotor motor minimize a loss of starting torque?
By having a rotor power factor closer to unity
As the wound rotor motor accelerates which of the following is true of the rotor circuit?
The rotor impedance is decreasing
What current will flow in the amortisseur winding of the synchronous motor?
Induced AC current
How is the field excitation supplied to a synchronous motor?
From a DC source
What are the two main components of a brushless exciter for a synchronous motor?
Alternator and rectifier
How is the excitation current applied to the road or in the case of synchronous motors with external converters?
With brushes on slip rings