Deck 34: Variable Voltage and Magnetic Clutches

Question 1

Motors that are intended to operate with variable voltage are designed with ____________________ stators.

Answer 1

high impedance

Question 2

Magnetic clutches are divided into two primary sections. What are they?

Answer 2

Magnetic clutches are divided into two primary sections, the field section that contains the slip rings and coil winding, and the armature section that contains the clutch disc.

Question 3

What is the main advantage of an eddy current clutch?

Answer 3

The main advantage of an eddy current clutch is that there is no mechanical connection between the rotor and drum. Because there is no mechanical connection, there is no friction to produce excessive heat and there is no wear as is the case with mechanical clutches.

Question 4

Clutches cannot provide a smooth start for loads that can be damaged by sudden starting, or for high inertia loads such as centrifuges or flywheels.

Question 5

The problem with eddy current clutch circuits is that they lack a speed sensing device that automatically increases or decreases the DC excitation current when load is added or removed.

Question 6

What does the high impedance of the stator prevent?

Question 7

What are the disadvantages of motors that contain high impedance stator windings?

Question 8

Motors that used a centrifugal switch to disconnect the start windings cannot be used with variable voltage control.

Question 9

Figure 34-8
In the accompanying diagram, what do part A and part B show?

Question 10

Double-face clutches have both the armature and field discs mounted on the same hub.

Question 11

Only triac controls that are designed for use with ____________________ loads should be used to control a motor.

Question 12

____________________ are used in applications where it is desirable to permit a motor to reach full speed before load is applied.

Question 13

Figure 34-6
The accompanying diagram has a double-face magnetic clutch.

Question 14

One method of obtaining a variable AC voltage is with the use of an autotransformer with a sliding tap. The sliding tap causes a change in the turns ratio of the ____________________.

Question 15

A(n) ____________________ is a solid-state device similar to a silicon controlled rectifier (SCR), except that it will conduct both the positive and negative portions of a waveform.