Deck 36: Variable Frequency Control S

Question 1

How can the speed on a three phase induction motor be controlled?

Answer 1

The speed of a three phase induction motor can be controlled by either changing the number of stator poles per phase, as is the case with consequent pole motors, or by changing the frequency of the applied voltage.

Question 2

Changing frequency causes a corresponding change in the inductive reactance of the windings.

Answer 2

True

Question 3

Drives using Insulated Gate Bipolar Transistors (IGBTs) generally used ____________________ to rectify the AC voltage into DC.

Answer 3

diodes

Question 4

The Insulated Gate Bipolar Transistor (IGBT) is a current controlled device, not a voltage controlled device.

Question 5

Alternators are often used to control the speed of several induction motors that require different changes in speed.

Question 6

Variable frequency drives intended to control the speed of  motors up to 500 HP generally use ____________________.

Question 7

What is an advantage of using Insulated Gate Bipolar Transistors (IGBTs) for drives?

Question 8

Inverter rated motors are specifically designed to be operated by variable frequency drives.

Question 9

The output frequency of the alternator is determined by the speed of the ____________________.

Question 10

Ramping permits the motor to bring the load up to speed slowly as opposed to simply connecting the motor directly to the line.

Question 11

How do most variable frequency drives operate?

Question 12

Many transistor controlled variable frequency drives now employ a special type of transistor called a(n) ______________________________.

Question 13

When bipolar junction transistors are employed as switches, they are generally driven into ____________________ by supplying them with an excessive amount of base-emitter current .

Question 14

What are thyristors?

Question 15

What are two basic methods of achieving variable frequency?