Deck 22: Ac Series and Repulsion Motors

Question 1

____________________ losses traditionally made up about 66% of the power losses in the I2R losses of the stator windings.

Answer 1

Stator

Question 2

Briefly describe the advantage of using an integrated electronic drive and motor combination.

Answer 2

An integrated electronic drive and motor combination provides for perfectly matched components and easy, one-step, no-engineering installation.

Question 3

Briefly explain the cooling technique provided by a totally enclosed, fan-cooled (TEFC) motor.

Answer 3

TEFC motors have external fins on the motor that radiate the heat to the motor surface. An external fan then blows ambient air over the fins to cool the motor. The fan is attached to the motor shaft and runs at the same speed as the motor shaft.

Question 4

The ____________________ laws state that the energy required to drive fans or pumps (motors used for moving volumes of air or water) is proportional to the cube of the speed.

Question 5

Power factor typically improves with the hp rating of the motor and tends to peak about 75% to 100% of full load.

Question 6

To reduce losses due to eddy currents in the motor, high-grade steel with a higher silicon content is used to reduce the friction of the magnetic materials and therefore reduce the heat produced in changing the magnetic fields of the motor iron.

Question 7

If a motor is more efficient, it means that a higher percentage of the ____________________ measured in electrical watts is converted to output mechanical horsepower, compared to a lower efficiency motor.

Question 8

I2R losses can be reduced by decreasing the wire size in the stator winding.

Question 9

Standard motor efficiency is calculated by the simple formula of watts output of the motor divided by watts input.

Question 10

A high-efficiency motor is designed to run at 94.1% efficiency at full load.

Question 11

A(n) ____________________ motor is designed to run at 91.0% efficiency.

Question 12

List the four categories of motor losses that affect motor efficiency.

Question 13

Identify two benefits of a premium efficiency motor running at a cooler temperature.

Question 14

What is the formula for calculating input wattage in a three-phase motor?

Question 15

____________________ occur because the magnetic flux created in the stator is lost and never reacts with the rotor conductors to produce torque.