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Exam 3: Three-Phase Motor Theory

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Question 1

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What are the two advantages of using electro-magnets to create a magnetic field?

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First, the strength of the magnetic fiel...

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Question 2

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Squirrel cage induction motors are sometimes referred to as ____ speed motors.

A) constant
B) rotor
C) electric
D) coil

E) A) and B)
F) A) and D)

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Question 3

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The induced voltage in the rotor is ____________________ to the number of lines of magnetic flux cut, so the induced voltage will be at its maximum, because the maximum lines of flux are cut when the rotor is standing still.

In three-phase motors, a rotation would quickly become evident as each set of poles created their magnetic fields ____ degrees out of phase with each other.

Induction motors depend on the forces of attraction and ____________________ caused by the magnetic field pole polarities interacting between the stator and the rotor, to create a turning torque force on the rotor.

The law of charges states that like polarity charges will repel, and unlike polarity charges will attract.

Squirrel cage induction motors are sometimes referred to as constant speed motors.

The ____ speed of an electric induction motor is the speed at which the magnetic field rotates around the stator.

At ____, the maximum positive voltage on the coils would cause the maximum positive current, which would create the maximum magnetic flux, and the strongest magnetic north polarity pole at each of the coils.

The rotor of an induction motor must always turn sufficiently faster than the rotating magnetic field so that magnetic lines of flux will cut through the rotor bars and induce a voltage.

What is the mathematical formula for making a synchronous speed calculation?

At ____, there is no voltage on the coils, so no current would flow through the coils, which means there is no magnetic flux, and no magnetic field or pole polarity.

Induction motor stators have coils of wire placed in the center of the stator core, which form electro-magnets when energized and create magnetic pole fields.

It is completely possible for the rotor of an induction motor to turn at synchronous speed and still produce turning torque.

The law of ____ simply states that like polarity charges will repel, and unlike polarity charges will attract.

The number of poles, combined with the alternating current frequency (HZ) , determines the synchronous speed ____ per minute (RPM) of induction motors.

The RPM speed difference between the stator rotating magnetic field, synchronous speed, and the actual rotating speed of the rotor, is called ____.

When first energized with the full supply voltage, the motor will draw the highest current the motor can draw, which is called the ____.

____________________ motor stators have coils of wire placed around the circumference of the stator core, which form electro-magnets when energized, and create magnetic pole fields.

The synchronous speed of an electric induction motor is the speed at which the magnetic field rotates around the stator.