# Motors Book - Chapter 3

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• 1.

### The rotor in a AC alternator may also be called a(n) ___, even though the term "rotor" is more correct.

• A.

Drum switch

• B.

Brush

• C.

Stator

• D.

Armature

D. Armature
Explanation
The rotor in an AC alternator is sometimes referred to as an armature, although the term "rotor" is more technically accurate. The armature is the rotating component of the alternator that carries the current and generates the magnetic field necessary for power generation. It is responsible for converting mechanical energy into electrical energy. The term "armature" is often used in electrical engineering to describe the rotating part of a machine that interacts with the magnetic field.

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• 2.

### The most common alternator design consists of a stator in which the potential is induced by the rotating field supplied by the ___.

• A.

3-phase source

• B.

Exciter generator

• C.

Slip rings

• D.

Brushes

D. Brushes
Explanation
The correct answer is brushes. In the most common alternator design, the potential is induced in the stator by the rotating field supplied by the brushes. The brushes make contact with the rotating part of the alternator, known as the rotor, and allow the electrical current to flow between the stator and the rotor. This interaction between the brushes and the rotor creates the rotating magnetic field that induces the potential in the stator windings.

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• 3.

### In a common alternator design, ___ is applied to the rotor to move the rotor windings and their magnetic fields past the stator windings.

• A.

Torque

• B.

Electromagnetism

• C.

Voltage

• D.

Current

A. Torque
Explanation
In a common alternator design, torque is applied to the rotor to move the rotor windings and their magnetic fields past the stator windings. Torque is a rotational force that causes the rotor to spin, and this movement generates the necessary electromagnetic induction in the stator windings to produce voltage and current. Without the application of torque, there would be no movement and therefore no generation of electrical energy.

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• 4.

### A(n) ___ alternator is an alternator where a magnetic field is created in the rotor, which turns within the fixed stator windings, and AC power is supplied through the stator windings.

• A.

Excitor

• B.

Revolving-rotor

• C.

Revolving-field

• D.

All of the above

C. Revolving-field
Explanation
In a revolving-field alternator, the magnetic field is created in the rotor, which rotates within the fixed stator windings. This rotation of the rotor causes the magnetic field to revolve around the stator windings, inducing an alternating current (AC) power output. Therefore, the correct answer is revolving-field.

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• 5.

### A factor controlling the output voltage of an alternator is the ___.

• A.

Length of wire

• B.

Speed of the rotor

• C.

Strength of the magnetic field

• D.

All of the above

D. All of the above
Explanation
The output voltage of an alternator is controlled by multiple factors, including the length of wire, the speed of the rotor, and the strength of the magnetic field. The length of wire affects the resistance and impedance of the alternator, which in turn affects the output voltage. The speed of the rotor determines the frequency of the alternator's output voltage. Finally, the strength of the magnetic field influences the amplitude of the output voltage. Therefore, all of these factors play a role in controlling the output voltage of an alternator.

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• 6.

### A(n) ___ is used to control the main alternator voltage.

• A.

Voltage rating

• B.

Voltage regulator

• C.

Enclosure

• D.

Magnetic field

B. Voltage regulator
Explanation
A voltage regulator is used to control the main alternator voltage. It regulates the voltage output of the alternator to ensure that it remains within a specified range. This is important because excessive voltage can damage electrical components, while insufficient voltage can lead to poor performance or failure of electrical systems. The voltage regulator continuously monitors the alternator's output and adjusts it as needed to maintain a stable and appropriate voltage level.

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• 7.

### A ___ alternator consists of a stationary magnet and a single winding that is rotated in the field.

• A.

Single-phase AC

• B.

Single-phase DC

• C.

Three-phase AC

• D.

Three-phase DC

A. Single-pHase AC
Explanation
A single-phase AC alternator consists of a stationary magnet and a single winding that is rotated in the field. This means that the alternator generates alternating current (AC) with a single phase. Single-phase AC is commonly used in residential and small commercial applications where the power demand is relatively low. It is not as efficient or powerful as three-phase AC, but it is sufficient for many everyday electrical needs.

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• 8.

### A ___ is a power source used to create relative motion between a coil and a magnetic field.

• A.

Solid-state starter

• B.

Manual starter

• C.

Prime mover

• D.

Commutator

C. Prime mover
Explanation
A prime mover is a power source that is used to create relative motion between a coil and a magnetic field. It is responsible for initiating the movement and generating the necessary power for the coil to interact with the magnetic field. The other options, such as solid-state starter, manual starter, and commutator, do not fulfill the role of creating relative motion between a coil and a magnetic field.

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• 9.

### Alternators are rated in ___ at a standard power factor of 80%

• A.

Kilovolt amperes (kVA)

• B.

Kilowatts (kW)

• C.

Megawatts (MW)

• D.

None of the above

B. Kilowatts (kW)
Explanation
Alternators are rated in kilowatts (kW) at a standard power factor of 80%. This means that the rating of the alternator is given in terms of the actual power output in kilowatts, taking into account the power factor. The power factor is a measure of how effectively the alternator converts the input power into useful output power. By rating the alternator in kilowatts, it provides a more accurate representation of the actual usable power that the alternator can deliver at the given power factor.

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• 10.

### Alternators are placed in parallel to ___.

• A.

• B.

Enhance reliability by having multiple alternators in operation

• C.

Provide power during maintenance of other alternators

• D.

All of the above

D. All of the above
Explanation
Alternators are placed in parallel to carry added load when needed, enhance reliability by having multiple alternators in operation, and provide power during maintenance of other alternators. When there is a high demand for electricity, additional alternators can be connected in parallel to share the load and prevent overloading. Having multiple alternators in operation also increases reliability as if one alternator fails, the others can continue to supply power. Additionally, when one alternator is undergoing maintenance or repairs, the remaining alternators can provide power to ensure uninterrupted electricity supply. Therefore, all of the above options are correct.

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• 11.

### A ___ can be used to help match the frequency and phase of an alternator to the busbar, or to match two alternators

• A.

Synchroscope

• B.

Synchronous speed monitor

• C.

• D.

Slip ring

A. Synchroscope
Explanation
A synchroscope is a device that can be used to help match the frequency and phase of an alternator to the busbar, or to match two alternators. It provides a visual indication of the phase difference between the voltage of the alternator and the busbar. By observing the synchroscope, operators can adjust the speed or phase of the alternator to ensure synchronization with the busbar or with another alternator. This helps to prevent any damage or instability that could occur if the alternators are not properly synchronized.

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• 12.

### A(n) ___ energizes a relay and closes a contact when the incoming source and the busbar match.

• A.

Autotransformer starter

• B.

Automatic synchronizer

• C.

Field winding

• D.

All of the above

B. Automatic synchronizer
Explanation
An automatic synchronizer is a device that energizes a relay and closes a contact when the incoming source and the busbar match. This ensures that the two sources are synchronized before they are connected together. Therefore, an automatic synchronizer is the correct answer as it fulfills the given requirement.

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• 13.

### A ___ is the fixed unmoving part of a generator, consisting of a core and windings, that converts the energy of a magnetic field to electrical energy.

• A.

Brush

• B.

Rotor

• C.

Stator

• D.

Generator

C. Stator
Explanation
The stator is the fixed part of a generator that includes a core and windings. It converts the energy of a magnetic field into electrical energy.

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• 14.

### A(n) ___ generator is an assembly consisting of a small three-phase alternator used to supply current to an alternator rotor.

• A.

Revolving-rotor

• B.

Revolving-field

• C.

Brushless

• D.

Exciter

D. Exciter
Explanation
An exciter generator is an assembly consisting of a small three-phase alternator used to supply current to an alternator rotor. It is responsible for providing the initial electrical power needed to start the main generator and maintain its field current during operation. This allows the alternator rotor to produce a magnetic field and generate electricity.

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• 15.

### ___ is turning or twisting force that causes an object to rotate.

• A.

Electromagnetism

• B.

Magnetism

• C.

Torque

• D.

Friction

C. Torque
Explanation
Torque is the correct answer because it refers to the turning or twisting force that causes an object to rotate. It is a measure of the force's effectiveness in causing rotation and depends on both the magnitude and direction of the force applied. Electromagnetism and magnetism are not directly related to the concept of torque, while friction refers to the resistance encountered when two surfaces slide against each other, which is different from the concept of torque.

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• Current Version
• Mar 21, 2023
Quiz Edited by
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• Dec 18, 2012
Quiz Created by
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