Deck 13: Multispeed Motors

Question 1

The output voltage to the motor is controlled by pulse width modulation (PWM).

Answer 1

True

Question 2

Variable frequency drives intended to control motors over ____ generally use SCRs or GTOs (gate turn off device).

A) 200 horsepower
B) 300 horsepower
C) 400 horsepower
D) 500 horsepower

Answer 2

500 horsepower

Question 3

In the air conditioning field, variable frequency drive is ____ used to control the speed of blower motors.

A) never
B) often
C) always
D) rarely

Answer 3

often

Question 4

The primary purpose of a variable frequency drive is to provide speed control for an AC motor.

Question 5

The ____ of the rotating magnetic field of an AC induction motor can be changed by changing the number of stator poles.

A) acceleration
B) mass
C) density
D) speed

Question 6

Current limit controls set the ratio by which the voltage increases as frequency increases or decreases as frequency decreases.

Question 7

Multispeed AC motors have been used to a great extent in the air conditioning field for many years.

Question 8

The consequent pole motor can be used to operate ____, such as two-speed compressors.

A) light loads
B) rotating masses
C) heavy loads
D) accelerating masses

Question 9

SCRs and GTOs are thyristors and have the ability to handle a greater amount of ____ than transistors.

A) current
B) electric charge
C) voltage
D) resistance

Question 10

Most transistor-controlled variable drives no longer employ insulated gate bipolar transistor (IGBT) transistors.