power quality

many tools designed to improve a power supply's quality are not only among the first to suffer from a lack of quality, but are sometimes _ to the problems they are intended to resolve

companies have relied heavily on an increased use of _ to achieve increased productivity

companies invest in additional back-up equipment, which adds to the demand on the power supply and are sensitive to _ in the system

while IT devices can be made more efficient, business's ever - growing reliance on IT still results in a net _ in the use of electrical power

power quality disturbances (PQ phenomena) may result from circumstances that exist _or _ a business's control

_ of all computer problems and _ of all data losses associated with PQ phenomena can be traced back to the power line (utility-supplied power)

from a business perspective, what is considered a significant issue

list the three electrical theory laws used to trace the source of most PQ - related problems

voltages and currents within a facility are generally not pure _.

voltage phasors, or vectors, are seperated by _ degrees in a normal three-phase power distribution system

putting an electronic drive in front of a three phase motor to make an adjustable speed drive or a variable frequency drive alters the phase angles to reflect a

harmonics current are induced by the loads that draw current in a _ waveform.

current vectors will _ significantly when one phase conductor is shorted either to ground or to another conductor

RMS (effective) voltage variations due to PQ phenomena are often referred to as _, _, or _

a _ is a decrease from the nominal voltage supply level

a _ is an increase in voltage level

swells are frequently the result of a sudden _ in load current

interruptions are usually the result of being _ from the fault protection

voltage transients are usually categorized by the shape of the _

_ transients add energy to the voltage waveform, while _ transients subtract energy from the curve

the PQ phenomena classification which encompasses harmonics, inter-harmonics, voltage fluctuations, notching, and DC off sets is waveform _

the main sources of harmonic currents today are at the phase angle controlled _ and _

three-phase, full wave rectifiers cause non-linear harmonic currents since the conduction of current takes place only when the transistor-generated _ allow it, and not throughout the complete 60 Hz cycle

when are even-numbered harmonics found in electrical systems

_, including voice phone systems and local area networks, can be affected by noise

notching can be caused by switching semiconductor creating a brief _ between two phases

a voltage fluctuation ranging from one to 30 Hz is commonly referred to as light _

a _ is one who is familiar with the construction and operation of the equipment and the hazards involved

the use of proper personal protective equipment is intended to _ or _ injury

what single activity was identified as being performed when an accident occurred

connecting or disconnecting the voltage and current probes for power quality monitors can be dangerous depending on the _, _, and _

"the NFPA 70E-2009 standard is so important because it offers examples of _ to comply and not just that you have to comply," says Palmer Hickman, director of Code and Safety Training and Curriculum Development at the National Joint Apprenticeship and Training Committee (NJATC) for the electrical industry

According to NFPA 70B, "Equipment should be de-energized for inspections, tests, repairs, and other servicing.such maintenance tasks can be performed when the equipment is energized provided _ are made to allow maintenance to be performed _."

According to NFPA, "switchboards panel boards, industrial control panels, and motor control centers that are likely to require examination, adjustment, servicing, or maintenance while energized, should be _ to warn qualified persons of potential electric arc flash hazards."

According to NFPA 70B," as a general rule, no electrical apparatus should be worked on while it is _."

what is sometimes the best preparation a person can make to ensure a successful power quality activity

finding a potential problem _ it shuts the system down is perhaps the best PQ scenario

it is usually wise to have the most _ tool doing the monitoring until the source of the problem can be narrowed down.

All PQ audits or troubleshooting task require top of-the-line PQ monitors

the digital multimeter (DMM) is useful for detecting _ unbalances (or imbalances)

a 3% voltage imbalance between phases may result in the need to _ electric motors by 10%

both voltage unbalance and harmonics are generally considered as _ power quality problems

short duration disturbances, such as sags, swells, and transients, are often not _ by DMM-type meters

portable monitors use the _ approach to troubleshoot problems

the ability to set a monitoring device to _ automatically when a power quality event _ allows one to analyze the cause of the problem

portable PQ monitors can provide _ of waveforms and _ for hundreds of parameters

permanently-installed power quality monitoring systems are typically _ and provide the advantage of showing _

most power quality analyzers have accompanying application _ that runs on a PC, which provides event data viewing capability

an electrical worker should have a full understanding of the _ and the _ of the monitoring instrument and the equipment being monitored before implementing or utilizing power quality equipment

a power quality instrument should be _ for the anticipated range of voltage and current levels

follow all installation and operating instructions and only use accessories _ for the instrument

the installation, operation, and maintenance of the instrument must be performed by _ personnel

improper connection of communication equipment to the instrument only affects the the communication equipment

when accurate measurements are needed on sinusoidal waveforms to detect _, only true rms meters should be used

using the wrong _ for the application is one of the most common problems encountered with CTs

connections to voltage and current sources need to be made _ and _

connections between the instrument and the circuit need to be made in accordance with the type of circuit being monitored and with the correct _

if channel A of the instrument is connected to Phase _ voltage but to phase _ current, incorrect power measurements will result

real power, measured in _, is used to determine power quality

volt-amperes-reactive (vars), should only be computed on the _; not the _ in a distorted or unbalanced system

if the instrument has the capabilities, measuring the _ voltage and neutral conductor _ in wyes and single/split phase, circuits will usually provide additional clues as to sources of disturbances

the example above is an example of the _ and _ leads connected to ground four-wire _ circuits

sub-quarter-cycle changes in the wave shape which usually do not trigger on rms variations

high, low, and very low rms variation limits are set to record _, _, and _, respectively, as shown in the figure above

users can usually define the _ of rms summary and wave cycles to be saved before the start, after the start of the trigger, and after the end of the event

parameters such as _ do not need to be checked every cycle, but they are useful to trigger an alarm when the approach limits are reached

data collection and analysis will vary depending upon whether one is conducting an _ or a _ exercise

monitoring to establish a benchmark should be conducted for at least _ to get a more complete picture of the electrical supply

for benchmark purposes, typical _ and _ limits for sag and swell thresholds should be reset to _ and _

the difference between service voltage and utilization voltage allows for _ in facility wiring between the point of utility delivery and the utilization equipment

voltage _ can have a damaging effect on motors and other electromagnetic equipment

in general, transients with peak values _
(how much) the nominal voltage sine wave peak come within the problem - causing range.

DC offsets more than a percent or two of the _ voltage can adverse effects on transformers

the periodic cycling of energy demand is referred to as _

the worst (highest) monthly peak demand value over a year

the ratio of watts to volt-amperes (W/VA) is known as _ power factor

A facility's electric costs can be greatly impacted by replacing older drives with more energy-efficient and better PF drives, along with K-rated transformers that can handle the _ without having to be significantly _

you should be able to identify what problems the facility's equipment is experiencing after starting the monitoring program

for a _ load, the current will decrease proportionally to the voltage drop. for a _ load, current will not decrease or increase proportionally to the voltage sag or swell

when measuring equipment efficiency, monitoring should be conducted over the _ of loading, because the efficiency varies as a function of _

improving a facility's overall efficiency requires a working knowledge of the _ and _ of the major loads

the _ in two improperly -made ground connections causes current to flow in a ground loop path, with possible noise and/or component failures

lowering the _ between the source and the supply can lessen flicker effects

since fluorescent bulbs do not draw current _, lighting can be another source of PQ phenomena

an unbalanced transformer will cause _, as will over-voltage _ of a transformer

what can the high crest factor and heating of harmonics current affects

_ will cause the impedance to change, which will cause a device to draw different amounts of current

_ can cause physical damage to a computer's semiconductors and capacitors

telecommunications circuits are susceptible to harmonic currents being _ into the telecom wiring

the _ values of harmonic distortion could cause the motor to rotate in the same direction as the fundamental frequency, whereas the _ components would try to turn the motor in the opposite direction; both resulting in heat in the motor

harmonic currents can be attributed to current flowing through the shafts in motors with _ shafts

process control equipment (PLCs and computers) possess the susceptibilities of ASDs and IT equipment as well as vulnerability to the _ of the transducers that feed information into analog-to-digital (A/D) converters

imaging equipment tends to draw high current levels that may not be compatible with the electrical infrastructure of the facility or specifically, its _.

Lighting is a _

improperly grounded communication cables between peripherals and the mainframe computer may become a problem when exposed to stong level RF signals through

Although _ faults do not have enough current flow for the fuse or the distribution breaker to operate, they can result in the lights blinking

_ typically has significant harmonic current of the odd harmonics from 3rd to 15th

well-grounded, properly-sized UL listed _ should be installed on any metallic interface that extends outside a structure, including the incoming electric service, phone lines, and any exterior branch circuit

even harmonics are found in most equipment if there are half-wave rectifiers in their circuits.

the majority of the harmonic spectrum on most electrical circuits consists of even harmonics

on a single-phase circuit, the origin of the voltage sag is usually _ if the neutral-to-ground voltage increased significantly during the sag

sag is the sum of the _ in both the line (hot) and the neutral (grounded) wires

when the current in a single-phase circuit cannot be measured, measure the neutral-to-ground voltage to determine if the current _ when the sag at the load occurs

the origin of a voltage sag is the start up of a _ if the voltage quickly drops and then steadily increases

a load or circuit with significant loads with rectified inputs will most likely have a true power factor _ than the displacement power factor

another common source of incorrect data comes from not using current probes within their _

in using TVSSs, voltage transients may not be _ by power quality monitor, but they still there

negative transients _ energy from the voltage sine wave

learning which mitigation solutions will work for which power quality phenomena can be studied from the _ side or the _ side

once a migration device has been installed, it is important to _ that it is providing the expected results

_ cause insulation failure in windings of motors and semiconductor failures in devices such as SCRs or diodes

in general, motors will overheat and power supply outputs will drop out of regulation if voltage drops to less than _ of nominal for more than a _

depending on the capability of the equipment an _ and/or _ is needed to keep the process running without interruption

transient events are either _ or _

transient voltage surge suppressors (TVSSs) are a type type of _ device

the response time of a protector indicates how quickly a suppressor will react to a

capacitor failures and blown fuses are often attributable to a condition where the frequency of the matches the circuit's _ frequency

a line reactor is an inductor used to increase harmonic currents and transients

harmonic filters are normally used to reduce the harmonic effects from _ loads

isolation transformers are used to isolate or de-couple _
from _

installation of an _ is the most common solution for a voltage sag

when the UPS is generating output power, it is responsible for both _ and _ regulation

large scale devices are designed to keep entire facilities operational through _ sags and interruptions

grounding, bonding, and electrical interconnection of an inverter is critical to the proper _ and _ of a renewable energy power source