Question 1

What steps should you follow when determining whether there are harmonic problems in single-phase systems?

Accepted Answer

There are several steps that can be foll...

Question 2

THDF stands for ____.

Accepted Answer

A)   triplen harmonic derating factor
B)   triplen harmonic desensitizing field
C)   transformer honed resultant field
D)   transformer harmonic derating factorE) A) and C)
F) B) and C)

Question 3

Harmonics are produced by loads that draw current in ____.

Accepted Answer

A)   a sine wave
B)   a linear manner
C)   a continuous manner
D)   pulsesE) A) and C)
F) B) and C) D

Question 4

Harmonics are voltages or currents that operate at a frequency that is ____ the fundamental power frequency.

Accepted Answer

A)   a multiple of
B)   a divisor of
C)   double
D)   within 10 Hz ofE) B) and C)
F) A) and B)

Question 5

A ____ is used to smooth the pulsations caused by a bridge rectifier.

Accepted Answer

A)   phasor
B)   filter capacitor
C)   transistor
D)   diodeE) B) and D)
F) B) and C)

Question 6

One way to deal with harmonic problems is to install a ____ neutral conductor.

Accepted Answer

A)   larger
B)   smaller
C)   common
D)   triplenE) None of the above
F) A) and D)

Question 7

To minimize interference, communication cables are run as close to the ____ conductor as possible.

Accepted Answer

A)   positive phase
B)   negative phase
C)   triplen
D)   neutralE) B) and C)
F) None of the above

Question 8

The most accurate method for determining whether there is a harmonics problem is to use a(n)  ____.

Accepted Answer

A)   transformer
B)   average value ammeter
C)   true rms ammeter
D)   harmonic analyzerE) A) and B)
F) A) and C)

Question 9

Transformers are typically designed for ____-hertz operation.

Accepted Answer

A)   50
B)   60
C)   100
D)   120E) All of the above
F) B) and D)

Question 10

Harmonics called ____ have a zero sequence.

Accepted Answer

A)   positives
B)   negatives
C)   doublens
D)   triplensE) C) and D)
F) B) and C)

Question 11

The instantaneous peak value of current is equal to the rms value multiplied by ____.

Accepted Answer

A)   0.651
B)   1.111
C)   1.414
D)   1.730E) All of the above
F) B) and C)

Question 12

Harmonic currents in the neutral conductor induce ____ currents into the communication cable.

Accepted Answer

A)   high-frequency
B)   low-frequency
C)   no new
D)   constantE) All of the above
F) B) and C)

Question 13

What problems are caused by harmonics in circuit breakers?

Accepted Answer

Thermomagnetic circuit breakers use a bi...

Question 14

What problems do triplens pose for neutral bus ducts?

Accepted Answer

Triplen harmonic currents can also cause problems with neutral bus ducts and connecting lugs. A neutral bus is sized to carry the rated phase current. Since triplen harmonics can cause the neutral current to be higher than the phase current, it is possible for the neutral bus to become overloaded. Electrical panelboards and bus ducts are designed to carry currents that operate at 60 hertz. Harmonic currents produce magnetic fields that operate at higher frequencies. If these fields should become mechanically resonant with the panelboard or bus duct enclosures, the panelboards and bus ducts can vibrate and produce buzzing sounds at the harmonic frequency.

Question 15

How are harmonics classified?

Accepted Answer

Harmonics are classified by name, frequency, and sequence. The name refers to whether the harmonic is the second, third, fourth, and so on, of the fundamental frequency. The frequency refers to the operating frequency of the harmonic. The second harmonic operates at 120 hertz, the third at 180 hertz, the fourth at 240 hertz, and so on. The sequence refers to the phasor rotation with respect to the fundamental waveform. In an induction motor, a positive sequence harmonic would rotate in the same direction as the fundamental frequency. A negative sequence harmonic would rotate in the opposite direction of the fundamental frequency. Harmonics called triplens have a zero sequence. Triplens are the odd multiples of the third harmonic (3rd, 9th, 15th, 21st, and so on).

Question 16

Ammeters that respond to the average value convert the alternating current into direct current. This value must be increased by a factor of ____ to change the average reading into the rms value for a sine wave current.

Accepted Answer

A)   0.651
B)   1.111
C)   1.414
D)   1.730E) A) and C)
F) A) and B)

Question 17

The phasor rotation of a negative harmonic causes an induction motor to produce ____.

Accepted Answer

A)   positive feedback
B)   a high magnetic field
C)   less torque
D)   more torqueE) All of the above
F) A) and B)

Question 18

What are some devices that are responsible for harmonics?

Accepted Answer

Harmonics on single-phase power lines ar...

Question 19

It is necessary to use an ammeter that responds to ____ current when making a check for harmonics.

Accepted Answer

A)   single-phase
B)   rectified
C)   true rms
D)   averageE) A) and C)
F) All of the above

Question 20

A ratio of ____ between measurements made with a true rms ammeter and an average value ammeter indicates no harmonic distortion.

Accepted Answer

A)   0.5
B)   0.75
C)   0.833
D)   1.0E) B) and C)
F) A) and D)

Exam 20: Harmonics

What steps should you follow when determining whether there are harmonic problems in single-phase systems?

Correct Answer
verified
There are several steps that can be foll...
View Answer

THDF stands for ____.

Correct Answer
verified

Harmonics are produced by loads that draw current in ____.

Correct Answer
verified
D

Harmonics are voltages or currents that operate at a frequency that is ____ the fundamental power frequency.

Correct Answer
verified

A ____ is used to smooth the pulsations caused by a bridge rectifier.

Correct Answer
verified

One way to deal with harmonic problems is to install a ____ neutral conductor.

Correct Answer
verified

To minimize interference, communication cables are run as close to the ____ conductor as possible.

Correct Answer
verified

The most accurate method for determining whether there is a harmonics problem is to use a(n) ____.

Correct Answer
verified

Transformers are typically designed for ____-hertz operation.

Correct Answer
verified

Harmonics called ____ have a zero sequence.

Correct Answer
verified

The instantaneous peak value of current is equal to the rms value multiplied by ____.

Correct Answer
verified

Harmonic currents in the neutral conductor induce ____ currents into the communication cable.

Correct Answer
verified

What problems are caused by harmonics in circuit breakers?

Correct Answer
verified
Thermomagnetic circuit breakers use a bi...
View Answer

What problems do triplens pose for neutral bus ducts?

How are harmonics classified?

Ammeters that respond to the average value convert the alternating current into direct current. This value must be increased by a factor of ____ to change the average reading into the rms value for a sine wave current.

Correct Answer
verified

The phasor rotation of a negative harmonic causes an induction motor to produce ____.

Correct Answer
verified

What are some devices that are responsible for harmonics?

Correct Answer
verified
Harmonics on single-phase power lines ar...
View Answer

It is necessary to use an ammeter that responds to ____ current when making a check for harmonics.

Correct Answer
verified

A ratio of ____ between measurements made with a true rms ammeter and an average value ammeter indicates no harmonic distortion.

Correct Answer
verified

Exam 20: Harmonics

What steps should you follow when determining whether there are harmonic problems in single-phase systems?

Correct AnswerverifiedThere are several steps that can be foll...View AnswerShow Answer

THDF stands for ____.

Correct AnswerverifiedShow Answer

Harmonics are produced by loads that draw current in ____.

Correct AnswerverifiedD

Harmonics are voltages or currents that operate at a frequency that is ____ the fundamental power frequency.

Correct AnswerverifiedShow Answer

A ____ is used to smooth the pulsations caused by a bridge rectifier.

Correct AnswerverifiedShow Answer

One way to deal with harmonic problems is to install a ____ neutral conductor.

Correct AnswerverifiedShow Answer

To minimize interference, communication cables are run as close to the ____ conductor as possible.

Correct AnswerverifiedShow Answer

The most accurate method for determining whether there is a harmonics problem is to use a(n) ____.

Correct AnswerverifiedShow Answer

Transformers are typically designed for ____-hertz operation.

Correct AnswerverifiedShow Answer

Harmonics called ____ have a zero sequence.

Correct AnswerverifiedShow Answer

The instantaneous peak value of current is equal to the rms value multiplied by ____.

Correct AnswerverifiedShow Answer

Harmonic currents in the neutral conductor induce ____ currents into the communication cable.

Correct AnswerverifiedShow Answer

What problems are caused by harmonics in circuit breakers?

Correct AnswerverifiedThermomagnetic circuit breakers use a bi...View AnswerShow Answer

What problems do triplens pose for neutral bus ducts?

How are harmonics classified?

Ammeters that respond to the average value convert the alternating current into direct current. This value must be increased by a factor of ____ to change the average reading into the rms value for a sine wave current.

Correct AnswerverifiedShow Answer

The phasor rotation of a negative harmonic causes an induction motor to produce ____.

Correct AnswerverifiedShow Answer

What are some devices that are responsible for harmonics?

Correct AnswerverifiedHarmonics on single-phase power lines ar...View AnswerShow Answer

It is necessary to use an ammeter that responds to ____ current when making a check for harmonics.

Correct AnswerverifiedShow Answer

A ratio of ____ between measurements made with a true rms ammeter and an average value ammeter indicates no harmonic distortion.

Correct AnswerverifiedShow Answer

Correct Answer
verified
There are several steps that can be foll...
View Answer

Correct Answer
verified

Correct Answer
verified
D

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
Thermomagnetic circuit breakers use a bi...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
Harmonics on single-phase power lines ar...
View Answer

Correct Answer
verified

Correct Answer
verified