Deck 35: Harmonics and their Effects on Electrical Systems

Question 1

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) no
B) moderate
C) extreme

Answer 1

C

Question 2

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

A) 120 hertz
B) 180 hertz
C) 240 hertz
D) 300 hertz

Answer 2

C

Question 3

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

Answer 3

opposite

Question 4

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

Question 5

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

Question 6

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

A) true­RMS ammeter
B) harmonic analyzer
C) average ammeter
D) harmonic meter

Question 7

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

Question 8

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

A) name
B) frequency
C) sequence
D) magnitude

Question 9

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

Question 10

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

A) negative
B) positive
C) zero

Question 11

Harmonic problems generally involve of the transformer.

Question 12

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.

Question 13

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

A) name
B) frequency
C) sequence
D) magnitude

Question 14

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

A) triac light dimmer
B) lamp with an incandescent bulb
C) single-speed motor
D) heater

Question 15

Harmonics are classified by name, frequency, and sequence.

Question 16

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.

Question 17

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.

A) no
B) moderate
C) extreme

Question 18

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.

Question 19

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

A) pulsations
B) loads
C) phases
D) harmonics

Question 20

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