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Exam 35: Harmonics and their Effects on Electrical Systems

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Question 1

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When pulsating currents are connected to a three-phase four-wire system, triplen harmonic frequencies disrupt the normal phasor relationship of the phase currents and can cause the phase currents to add in the neutral conductor.

A) True
B) False

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Question 2

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The formula for determining the transformer harmonic derating factor produces a value somewhere between _____.

A) zero and one
B) zero and ten
C) zero and the RMS phase current
D) zero and the instantaneous peak value

E) A) and D)
F) A) and C)

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Question 3

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Because the phasor rotation of a negative harmonic is the same as that of the fundamental frequency, it will tend to weaken the rotating magnetic field of an induction motor causing it to produce much greater torque.

The odd multiples of the third harmonic (third, ninth, fifteenth, twenty­first, etc.) are called .

What are voltages or currents that operate at a frequency that is a multiple of the fundamental power frequency?

To minimize interference, telecommunication cables are run as close to phase conductors as possible and as far away from the neutral conductor as possible.

The of a harmonic refers to whether the harmonic is the second, third, fourth, or so on of the fundamental frequency.

A particular set of harmonics called "triplens" has a sequence.

Given a harmonic with a fundamental power frequency of 60 hertz, what would be the frequency of the fourth harmonic?

One method of determining harmonic problems on single-phase systems is to make two separate current checks. When this is performed, a ratio of average to true-RMS equal to one indicates harmonic distortion.

Harmonics are classified by name, frequency, and sequence.

To calculate the maximum load that should be placed on a transformer, the derating factor by the kilovolt-ampere capacity of the transformer.

Harmonic problems generally involve of the transformer.

The of a harmonic refers to the phasor rotation with respect to the fundamental waveform.

Harmonics on single-phase powerlines are generally caused by a device such as a .

Harmonics are produced by linear loads that draw current in a continuous manner.

One method of determining harmonic problems on single-phase systems is to make two separate current checks. When this is performed, a ratio of average to true-RMS equal to 0.5 indicates harmonic distortion.

A negative­sequence harmonic would rotate in the direction of the fundamental frequency.

To test for harmonic distortion in a three-phase four-wire system, measure all phase currents and the current with both a true­RMS indicating ammeter and an average­indicating ammeter.

What device should be used to determine the name, sequence, and amount of harmonic distortion?