Deck 15: Direct Current Motors

Question 1

There are several ways of controlling the speed of direct current motors. The method employed is generally dictated by the requirements of the load.

Answer 1

True

Question 2

Once horsepower has been converted to a basic unit of power, it can be converted to other power units, such as in the following: ____.

A) 1 W = 3.42 BTUs per hour
B) 4.99 W = 1 calorie per second
C) 155 W = 1 BTU per second
D) 2.36 W = 1 ft-lb per second

Answer 2

A

Question 3

The armature of a ServoDisc motor does not contain any copper.

Answer 3

False

Question 4

Most large compound direct current motors have a protective device connected in series with the shunt field called the ____ relay.

A) shunt loss
B) field loss
C) armature
D) shunt

Question 5

Permanent magnet direct current motors with iron armatures have a problem with cogging at high speeds.

Question 6

The efficiency of a motor can be found by using the following formula: (power out/power in) x 100.

Question 7

The following formula can be used to determine the speed of the rotating magnetic field when the frequency and number of stator poles per phase are known: S = ____.

A) 120 x (f / P)
B) 120 x f x P
C) (120 x f) / P
D) (120 - f) / P

Question 8

How much horsepower is being produced by a motor turning a load of 350 lb-in. at a speed of 1375 RPM?

A) hp = 0.765
B) hp = 7.65
C) hp = 76.52
D) hp = 765.19

Question 9

Some converters that supply power to brushless motors produce sine waves, but most produce a ____ waveform.

A) trapezoidal DC
B) triangular DC
C) hectagonal AC
D) trapezoidal AC

Question 10

The amount of counter-EMF produced in the armature is proportional to three factors: the number of turns of wire in the armature, the strength of the magnetic field of the pole pieces, and the speed of the armature.

Question 11

A motor is a device used to convert electrical energy into kinetic potential energy.

Question 12

In the right-hand motor rule, thumb = thrust or the ____.

A) direction of armature current
B) direction of magnetic field
C) strength of armature current
D) direction of armature rotation

Question 13

Series motors have the ability to develop extremely high starting torques. An average of about ____% of full torque is common.

A) 200
B) 275
C) 450
D) 500

Question 14

Brushless DC motors contain a wound armature and commutator but do not contain brushes.

Question 15

Compound motors can be connected as short shunt or long shunt just as compound generators can. They can also be cumulative-compounded motors or differential-compounded motors.

Question 16

Small permanent magnet motors are used as ____.

A) armamotors
B) revomotors
C) servomotors
D) polamotors

Question 17

Two factors that determine the amount of torque produced by a direct current motor are the strength of the magnetic field of the pole pieces and the ____.

A) strength of the magnetic field of the armature
B) direction of the magnetic field
C) direction of the turning force
D) strength of the magnetic lines of flux

Question 18

Many large DC compound motors intended to operate in an overspeed condition will actually contain three separate shunt fields.

Question 19

The speed regulation of a direct current motor is proportional to the resistance of the armature.

Question 20

____ motors are often referred to as constant speed motors.

A) Compound
B) Shunt
C) Series
D) Current