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Motor & Generator Theory > Gerrish Book > Flashcards

Gerrish Book Flashcards

1
Q

A __________ is used to maintain a constant direction of current from the armature.

A

Commutator or split rings

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2
Q

Difference between slip rings & split rings;
Slip rings are __C and split rings are __C.
Slip rings are in _______ contact with brushes, Splits are ____.
Slips, ______ changes; Splits, the AC in the armature is changed to a __________ DC.

A

AC, DC
Constant, not
Polarity, pulsating

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3
Q

Name 3 types of generator losses.

A
  1. I (squared) R
  2. Eddy Currents
  3. Hysterisis
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4
Q

I (squared) R losses is when resistance _______ and power loss _________.

A

doubles

quadruples

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5
Q

Eddy currents = alternating currents flowing in ____, caused by _______ voltages and ________ by laminations.

A

core
induced
decreased

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6
Q

Hysteresis = internal molecular ________ between ________ particles that creates a ____ loss. Decreased by _______ steel.

A

friction
magnetic
heat
silicon

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7
Q

Generator output is determined by what two items?

A
  1. Strength of magnetic field

2. Speed of rotation

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8
Q 
What kind of generator requires an external power source to provide voltage to the field windings:
A. Series generator
B. Compound generator
C. Shunt generator
D. Separately excited field generator
A

D. Separately excited field generator.

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9
Q 
This generator is considered a constant voltage device:
A. Series generator
B. Compound generator
C. Shunt generator
D. Separately excited field generator
A

C. Shunt generator

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10
Q 
This generator has both series and shunt windings in the field. 
A. Series generator
B. Compound generator
C. Shunt generator
D. Separately excited field generator
A

B. Compound generator

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11
Q

State the mathematical equation for regulation of a power source.

A

E (no-load) - ( full load ) / E (full load) x 100 = % regulation

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12
Q

What is meant by three-phase power.

A

Each phase develops positive and negative peaks at different times that are120 degrees apart.

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13
Q

A delta connected generator has its winding connected in series or parallel?

A

Series

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14
Q

A three-phase power generator supplied 120/208 volts, would it most likely be from a delta or wye connection generator?

A

Wye

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15
Q

What three characteristics must match before you can connect two generators in parallel?

A
  1. Frequency
  2. Voltage
  3. Instantaneous polarity
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16
Q

What are the three major causes of generator failure?

A
  1. Excessive brush wear.
  2. Excessive bearing wear.
  3. Electrical overload.
17
Q

How may a self excited generator lose its residual magnetism?

A

Heat from excessive overload.

18
Q

The motor is used to convert _________ energy into __________ energy.

A

electrical

mechanical

19
Q

Outline how a simple dc motor operates.

A

A external power source energizes an armature coil which rotates a commutator that cuts the magnetic field inducing the energy.

20
Q

The turning power of a motor is called the ______.

A

torque

21
Q

How is counter emf generated in a dc motor?

A

If the motor were connected to a prime mover & rotated in the same direction as the dc motor, it would produce a voltage with the opposite polartity.

22
Q

What is the recommended maximum fuse size for a dc motor?

A

A fuse that is no more than 150% of the full load current.

23
Q

An ________ is a smaller field pole placed midway between main field poles.

A

Interpole

24
Q

Give the formula to find percent of speed regulation.

A

Speed no-load - Speed full load / Speed full load x 100% = % of speed regulation

25
Q

Name the key advantage of a series motor.

A

Its ability to develop a high torque under load.

Load; low arm. speed & cemf = high arm. current & increased torque.

26
Q

There are two types of compound motors. Name them.

A
  1. Cumulative

2. Differential

27
Q

Some automatic starting switches contain _______ __________ that will not close until the current has decreased to a preset value.

A

armature contactors

28
Q

A ______ controls a half-wave of ac.

a. SCR
b. Triac
c. Universal motor
d. None of the above

A

SCR ( silicon controlled rectifier)

29
Q

Lenz’ Law: the field _______ around conductor is _________ by the ________ field

A

induced
opposed
existing

Motor & Generator Theory (6 decks)

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