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Transformers ch 6

Harmonics

QuestionAnswer
1. __is the order in which waveforms from each phase (A,B, and C) cross zero. (Current crest rotation; Harmonic sequence; Phasor rotation ; Harmonic degree) Phasor rotation
2. __ is the ratio of the current harmonics to the maximum current load. ( Displacement power factor; Distortion power factor; Total demand distortion; Total harmonic distortion) Total demand distortion
3. __ power is the power, in W or kW, used by motors,lights, and other devices to produce useful work ( Reactive; True; Total;Useful) True Power
4. The National Electrical Code requires neutral conductor overcurrent protection T/F False
5. __ power is the power, in VAR or kVAR, stored and released by inductors and capacitors. ( Apparent, Harmonic, Inductive, Reactive) Reactive
6. __ is the amount of harmonics on a line compared to the fundamental frequency of 60 Hz. (Displacement power factor, Distortion power factor, Total demand distortion, Total harmonic distortion) Total harmonic distortion
7. Flat-topping occurs when many loads draw current in pulses at the maximum voltage level and overload the power source T/F True
8. The __ is the peak value of a waveform divided by the rms value of the waveform. (Current crest factor; Displacement power factor; K-factor; Power factor) Current crest factor
9. A __ is a controller responsible for providing the initial startup voltage and maintaining constant current through a lamp. (Ballast; Harmonic filter; Lamp switch; Rectifier) Ballast
10. For an accurate measurement of the THD in a system, the THD should be measured at the harmonic-generating load. T/F False
11. Zero sequence harmonics do not produce a rotating field in either direction. T/F True
12. Only single-phase loads generate triplen harmonics. T/F True
13. A __ is a voltage or current at a frequency that is an integer multiple of the fundamental frequency. (Harmonic; Phase; Pulse; Waveform) Harmonic
14. Explain what the Fourier transform is and how it is used. mathematically decompose a waveform into its parts.
15. A __ uses capacitors and inductors that are tuned to remove particular harmonic frequencies. (Active harmonic filter; Harmonics mitigating transformer; K-rated transformer; Passive harmonic filter) Passive harmonic filter
16. Odd-numbered harmonics add together and increase their effect. T/F True
17. Postitive sequence harmonics have the same phase sequence as the third harmonic T/F False
18.__ is the ratio of real power to apparent power in a circuit or distribution system. (Displacement power factor, Distortion power factor; Harmonic power factor; Power factor) Power Factor
19. The neutral has two nonoverlapping current pulses for every single pulse on the line when one of the phases of a three-phase system has no load and the other two phases have nonlinear loads. T/F True
20. If two phases are at full load with no load on the third phase, the maximum neutral current can be evaluated in the same way as with balanced loads T/F True
21. K-rated transformers reduce harmonics. T/F False
22.A __ generally works by combining waveforms in ways where the positive part of one waveform adds to the negative part of another waveform, resulting in some degree of cancellation. ( next cARD)
(Active harmonic filter; Harmonics mitigating transformer; K-rated transformer; Passive harmonic filter)
23. Negative sequence transformers have the opposite phase sequence to the fundamental harmonic. T/F True
24. Zero sequence harmonics can add together. T/F True
25. A __ power supply is a power supply for electronic devices that includes an internal control circuit that quickly switches the load current ON and OFF in order to deliver a stable output voltage ( next card) Switched-mode
(Current-switch; Load-balancing; Self-stabilizing; Switched-mode) Switched-mode
26. Harmonics are porduced when the current is imbalanced among phases. T/F False
27. Explain the difference between how linear and nonlinear loads draw current.
28. Harmonics create problems by causing excess heat in a transformer. T/F True
29. Capacitors alone can be added to a circuit to compensate for distortion power factor. T/F False
30. Standard transformer K-ratings are 1,2,5, and 10 False
31. The primary function of a 3-phase __ is to reduce the fifth and seventh harmonic currents generated by six-pulse (six-diode) converters that change AC to DC. (Next Card)
(Harmonic filter; Harmonics mitigating transformer; K-rated transformer; Phase-shifting transformer Harmonic filter
32.Match the harmonics to the illustration page 95 ( 5th, 7th, 3rd, Fundamental) page 95
Created by: JoshHampton
 

 



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