Deck 36: Variable Frequency Control

Question 1

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

Answer 1

True

Question 2

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

Answer 2

IGBT
Insulated Gate Bipolar Transistor
IGBT (Insulated Gate Bipolar Transistor)

Question 3

What are thyristors?

Answer 3

Thyristors are solid-state devices that exhibit only two states of operation, completely turned on or completely turned off.

Question 4

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

Question 5

How do most variable frequency drives operate?

Question 6

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

Question 7

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

Question 8

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 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

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

Question 14

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

Question 15

What are two basic methods of achieving variable frequency?