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82 question Harmonics correspondence course based on the 2005 NEC.   Course #8258

 

  1. _____ is the sum of the product of each harmonic current squared and that harmonic number squared for harmonics from the fundamental (60 Hz) to the highest harmonic of any measurable consequence.
  1. X Factor
  2. Y Factor
  3. K Factor
  4. V Factor

 

  1. A nonlinear load is one that opposes the applied voltage with constant impedance, resulting in a current waveform that changes in direct proportion to the sinusoidal change in the applied voltage.

     A. True
     B. False

  1. _____ is an example of a linear load.
  1. Resistance heating
  2. Incandescent lighting
  3. Electronic ballasts
  4. both a and b
  1. In common electrical distribution systems in the United States, the fundamental frequency is _____.
  1. 60 Hz
  2. 30 Hz
  3. 20 Hz
  4. 10 Hz
  1. A linear load is one that does not oppose the applied voltage with constant impedance.

      A. True
      B. False

  1. Typical office equipment nonlinear loads have the load on during most of the voltage waveform.

      A. True
      B. False

  1. The square root of the sum of the square of all harmonic currents present in the load excluding the 60 Hz fundamental is called the _____.
  1. triplen harmonic
  2. voltage harmonic distortion
  3. total harmonic distortion
  4. variable harmonic distortion

Types of Nonlinear Loads

  1. Which of the following is a contributor of reflective harmonic currents?
  1. personal computers
  2. welders
  3. rectifiers
  4. all of these

Electronic Equipment Requires Clean Power

  1. Voltage distortion is not a fire safety hazard.

      A. True
      B. False

Past, Present, and Future Trends

  1. The Electric Power Research Institute (EPRI) estimates that currently _____ percent of the total power load is nonlinear.
  1. 5 to 10
  2. 15 to 20
  3. 25 to 30
  4. 30 to 40

Analysis of the Problem

  1. Most building power systems can withstand nonlinear loads of up to _____ of the total electrical system capacity without concern, but when the nonlinear loads exceed _____, some negative consequences begin to appear.
  1. 5 percent
  2. 10 percent
  3. 15 percent
  4. 20 percent

Analysis of the Problem

  1. Most problems caused by harmonics are _____.
  1. equipment failures due to overheating
  2. equipment malfunctions due to voltage distortions
  3. damage to branch circuit and feeder conductors
  4. all of these

 

Capacitor Failures

  1. Inductive reactance (XL) of a circuit increases with increased harmonic frequency, and capacitive reactance increases with increased frequency.

       A. True
       B. False

Electrical Noise

  1. _____ are prohibited from being installed in the same raceway, cable, cable tray, outlet box, or similar enclosure with power or lighting conductors.
  1. Remote-signaling circuits
  2. Power-limited fire alarms
  3. Optical fiber cables
  4. all of these

Electrical Noise

  1. Shielding of cables does not significantly reduce the noise caused by harmonic currents.

       A. True
       B. False

Electromagnetic Equipment Failure

  1. Inductive equipment (such as motors, generators, transformers, relays, coils, etc.) can fail because of inductive heating caused by high-frequency _____.
  1. eddy currents
  2. electromagnetic load
  3. harmonic currents
  4. resistance

Inductive Heating

  1. Hysteresis heating affects ferrous metals that have magnetic properties such as _____.
  1. copper
  2. aluminum
  3. silver
  4. iron

Inductive Heating

  1. Copper and aluminum conductors can increase in temperature because of circulating eddy currents, but they are not affected by hysteresis.

       A. True
       B. False

Grounded (Neutral) Conductor and Terminal Failure

  1. As a conductor or terminal heats up, the resistance will increase _____ for each two and a half percent increase in temperature.
  1. one percent
  2. two percent
  3. three percent
  4. four percent

Grounded (Neutral) Conductor and Terminal Failure

  1. Which of the following multiples of the third order harmonics does not represent a triplen harmonic current?
  1. 3rd
  2. 9th
  3. 12th
  4. 15th

Phase Conductor Insulation Failure

  1. Insulation failure on phase (ungrounded) conductors due to harmonic currents is relatively rare, but insulation does sometimes fail because of overheating due to _____.
  1. eddy currents
  2. skin effect
  3. conductor bunching
  4. all of these

Voltage and Current Distortion

  1. Resistive linear loads supplied by distorted voltage waveforms will operate without any problems.

       A. True
       B. False

Voltage and Current Distortion

  1. K-rated transformers designed to supply nonlinear loads have lower inductive reactance than conventional transformers.

       A. True
       B. False

Voltage Drop

  1. The NEC recommends that the combined full-load voltage drop for branch circuits and feeders not exceed _____.
  1. 2 percent
  2. 5 percent
  3. 10 percent
  4. 12 percent

Voltage Drop

  1. A typical circuit has the voltage distributed among _____.
  1. the power supply
  2. the feeder and branch-circuit conductors
  3. the overcurrent devices
  4. all of these

Voltage Drop

  1. The _____ of a load can be determined by subtracting the voltage drop of the conductors from the output voltage of the power supply.
  1. actual voltage
  2. equipment voltage
  3. operating voltage
  4. neutral-to-ground voltage

Voltage Drop

  1. The voltage drop of the phase and grounded/neutral conductors can be determined by subtracting the operating voltage from the _____.
  1. supply voltage
  2. equipment voltage
  3. operating voltage
  4. neutral-to-ground voltage

Voltage Drop

  1. In a balanced 4-wire multiwire circuit on a wye-connected system that supplies linear loads, the grounded/ neutral conductor does not carry any current.

      A. True
      B. False

Voltage Drop

  1. In addition to grounded/neutral conductor currents from unbalanced circuits, additive triplen harmonic currents cause the grounded/neutral conductor to be overloaded resulting in greater _____ drop.
  1. supply voltage
  2. equipment voltage
  3. operating voltage
  4. neutral-to-ground voltage

Voltage-Drop Examples

  1. According to the National Electrical Code, Chapter 9, Table 9, the resistance of conductors for alternating current with a conductor size of 12 AWG is as follows:
  1. 1.20 ohms per 1,000 feet
  2. 2.0 ohms per 1,000 feet
  3. 0.78 ohm per 1,000 feet
  4. 0.49 ohm per 1,000

Voltage-Drop Examples

  1. According to the National Electrical Code, Chapter 9, Table 9, the resistance of conductors for alternating current with a conductor size of 6 AWG is as follows:
  1. 1.20 ohms per 1,000 feet
  2. 2.0 ohms per 1,000 feet
  3. 0.78 ohm per 1,000 feet
  4. 0.49 ohm per 1,000 feet

 

Busways

  1. Busway grounded/neutral conductors are sized at _____ of the phase ampacity rating, and are vulnerable to failure when used to supply 120V nonlinear loads that produce additive triplen harmonic neutral currents.
  1. 25 percent
  2. 45 percent
  3. 50 percent
  4. 100 percent

Capacitors

  1. When a capacitor becomes tuned to a specific frequency it can result in series resonance (low impedance). This can cause very high currents to flow on the conductors, which can result in _____.
  1. overcurrent protection devices opening
  2. the capacitor overheating
  3. the capacitor failing
  4. all of these

Capacitors

  1. If linear loads are present in a distribution system with power factor correction capacitors, the amount of true RMS current flowing through the capacitors should be measured when all the loads are on.

     A. True
     B. False

Circuit Breakers

  1. The NEC requires that circuits not be loaded more than _____ for continuous loads (3 hours or more).
  1. 50 percent
  2. 60 percent
  3. 70 percent
  4. 80 percent

Conductor Heating

  1. The National Electrical Code conductor ampacities listed in Table 310.16 are based on not more than three current-carrying conductors, bunched in an ambient temperature of_____, at the fundamental frequency of 60 Hz.
  1. 90ºF
  2. 86ºF
  3. 72ºF
  4. 68ºF

Conductor Heating

  1. Since skin effect produces additional heating and the apparent reduction in conductor cross-sectional area (which increases resistance), the current-carrying capacity (ampacity) of the conductor must be reduced.

       A. True
       B. False

Electronic Equipment

  1. When supplied by a distorted voltage waveform, characterized by_____, sensitive electronic equipment can fail to operate properly.
  1. flat-topping
  2. transients
  3. erratic ac voltage zero crossings
  4. all of these

Fluorescent Ballasts

  1. Energy savings of _____ percent can be achieved by using electronic ballasts instead of standard electromagnetic ballasts.
  1. 5 to 10
  2. 15 to 20
  3. 25 to 30
  4. 25 to 50

Fluorescent Ballasts

  1. _____ are a significant contributor of harmonics in building electrical distribution systems.
  1. Fluorescent ballasts
  2. Electronic ballasts
  3. Energy-saving ballasts
  4. Electromagnetic ballasts

Fuses

  1. Fuses are calibrated based on 60 Hz current. Currents at higher frequencies can “blow” the fuse at currents below the fuse calibration rating because of unanticipated inductive heating from _____.
  1. eddy currents
  2. skin effect
  3. hysteresis
  4. all of these

Generators

  1. Generators can be constructed to better withstand the heating effects of harmonic currents by _____.
  1. installing higher temperature-rated conductors
  2. the use of higher quality steel
  3. reducing the thickness of lamination
  4. all of these

Generators

  1. What most generator manufacturers recommend is simply to _____ the generator size or limit the load to some fraction of the generator’s rating (derating the generator).
  1. increase
  2. decrease
  3. double
  4. triple

Generator Derating

  1. There is no recognized method of derating the load on a generator due to nonlinear loads.

       A. True
       B. False

Generator Derating

  1. Nonlinear loads will have a crest factor of 1.414.

       A. True
       B. False

Generator Sizing

  1. If one is attempting to size a generator to a nonlinear load, then the generator kVA size must not be _____ than the kVA load divided by the derating factor.
  1. more
  2. less
  3. equal to
  4. higher

Grounding and Bonding

  1. In general, harmonic currents do not pose problems for grounding systems.

      A. True
      B. False

Motors

  1. Alternating-current motors can overheat because of _____.
  1. reduced voltage
  2. unbalanced voltage
  3. inductive heating
  4. all of these

Motors

  1. If an induction motor is overheating, or unexplained burnouts are being experienced, the first thing to do is verify that the motor is operating within its nameplate current rating.

      A. True
      B. False

Grounded (Neutral) Conductor Failure

  1. Section 220.61(B) of the NEC permits the grounded/neutral conductor for 4-wire, three-phase wye systems to be reduced by including only _____ for that portion of the unbalanced 60 Hz linear load over 200A.
  1. 40 percent
  2. 50 percent
  3. 60 percent
  4. 70 percent

Grounded (Neutral) Conductor Failure

  1. Grounded/neutral conductor reduction is not permitted for 3-wire circuits from a 4-wire wye system.

       A. True
       B. False

Grounded (Neutral) Conductor Failure

  1. The problem of grounded/neutral conductor overload can be solved by _____.
  1. installing a larger grounded (neutral) conductor
  2. reducing the loads
  3. running a separate grounded (neutral) conductor for each phase
  4. all of these

Grounded (Neutral) Conductor Failure

  1. A separate grounded/neutral conductor for each phase conductor may be practical for_____.
  1. feeders
  2. branch circuits
  3. parallel circuits
  4. single-phase circuit

Grounded (Neutral) Conductor Voltage Drop

  1. The neutral current on a balanced 4-wire circuit for linear loads equals _____.
  1. 0A
  2. 24A
  3. 330A
  4. 500A

Overcurrent Protection Devices

  1. The most significant problems associated with harmonic currents within panelboards are grounded/neutral conductor terminal connection failures because of excessive neutral current resulting from _____.
  1. unbalanced phase currents
  2. additive triplen harmonic currents
  3. nonlinear load overloads
  4. both a and b

Panelboard Grounded (Neutral) Terminal Bars

  1. Until 1992, all grounded/neutral terminal bars for panelboards were sized at _____ of the phase current rating.
  1. 50 percent
  2. 75 percent
  3. 100 percent
  4. 200 percent

Raceways

  1. Induction heating occurs when the magnetic fields of the additive triplen neutral currents expand and collapse at a frequency of _____ within the raceway, resulting in eddy currents and hysteresis heating.
  1. 20 Hz
  2. 60 Hz
  3. 100 Hz
  4. 180 Hz

Transfer Switches

  1. Because of nonlinear loads, the grounded/neutral conductor should be sized at _____ of the ampere rating of the phase conductor.
  1. 50 percent
  2. 75 percent
  3. 100 percent
  4. 200 percent

Transformers

  1. Standard transformers are designed to operate within their rated operating temperature rise when loaded not more than their rated kVA, and if the nonlinear load they supply is no more than _____ of the total load.
  1. 5%
  2. 10%
  3. 15%
  4. 20%

Transformers

  1. The primary reason of transformer failure is:
  1. Inductive heating from circulating primary harmonic currents.
  2. Increased resistive heating because of increased eddy currents and skin effect in conductors.
  3. Increased inductive core heating from eddy currents and hysteresis.
  4. all of these

Transformers

  1. At the fifth harmonic, inductive heating is _____ times its percentage of the fundamental current heating.
  1. 9
  2. 15
  3. 25
  4. 35

Transformer Derating

  1. Derating of transformers is useful, but is no guarantee against overheating.

               True
               False

Transformer K-Factor Rating

  1. It is possible to determine the K-factor loading for new tenant space.

       A. True
       B. False

Transformer K-Factor Rating

  1. The information used to determine the K-factor rating can only be derived by the use of a harmonic analyzer.

      A. True
      B. False

Total Harmonic Distortion (THD)

  1. The percent of total harmonic distortion on a transformer, feeder, or branch circuit of equipment has almost no useful purpose for everyday application.

       A. True
       B. False

Transformer Characteristics

  1. Transformers are rated for a specific _____.
  1. reactance
  2. impedance
  3. crest factor
  4. all of these

Relays

  1. It is impossible to generalize the behavior of any particular relay in response to harmonic currents without testing.

       A. True
       B. False

UPS Systems

  1. UPS systems without LC filters can have a total harmonic distortion (THD) of as much as _____.
  1. 35 percent
  2. 45 percent
  3. 55 percent
  4. 65 percent

Utility

  1. When equipment in a facility fails to operate properly, the _____ is the first to be accused of causing the problem.
  1. relay
  2. UPS system
  3. utility
  4. undercarpet wiring

Utility

  1. There is no specific percent of distortion that utilities require customers to meet.

      A. True
      B. False

Variable Frequency Drives

  1. Six thyristors use ac power to turn six solid-state switches on and off, resulting in a current waveform that is similar to a _____ rather than a pure sine wave.
  1. sine wave
  2. square wave
  3. nonsymmetrical waveform
  4. sinusoidal waveform

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----------------------------Educational Course Attendance Verification Form ------------------------

 

Attendee’s Name                                                                                 Date                                        

 

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Credential Number                                                       Phone#                                                            

 

Course Title and Name            Harmonic 82 quiz                                                                                 

 

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                                                                                    Credited Hours            8 hrs                            

 

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