Question 1

Most service technicians test a three-phase motor with a(n) ____.&#10;A) voltmeter&#10;B) multimeter&#10;C) ammeter&#10;D) ohmmeter

Accepted Answer

ohmmeter

Question 2

Most starters use three transformers connected in an open delta.

Accepted Answer

Most starters use three transformers connected in a closed delta, not an open delta.

Question 3

Often it is necessary to reduce the inrush current during the starting period of large motors.

Accepted Answer

This is true as the inrush current can cause damage to both the motor and the electrical system. Various methods such as soft starters or reduced voltage starters can be used to limit the inrush current during motor starting.

Question 4

Interlocking is used to prevent one contactor being energized while some other contactor is energized.

Accepted Answer

Interlocking is a technique used to ensure that two or more contactors cannot be energized at the same time, thereby preventing accidental short circuits or other hazardous conditions.

Question 5

Motors intended for use with part winding starting contains two separate stator windings.

Accepted Answer

Motors intended for use with part winding starting do contain two separate stator windings.

Question 6

In an induction motor, the current flow in the rotor is produced by induced ____ from the rotating magnetic field of the stator.&#10;A) magnetism&#10;B) force&#10;C) pressure&#10;D) voltage

Accepted Answer

The current flow in the rotor is produced by induced voltage from the rotating magnetic field of the stator. This voltage induces a current flow in the rotor windings, creating a magnetic field that interacts with the stator's magnetic field, resulting in the rotation of the rotor.

Question 7

Which of the following is a determining factor in the amount of torque produced by an AC induction motor?&#10;A) The strength of the magnetic field of the stator&#10;B) Speed of the cutting action&#10;C) The length of the conductor&#10;D) The capacity of the magnetic field

Accepted Answer

The strength of the magnetic field of the stator is a determining factor in the amount of torque produced by an AC induction motor. The stator's magnetic field interacts with the rotor's magnetic field, causing the rotor to rotate and produce torque. The stronger the stator's magnetic field, the more torque the motor can produce.

Question 8

The greater the ____ between rotor and stator flux, the less torque that is developed by the motor.&#10;A) phase angle&#10;B) temperature difference&#10;C) distance&#10;D) tension

Accepted Answer

The torque developed by an AC motor is proportional to the product of the rotor current and the sine of the phase angle between the rotor and stator flux. Therefore, the greater the phase angle between the rotor and stator flux, the less torque is developed by the motor.

Question 9

In a wye connection, the line current is greater than the phase current by a factor of the square root of 3.

Accepted Answer

In a wye connection, the line current is equal to the phase current, whereas in a delta connection, the line current is greater than the phase current by a factor of the square root of 3.

Question 10

Which of the following is a determining factor in the amount of induced voltage?&#10;A) The ambient temperature&#10;B) The number of turns of wire cut by the magnetic field&#10;C) The capacity of the magnetic field&#10;D) The phase angle difference between stator and rotor flux

Accepted Answer

The amount of induced voltage is directly proportional to the number of turns of wire cut by the magnetic field according to Faraday's law of electromagnetic induction.

Deck 15: The Squirrel-Cage Induction Motor