Deck 17: Solid-State Dc Drives and Starting Methods for DC Motors

Question 1

Most of the solid-state motor controllers intended to provide the DC power needed to operate large DC motors convert three-phase AC voltage directly into DC voltage with a three-phase _____.

A) bridge rectifier
B) resistor
C) capacitor
D) shunt

Answer 1

bridge rectifier

Question 2

The greatest advantage of using direct current motors is their _____ characteristic.

A) shuntless
B) constant speed
C) resistance-free
D) variable speed

Answer 2

variable speed

Question 3

A large diode is often connected across the output of the bridge. This diode is known as a freewheeling, or ____________________, diode and is used to kill inductive spike voltages produced in the armature.

Answer 3

kickback

Question 4

Discuss the shunt field power supply.

Question 5

How is output voltage control achieved?

Question 6

Small DC motors are often started directly across-the-line because they have high inertia.

Question 7

When large DC motors are to be started, current in-rush to the armature must be limited.

Question 8

Direct current is ____ difficult to interrupt than alternating current because it ____ to zero at periodic intervals.

A) more; falls
B) more; does not fall
C) less; falls
D) less; does not fall

Question 9

Most DC motor control circuits use a ____ current relay (FCR) or field loss relay connected in series with the shunt field of the motor.

A) fire
B) field
C) fixed
D) first

Question 10

Contactors that are designed to control direct-current devices are generally of the ____________________ type.

Question 11

If the motor is running and the shunt field opens, the motor will become a(n) ____________________ motor and begin to increase rapidly in speed.

Question 12

What is the difference between a pick-up coil and a holding coil?

Question 13

What is one way of limiting current in-rush?