Deck 5: Manual Starting of DC Motors

Question 1

Manual starters for DC motors are rare because ____________________ are much more efficient and practical.

Answer 1

electronic controls

Question 2

As described by NEMA (National Electrical Manufacturers Association), a(n) ____________________ is a device used to accelerate the motor to its rated speed in one direction and limit the current to the armature circuit to a safe value during starting and accelerating

Answer 2

starting rheostat
DC motor starter

Question 3

What are two inherent factors that limit the amount of current used by a motor that is supplied from a DC source?

Answer 3

Two factors limit the amount of current used by a motor that is supplied from a DC source: (1) the counter-electromotor force (CEMF) produced in the rotor by the spinning of the conductors through a magnetic field and (2) the actual resistance of the motor windings.

Question 4

In the configuration of a three-terminal starter connected to a shunt-wound motor, the tapped resistance is connected in series with the armature, yet the high resistance field receives full voltage immediately upon starting. What is the rationale for this voltage application?

Question 5

The reverse direction of a drum controller is accomplished by reversing the current in both the armature circuit and the shunt and series fields.

Question 6

A drum controller was used on crane motors, elevators, machine tools, and other applications in heavy industry.

Question 7

DC series motors that can run at no load may generate runaway speeds and literally throw themselves apart.

Question 8

The holding circuit for the controller of ____________________ motors is in series with the starting resistance.

Question 9

What mechanism is used to keep the cylinder and movable contacts stationary until the handle of the drum controller is moved by the operator?

Question 10

____________________ are used when an operator is controlling the motor directly.

Question 11

In terms of speed control, how does a four-terminal starter differ from a three-terminal starter?

Question 12

With a three-terminal starter, what change in the circuit is used to prevent a high-speed runaway of the DC shunt motor at no load?

Question 13

Drum controllers with more ____________________ allow for a greater control of speed.

Question 14

Three-terminal and four-terminal starting rheostats are still widely used.

Question 15

Drum controllers are still frequently used with AC as well as DC motors.