AC Theory 3 Part 5,6 & 7
In a 3-phase generator, the three sets of windings are placed ? apart.
120 degrees 7Q5
4Q38 Ac three pic Fundamental signal peak voltage is ? V.
20
A ? solid-state switch draws operating current directly from a power source and does not allow the operating current to flow through the load.
3-wire 4Q35
4Q59 How many degrees out of phase are Input 1 and Input 2 on Display Screen 1?
90 degrees 4q59
What is the approximate root mean square value of Waveform 2 in Display 3? 4Q62
Approx. 4.24 A 4Q68
What is the function of pole pieces installed in the generator housing?
To help concentrate the magnetic field . 6Q19
The reason the current peak value in Display 2 is not equal to approximately 1.41 times the rms measured value is because the waveform is not a pure sine wave. 4Q62
True
The higher the carrier frequency to an AC motor, the closer the output sine wave is to a pure fundamental frequency sine wave and the cooler the motor operates.
True 4Q15
In a transistor, a very small current applied to one lead controls a large current flow through the other two leads.
True 4Q26
When a conductor cuts magnetic flux lines, a voltage is induced into the conductor.
True 6Q2
Permanent magnets are used sometimes as the field poles in small generators.
True 6Q21
DC generators operate on the principle of electromagnetic induction.
True 6Q3
How is object vibration related to the type of sound produced by the object?
a. High frequencies produce high, shrill sounds that vibrate at several thousand vibrations per second. b. Low frequencies produce deep, bass sounds that vibrate at several hundred vibrations per second. c. The faster an object vibrates, the higher the frequency produced. d. The slower an object vibrates, the lower the frequency produced. 4Q20
? is the process of taking a small signal and increasing the size of the signal.
amplification 4Q27
5Q4pic What letter matches the... Magnetic field poles
A 5Q4
What is the approximate root mean square value of Waveform 1 in Display 3? 4Q62
c. Based on approximately 250 V peak voltage, approximately 177 V rms 4q67
A(n) ? is an acoustical unit used to measure the intensity (volume) of sound.
decibel 4Q22
Almost all power losses in a generator, with the exception of flux linkage, are manifested in the form of ? .
heat 6Q43
The volts/division (volts per division) control selects the ? of the displayed waveform.
height 4Q10
State of Output L6 is ? . 4q54
high
49Determine whether the output state is high or low, based on the input states and the logic functions in the illustrations. State of ouput L_2_ is ?
high 4q50
What is the problem associated with increasing carrier frequency of a variable frequency drive?
it can increase the noise produced by the motor.
4q52 Determine whether the output state is high or low, based on the input states and the logic functions in the illustrations. State of Output L4 is ? .
low 4q52
A series generator is self-excited with residual ? .
magnetism 6Q27
The shunt type of generator provides ? output voltage before the load is applied.
maximum 6Q32
A generator is a device that converts ? energy into ? energy.
mechanical / electrical 6Q1
4Q38 ac three pic Fundamental signal period is ? seconds
.008
In Display 1, the meter tells the time between the two cursors. What is time per division control setting (sec/div) of the meter? 4Q62
.5 sec / div
4Q38 ac three pic Fundamental signal frequency is ? Hz.
125
A 4-pole generator will be supplying several loads that are designed for 60 hertz. At what speed does the generator need to be driven?
1800 RPM S = 120 * F / # of poles S = 120 * 60 / 4 S = 1,800 RPM
4q58 If Input 1 on Display Screen 2 is 60 Hz, what is the frequency of Input 2?
180hz
4Q38 ac three pic Carrier signal frequency is ? kHz.
5.25 F_CARR_ = Pulses * F_FUND_ = 125 * 42 =5.25 kHz 4Q43
4Q36 AC Three pic Identify the letter desisnation for... positive alteration
B
4Q36 AC Three pic Identify the letter desisnation for... Time
C
4Q36 AC Three pic Identify the letter desisnation for... Negative alternation
D
4q58 What type of voltage is Display 3 showing?
DC voltage
4Q36 AC Three pic Identify the letter desisnation for... One cycle
E
4Q36 AC Three pic Identify the letter desisnation for... Voltage / current
F
The voltage limit of an oscilloscope equals 1/10th the normal rated voltage when a 10x probe is used.
False 4Q11 Note: The voltage limit of an oscilloscope equals 10 times the normal rated voltage when a 10x probe is used.
Operating current is the minimum current that ensures proper operation of a solid-state switch.
False 4Q33 Note: Minimum holding current is the minimum current that ensures proper operation of a solid-state switch.
When AC voltage is generated and then converted to DC voltage by use of a commutator, the voltage output is constant.
False Note: The voltage is a pulsating DC voltage and is more commonly referred to as ripple voltage. 6Q11
? is the number of cycles per second of an AC sine wave.
Frequency 4Q1
A two-wire solid-state switch is also called a load-powered switch because the switch draws operating current from the power source and allows the operating current to return to the power source through the load.
True 4Q32
The higher the sample rate of an oscilloscope, the more accurate the trace of the signal being tested.
True 4Q6
Generators are electromechanical devices that turn ? energy into ? energy.
Mechanical / electrical 5Q1
To generate 50 hertz with an 8-pole generator, the speed of rotation must be ? revolutions per minute.
S = f * 120 / P S = 50 * 120 / 8 S = 750 RPM 7q21
Pole faces that jut out and are very pronounced are called ? poles.
Salient 7Q11
Alternators with small kilovolt-ampere ratings are usually ? cooled.
air 7q15
4Q62 In Display 1, Cursor 1 is set to measure the inrush current at the start of a motor. What is the peak starting current of the motor?
approximately 48 A
4q58 What is the root mean square voltage of Input 1 on Display Screen 1 when the volts/div setting is on 50?
c. Based on approximately 175 V peak voltage, approximately 124 V rms `
? is the frequency that controls the number of times the solid-state switches in the inverter section of a Pulse Width Modulated (PWM) variable frequency drive turn on and turn off per second.
carrier frequency 4Q14
Digital circuits fail because the ? is lost somewhere between the circuit input and output stages.
digital signal 4Q24
The DC voltage and current that is supplied to the field of a generator is called the ? power.
exciter 5Q19
The abbreviation PMG stands for a type of generator that uses ? for the flux field.
permanent magnets 5Q17
46Determine whether the following NPN transistor is good, shorted, or open, based on the ohmmeter readings in the illustration. The solid probe leads represent the first reading. The dashed probe leads represent the second reading. Transistor 2 is ?
shorted
4Q38 ac three pic Number of carrier signal pulses per fundamental signal cycle is ? .
42
4Q36 AC Three pic Identify the letter desisnation for... Periods
A
4Q37 AC three pic Idendify the letter designation for... Fundamental Signal
A
In Display 2, what is the approximate peak current value? 4Q62
Approximately 50 A
4Q37 AC three pic Idendify the letter designation for... Waveform
C
? typically output sine waves, square waves, or triangular waves.
Signal generator 4Q18
A ? is a thyristor that is triggered into conduction in only one direction and is suited for DC current use.
Silicon Controlled Rectifier (SCR) 4Q28
4Q37 AC three pic Idendify the letter designation for... Pulses
D
In which two ways can a transistor be used? I. Amplifier II. Receiver III. Switch IV. Transmitter
I. and III. 4Q25
Air-cooled alternators usually have a ? attached to one end of the rotor to help circulate air.
fan 7Q16
The series field windings are made up of ? turns with large wire, and the leads are labeled ? and ? .
few / s1 / S2 6Q23
Manually operated switches include ? .
foot switches 4Q31
Large-capacity generators are often enclosed in a(n) ? atmosphere for cooling purposes.
hydrogen 7Q17
State of Output L7 is ? .
low 4q55
46Determine whether the following NPN transistor is good, shorted, or open, based on the ohmmeter readings in the illustration. The solid probe leads represent the first reading. The dashed probe leads represent the second reading. Transistor 1 is ?
open
4Q37 AC three pic Idendify the letter designation for... Carrier Signal
B
Meters designed to operate on circuits with solid-state devices include a bypass filter circuit to separate the power frequency from the ? frequency and display only the power frequency.
Carrier 4Q5
4Q48 pics of a, b and c which is .... temporary loss of signal Voltage amplitude change voltage frequency change
a = temporay loss of signal b = voltage amplitude change c = voltage frequency change.
0f 45 pic a b & c which is... voltage w/ clipped wave (flat topping) signal gain voltage with DC offset (DC in signal)
a = voltage with DC offset (DC in signal) b = signal gain c = Voltage with clipped wave (flat topping)
A cycle is one complete wave of alternating positive and negative voltage or current. A(n) ? is one half of a cycle.
alternation 4Q2
4Q62 In Display 1, Cursor 2 is set to measure the running current of the motor. What is the running current (peak) of the motor?
approximately 10 A
The winding in a generator where voltage is induced is called the ? .
armature 5Q8
What is the name of the rotating member of the DC generator?
armature 6Q13
Series generators would be best used with a ? load.
constant 6Q30
A ? is a special test instrument (DC voltmeter) that detects the presence or absence of a high or low signal.
digital logic probe 4Q23
A(n) ? oscilloscope is an oscilloscope that displays two signal traces simultaneously.
dual trace 4Q9
In a flat compound generator, the load voltage is ? the no-load voltage.
equal to 6Q39
46Determine whether the following NPN transistor is good, shorted, or open, based on the ohmmeter readings in the illustration. The solid probe leads represent the first reading. The dashed probe leads represent the second reading. Transistor 3 is ?
good
A ? -shunt compound generator has the shunt fiel in parallel with the series winding and the armature.
long 6Q37
Determine whether the output state is high or low, based on the input states and the logic functions in the illustrations. 4q51 State of Output L5 is ? .
low 4q53
State of Output L8 is ? . 4q56
low 4q56
Triacs should be tested under operating conditions using a(n) ? .
oscilloscope 4Q30
? bandwidth is the highest frequency an oscilloscope can capture in a single pass.
real-time 4Q7
The ? rotor uses a smooth, longer, and narrower construction to minimize wind resistance and centrifugal forces.
round 7Q12
? turn-on is a method of turning on a thyristor that occurs when a fast-rising voltage is applied across the terminals of a triac.
static 4Q29
The revolving field AC generator has the armature windings positioned around the generator housing. The name given to the armature in this case is called the ? .
stator 5Q16
4Q38 ac three pic Fundamental signal RMS voltage is...?
14.14 V
A single coil generator spinning in a magnetic field will produce a full sine wave for every ? of rotation.
360 degrees 5Q9
An AC motor designed to operate at 60 hertz rotates more slowly when the frequency is less than 60 hertz and rotates faster when the frequency is above 60 hertz.
True 4Q4
Increasing the speed of rotation or increasing the flux field strength are both ways to increase the output voltage of a generator without making physical changes to the machine.
True 5Q14
A rotating field AC generator is connected to the DC voltage source through slip rings.
True 5Q18
To control the output voltage of a shunt generator, an electronic voltage regulator is installed to sense changes in the output voltage and makes adjustments to the shunt field current.
True 6Q34
Determine whether the output state is high or low, based on the input states and the logic functions in the illustrations. 4q51 State of Output L3 is ? .
high
State of Output L9 is ? . 4q57
high
49Determine whether the output state is high or low, based on the input states and the logic functions in the illustrations. State of ouput L_1_ is ?
high 4q49
The larger the amplitude of a sound wave, the ? the sound produced.
louder 4Q21
Two-wire solid-state switches connected in ? affect the operation of a load because of the voltage drop across the switches.
series 4Q34
On an oscilloscope, the horizontal (x) axis represents ? , and the vertical (y) axis represents ? of the voltage waveform.
time / amplitude 4Q8
To determine the frequency of the waveform, divide the ? into 1.
time period 4Q13
One full revolution of a 4-pole generator will result in ? cycle(s) of output.
two 5Q20
A frequency meter is a test instrument used to measure the frequency of a DC signal.
False 4Q3
Frequency meters graphically show any distortion present in the circuit voltage.
False Note: Frequency meters are typically used in applications where high accuracy and direct numerical frequency readout are required. Oscilloscopes graphically show any distortion present in the circuit voltage. 4Q12
Gain is the ratio of the amplitude of the input signal to the amplitude of the output signal.
False Note: Gain is the ratio of the amplitude of the output signal to the amplitude of the input signal. 4Q19
? is accomplished using test instruments to either measure an electronic signal already within a system or circuit or to measure an electronic signal intentionally injected into a system or circuit.
Signal tracing 4Q17
5Q4pic What letter matches the... Slip ring
C 5Q4
According to Fleming's generator rule, match the correct meaning of the extended digits in the figure. Center finger = ? Forefinger = ? Thumb = ?
Center finger = Direction of induced current Forefinger = Direction of flux field Thumb = Direction of thrust 6Q4
The magnetic neutral plane will shift in the direction of the field rotation.
False Note: The magnetic neutral plane will shift in the direction of the armature rotation. 6Q45
When using the Fleming left hand rule for generators, the thumb indicates the direction of thrust, the forefinger indicates the direction of field flux from N to S, and the center finger indicates the direction of induced current.
True 5Q5
? voltage is being produced when the rotating conductor is parallel to the magnetic flux lines.
Zero voltage 6Q5
Cumulative compounding is when the series and shunt fields ? each other in producing electromagnetic force.
aid 6Q38
The shunt field has a ? resistance because it is made of ? wire.
high / small 6Q25
Shunt field windings are connected in ? with the armature in a generator, and the leads are tagged ? and ? .
parallel / F1 / F2 6q24
? are constructed as a continuous ring, with each end of the armature loop connected to a separate ring.
slip rings 7Q4
When the armature is held stationary in a generator, it is called the ? .
stator 7Q9
A revolving armature AC generator has each end of the rotating loops or winding connected to what component(s)?
the slip rings 5Q13
There is no limit to the amount of power that can be generated with the revolving armature type of generator.
False Note: Brushes and slip rings can handle a limited level of voltage and kilovolt-ampere capacity. 7Q6
How many poles are required for a generator to have a frequency of 60 hertz at 1,200 revolutions per minute?
P = f * 120 / S P = 60 * 120 / 1,200 P = 6 poles 7Q22
Another method of paralleling two alternators is with the use of a synchroscope.
True 7Q29
The frequency of the pulsating DC output voltage of a generator is ? that of an AC generator. `
Twice Note: The frequency of output, for the pulsating DC is considered to be twice that of an AC generator because the commutator maintains "+" polarity throughout 360° of rotation, which provides two ripple pulses for one AC cycle. 6Q12
To prevent a shift in the neutral plane, ? windings are installed in the generator to cancel the effects of self-induction in the armature.
compensating, interpole and thomson-Ryan 6Q46
? loss is due to molecular friction.
hysteresis 6Q42
When a load is connected to a series generator, the output voltage ? .
increases 6Q26
There ? real advantage to using a rotating field and a stationary armature on commercial generators.
is a Note: This design permits higher voltage and kilovolt-ampere ratings because the outside circuit is connected directly to the stator and is not routed through slip rings and brushes. 7Q7
The ? is the rotating member of a generator or motor.
rotor 7Q8
The 3 are components that make up the armature. They are ?.
commutator iron core windings 6Q14
Compound generators overcome the voltage regulation problems of a series generator, providing good flexibility, voltage regulation, and load control.
True 6Q36
Exciters are made in ? ways including stationary and rotating.
a variety of7Q13
Maximum voltage is induced into a conductor when it cuts the magnetic field at ? .
90 degrees 6Q6
5Q4pic What letter matches the... Brush
D 5Q4
There are three types of armuture winding found in generators. They are ?
Frogleg Lap wound Wave wound 6Q15
In order to induce electrical energy into a conductor or generator, what three factors must be present? I. Conductor II. Heat III. Magnetic field IV. Relative motion V. Rotation
I III and IV.
Select the factors that determine the output voltage of an alternator. I. The length of the armature conductors II. The speed of rotation of the conductor in the magnetic field III. The strength of the magnetic field IV. The size of the conductor
I and II,. and III. 7Q24
Select the factors that determine the frequency of an alternator. I. Number of stator poles II. Voltage level III. Phase IV. Speed of rotation.
I and IV. 7Q19
There are two basic types of alternators. These are the revolving ? type and the revolving ? type.
armature / field 4Q3
To convert the AC voltage from the armature to DC voltage, DC generators make use of a(n) ? .
commutator 6Q9
As the load is increased on a shunt type generator, the output voltage will ? .
decrease 6Q33
Power loss due to induced currents in the core material of a generator is called ? loss.
eddy current 6q41
As additional loads are connected to a series generator, the output voltage will continue to ? until the iron in the pole pieces and armature becomes ? .
increase / saturated 6Q28
? wound armatures are used in machines designed for low voltage and high current.
lap 6Q17c
The source for mechanical motion supplied to a generator is referred to as the ? .
prime mover 5Q2
Self-excited shunt generators make use of ? to start the generation process.
residual magnetism 6Q31
Two types of rotating field construction are the ? pole rotor and the ? rotor.
salient , round 7Q10
When a conductor loop is continuously rotated in a magnetic field, the AC output voltage follows the ? function.
sine 6Q8
The rotating armature of an AC generator is connected to its external circuit through ? while a DC generator uses a(n) ? to make the connection.
slip rings / commutator 5Q7
The wires connected to the brushes of a generator are designated ? and ? .
A1 / A2 6Q16
When using the "three-lamp" method, how does an Electrical Worker know when the two alternators are in-phase with each other?
All three lamps will be off. 7Q28
? wound armatures are used in machines designed for high voltage and low current.
wave 6Q17b
5Q4pic What letter matches the... Armature windings or loops
B 5Q4
Which of the following statements are/is a reason brushes are usually made of carbon are: I. Carbon is softer than copper and allows the brushes rather than the commutator to wear (the latter being more difficult to repair). II. Carbon withstands the high temperatures that may be present because of arcing and friction. III. Carbon, copper, and moisture form a very thin, conductive film on the commutator that lubricates and reduces wear.
I., II., and III. 6Q18
Which of the factors listed determine the level of the output voltage of a series generator? I. Number of turns in the armature II. The strength of the magnetic field at the pole pieces III. The speed of the cutting action IV. The direction of rotation
I., II., and III. 6Q29
The ? -shunt compound generator has the shunt field connected in parallel with the armature.
Short 6Q37
The two primary magnetic flux fields in a generator are field flux and armature flux.
True 6Q44
If two DC generators are simply connected in parallel without an equalizer connection, one generator will take the load and the second generator will act as a DC motor, drawing current from the first generator.
True 6Q48
Another name for an AC generator is the alternator.
True 7Q1
If the number of turns of the coil is fixed by the generator's design, and speed of rotation is fixed by the output frequency requirements, the most practical option for voltage control is by increasing or decreasing the strength of the magnetic field of the rotor.
True 7Q25
Three conditions that must be met when connecting two 3-phase alternators in parallel are: I. Each generator must have the same frequency. II. The output voltages of the two machines must be equal. III. The phase rotation of the two machines must be the same. Phases A, B, and C of one machine must be in sequence with the same phase of the other machine.
True 7Q26
A common method of detecting when the direction of the magnetic field of one alternator is matched with the phase rotation of a paralleled alternator is with the use of three lights.
True 7Q27
A ? causes the AC voltage that is generated to appear as a DC voltage output, because it is a ring constructed of segments separated by insulating material. The connection of the generator loop to these segments is such that the output is always of the same polarity.
commutaor 6q10
The primary difference between a simple DC generator and a simple AC generator is the method by which the voltage is removed from the armature; in a DC generator, the voltage is removed by using brushes on ? . In an AC generator, the voltage is removed by using ? .
commutator / sliprings 7Q2
What is the formula for determining the frequency of alternator
f = P * S / 120 7Q20
A generator has four poles and a speed of 1,500 revolutions per minute. What is the output frequency?
f = S * P / 120 f = 1500 * 4 / 120 f = 50 Hz 7Q23
The measure of how frequently a generator produces a sine wave is called the ? of the waveform.
frequency 5Q10
? wound armatures are probably the most commonly used because they are designed for moderate voltages and moderate currents.
frogleg 6Q17a
In an over-compound generator, the load voltage is ? the no-load voltage.
greater than 6Q39
Which dissipates heat faster, hydrogen or air?
hydrogen 7q18
Increasing the turns or loops of wire on the rotating armature of a generator would cause a(n) ? output of the generator.
increase of voltage 5Q12
In an under-compound generator, the load voltage is ? the no-load voltage.
less than 6Q39
If there is an external circuit for current to flow, electron current will flow from the ? to the ? terminal in the circuit.
negative / positive Note: Be aware that this is the external circuit, and that internally to the generator it looks like current is flowing to the negative terminal. 5Q6
Differential compounding is when the series field windings ? the shunt field windings in the production of electromagnetic force.
oppose 6Q38
The greatest generator loss is due to the ? of the windings.
resistance 6q40
AC generators can be constructed in two basic styles and can be described as a ? type or a ? type generator.
revolving armature / revolving field 5Q11
When DC generators are connected in parallel, an equalizing connection is used to connect the ? fields of the two machines in ? with each other.
series / parallel 6Q47
Compound generators make use of a ? field winding and a ? field winding.
series / shunt 6 Q35
What are the two types of connections for generator field windings?
series and shunt 6q22
Once the pole pieces are mounted in the generator, the field windings are ? the pole pieces to form an electromagnet.
wound around. 6Q20
? voltage is induced into the conductor when the loop is at 0°, 180°, and 360° in relation to the field.
zero voltage 6Q7
