Deck 35: Harmonics

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

​The odd multiples of the third harmonic (third, ninth, fifteenth, twenty-first, etc.) are called _______________.

Answer 2

triplens

Question 3

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

A) ​negative
B) ​positive
C) ​zero

Answer 3

C

Question 4

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 5

​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

Question 6

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

Question 7

​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 8

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 9

​ Harmonics are classified  by name, frequency, and sequence.

Question 10

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

A) ​true-RMS ammeter
B) harmonic analyzer​
C) ​average ammeter
D) ​harmonic meter

Question 11

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

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

Question 12

To test for harmonic distortion in a three-phase four-wire system, measure all phase currents and the _______________ current with both a true-RMS indicating ammeter and an average-indicating ammeter.​

Question 13

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 14

​Harmonic problems generally involve _______________ of the transformer.

Question 15

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 16

A negative-sequence harmonic would rotate in the _______________ direction of the fundamental frequency​.

Question 17

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 18

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

Question 19

​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 20

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