Electric Power Distribution Handbook, T. A. Short

12. Other Power Quality Issues

Questions

  1. If you have customer equipment damage, and damage appears to be in surge protectors, what’s a likely cause?

    1. Temporary overvoltages
    2. Inrush into electronics
    3. Reclose transients

  2. If you have customer equipment damage, and damage appears to be in fuses, what’s a likely cause?

    1. Temporary overvoltages
    2. Inrush into electronics
    3. Reclose transients

  3. Capacitor banks:

    1. Cause voltage flicker
    2. Help reduce voltage flicker caused by other loads
    3. Neither

  4. A voltage flicker between 123 and 120 V once per second may cause complaints.

    1. True
    2. False

  5. If you have customer equipment damage, and damage appears to be in fuses, what’s a likely cause?

    1. Temporary overvoltages
    2. Inrush into electronics
    3. Reclose transients

  6. Which of the following is most sensitive to temporary overvoltages?

    1. Incandescent bulbs
    2. Computers
    3. Clock radios
    4. Surge suppressors

  7. Which of the following is least sensitive to temporary overvoltages?

    1. Incandescent bulbs
    2. Computers
    3. Clock radios
    4. Surge suppressors

  8. Will a series capacitor help reduce voltage flicker from a large photovoltaic installation?

    1. Yes
    2. No
    3. It depends on the line impedances

  9. Will a static var compensator help reduce voltage flicker from a large photovoltaic installation?

    1. Yes
    2. No
    3. It depends on the line impedances

  10. Switching surges tend to be worse on higher-voltage distribution systems.

    1. True
    2. False

Problems

  1. On a 12.5-kV system, for a 1200-kvar capacitor bank 5 miles from the substation, find the natural switching frequency of the bank in hertz. Assume that the line has a positive-sequence reactance of 0.6 ohms/mi, and the substation has a reactance of 1.0 ohms.

  2. For a 900-kvar bank on a 12.5-kV system, how far from the substation would the capacitor be to resonate at the seventh harmonic? Assume the line has a positive-sequence reactance of 0.6 ohms per mile and a zero-sequence reactance of 2.1 ohms/mile.

  3. For the same assumptions in the previous problem, find the location for the capacitor bank to resonate at the ninth harmonic.

  4. For a voltage that bounces between 120 and 118 V, find the threshold in the time between dips for the flicker to go above the GE flicker curve.

  5. For each of the following sets of line-to-ground voltages, find the percent voltage unbalance and the percent negative-sequence voltage:

    1. 120∠0°, 118∠-120°, 117∠120°
    2. 120∠5°, 120∠-125°, 120∠125°
    3. 120∠5°, 118∠-125°, 117∠125°

Projects

  1. Using R, Matlab, Excel, or some other tool, write a routine to generate a graph of the resonant frequency of a circuit as a function of distance from the substation based on the system voltage, the size of the capacitor bank, and the substation and line impedances.

  2. Using ATP, EMTP-RV, OpenModelica, or another transient tool, model the switching of a capacitor bank for the following scenario:

    • Three-phase mainline with 336-kcmil AAC in a horizontal crossarm configuration on an 8-ft arm
    • Neutral = 3/0 AAC, 4-ft below the crossarm.
    • Pole height = 40 ft
    • 1200-kvar switched bank, 3 miles from the substation
    • Energize each phase separately

    Find the peak magnitude and predominant frequency for the worst switching case.

    Next, repeat the simulation, but put another fixed 1200-kvar bank 300 ft from the switched bank on the source side.



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To the extent possible under law, Tom Short has waived all copyright and related or neighboring rights to these study questions. This work is published from the United States. Please use this material however you want.