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Motors & Generators > Review > Flashcards

Review Flashcards

1
Q

What is a generator?

A

A device that converts mechanical energy to electrical energy

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2
Q

What does a commutator in an AC generator do?

A
  • Changes AC voltage to DC voltage
  • Provides connection to the outside circuit via brushes
  • Provides connection for the windings in the armature
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3
Q

Describe series field windings.

A
  • Large wire with few turns

- Low resistance

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4
Q

Describe shunt field windings.

A
  • Small wire with many turns

- High resistance

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5
Q

What is the output voltage of a generator proportional to?

A
  • Strength of magnetic field of the pole pieces
  • Speed of rotation of the armature
  • # of turns of wire in armature
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6
Q

What happens when load is added to a series generator?

A

Output voltage increases

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7
Q

What happens when load is added to a shunt generator?

A

Output voltage decreases

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8
Q

What are the characteristics of a self-excited shunt generator?

A

It has residual magnetism in the pole pieces which produces initial output voltage

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9
Q

How is the output voltage of a DC generator that does not contain a separate voltage regulator generally controlled?

A

A large value variable resistor is connected in series with the shunt field

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10
Q

A DC generator is over-compounded when…

A

The output voltage is higher at full load than it is at no load

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11
Q

What determines the voltage regulation of a DC generator?

A

The resistance of the armature

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12
Q

What does it mean when a DC machine is cumulative-compounded?

A

The series and shunt field aid each other in the production of magnetism

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13
Q

What determines countertorque in a generator?

A
  • strength of the magnetic field of the armature

- strength of the magnetic field of the pole pieces

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14
Q

______ is the twisting or bending of the magnetic lines of flux of the pole pieces.

A

Armature reaction

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15
Q

What are interpoles?

A

Small pole pieces located between the main field poles and connected in series with the armature.

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16
Q

What procedure can be used to set the brushes to the neutral plane position in a DC machine?

A
  • Apply AC to the armature
  • Connect an AC voltmeter across the shunt field leads
  • Adjust brushes until the meter indicates 0 V
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17
Q

The DC motor known as a “constant speed motor” is the ______ motor.

A

Shunt

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18
Q

What type of motor should never be operated under a no-load condition?

A

Series

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19
Q

What determines the speed regulation of a DC motor?

A

Armature resistance

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20
Q

What is the method for reversing the direction of rotation for a DC motor?

A

Reverse the connection of the armature leads (or the field leads)

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21
Q

When a motor is connected differential compound, the ______ determines the direction of rotation of the motor at no load or light load.

A

Shunt field

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22
Q

In a compound DC motor control circuit, the field loss relay will disconnect the ______ if the power is lost in the ______.

A

armature, shunt field

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23
Q

The rotating part of an alternator is called the ______.

A

Rotor

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24
Q

The non-rotating part of an alternator is called the ______.

A

Stator

25
Q

In an alternator, what does the rotor do and what does it produce?

A
  • Provides the magnetism needed to induce voltage into the stator windings
  • Connects to some source of external DC to excite the alternator
26
Q

Connections to the armature of an alternator is normally done by using ______.

A

Sliprings

27
Q

An alternator containing eight poles per phase is turning at 900 RPM. What is the output frequency?

A

f = PS/120

f = (8)(900)/120

f = 60 Hz

28
Q

In an alternator, using a ______ is one method of preventing induced voltage from becoming excessive.

A

Field discharge resistor

29
Q

What are the three factors that determine output voltage of an alternator?

A
  • Strength of magnetic field of the rotor
  • Speed of rotation of the rotor
  • # of turns of wire in armature
30
Q

What must be done to a synchronous motor to make it have a leading power factor?

A

Overexcitation of the rotor

31
Q

Why should a synchronous motor never be started with DC?

A

It won’t start

32
Q

What are 5 characteristics of a synchronous motor?

A
  • Not an induction motor
  • Must have DC excitation
  • Operates at constant speed from full load to no load
  • Operates at synchronous speed
  • Has the ability to correct its own power factor
33
Q

What are amortissuer windings in a three phase synchronous motor?

A

Squirrel cage bars used to start the motor

34
Q

A three-phase motor has three slip rings on its rotor shaft. What type of motor is this?

A

Wound rotor motor

35
Q

What is the formula to calculate percent slippage?

A

Percent slip = (SynchSpeed-RotorSpeed) / SynchSpeed x 100

36
Q

What three things determine the amount of torque produced by an induction motor?

A
  • Phase angle difference between rotor and stator fields
  • Strength of magnetic field of the rotor
  • Strength of magnetic field of the stator
37
Q

What is synchronous speed?

A

The speed of the rotating magnetic field

38
Q

What two factors determine synchronous speed of a three-phase motor?

A
  • Number of stator poles per phase

- Frequency of the applied voltage

39
Q

What are the three major types of three-phase motors?

A
  • Squirrel cage induction
  • Wound rotor motor
  • Synchronous motor
40
Q

What is the operating principle of all three-phase motor?

A

Rotating magnetic field

41
Q

What is a motor?

A

A device that converts electrical energy into mechanical energy

42
Q

How do you reverse the direction of rotation of a three-phase motor?

A

Switch any two leads

43
Q

The wound rotor motor is popular in industry because it has ______ starting torque and ______ starting current.

A

High, low

44
Q

In a DC motor, what determines torque?

A
  • Strength of magnetic field of the pole pieces

- Strength of magnetic field of the armature

45
Q

What factors determine CEMF in a DC motor?

A
  • Strength of magnetic field of the pole pieces
  • Speed of rotation of the armature
  • # of turns of wire in armature
46
Q

What are the three major types of single-phase split-phase motors?

A
  • Resistance-start induction-run
  • Capacitor-start induction-run
  • Capacitor-start capacitor-run
47
Q

What are the two separate windings in split-phase motors?

A

Run windings and start windings

48
Q

In a split-phase motor, the ______ winding is made of many turns of small wire and is located at the top of the stator core.

A

Start

49
Q

In a split-phase motor, the ______ winding is made of few turns of large wire and is located at the bottom of the stator core.

A

Run

50
Q

Motors that are hermetically sealed use what to disconnect from the start winding?

A

Centrifugal switch

51
Q

The capacitor-start induction-run motor has a(n) ______ connected in series with the centrifugal switch and start windings.

A

AC electrolytic capacitor

52
Q

What is special about the capacitor-start capacitor-run motor?

A

The start windings remain energized

53
Q

In multi-speed fan motors, what permits the motor to be operated without damage?

A

High impedance of the stator windings

54
Q

What type of single-phase motor will operate on AC or DC voltage?

A

Universal motor

55
Q

Similar to DC series motor, the universal motor has the same construction but also has…

A

Compensating windings (conductive compensation and inductive compensation)

56
Q

Speed regulation of a universal motor is ______.

A

very poor

57
Q

What are the advantages of a wound rotor motor over a squirrel cage motor?

A
  • High starting torque and low current

- Speed control

58
Q

What is the principle of operation of a wound rotor motor?

A

Rotating magnetic field

59
Q

What is the principle of operation of a squirrel cage motor?

A

Induction

Motors & Generators (1 decks)

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