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This is a listing of the power quality terms used in this website and their meanings.


battery backup - uninterruptible power supply used for computers and other electronic systems to project the data from loss during a power outage. Note: Most battery back-up units do not protect the hardware or prevent "screen freeze".
blackouts - total loss of commercial electrical power
blink - a short duration voltage sag or outage.
branch circuit - an individually protected electrical circuit originating at the service panel and ending at the electrical outlets
brownouts - a long duration voltage sag (low voltage) sometimes caused by the utility to reduce the load on the electrical system.
building transformer - an electrical device for changing high voltage. usually utility voltage on the incoming side and user voltage on the customer side.
bump - an undefined term used to describe a short duration rise in voltage, may or may not be detrimental to equipment operations.
clean ground - an undefined term used to describe an earth connection that does not contribute to misoperation of electrical equipment. see computer ground, or isolated ground.
clean power - an undefined, imprecise term sometimes used to describe the electrical power requirement so it will not cause problems for electronic equipment operation.
common mode noise - abnormal signals appearing between a current between current carrying line and associated ground. can be between neutral or phase and ground.
crest factor - the ratio of peak to RMS value of the voltage or current waveform. a sinewave has a crest factor of 1.414 to 1. a switchmode power supply current waveform usually has a crest factor of 3 or 4 to 1.
critical load - circuit or feeder that has an important or costly operation associated with it.
dirty power  - an undefined, imprecise term sometimes used to describe the electrical power when it causes problems for electronic equipment operation.
distortion - abnormal waveshape of voltage or current.
drop-out - total loss of voltage for a short period of time
electrical disturbance - a change in the electrical power that causes misoperations of appliances connected to the electrical system. Can be caused by other electrical loads or by events outside the building.
electromagnetic compatibility - a term used to describe the tolerance level of electrical appliances to normal electrical disturbances and the ability of the utility to maintain a constant level of power quality.
enclosure - protection for components used in the electrical system
fault - a term used to describe a problem occurring in the electrical system, usually a short to ground that causes a breaker to operate.
flicker - the electrical power quality parameter that describes the variation light intensity of a fluorescent light caused by very slow variations in voltage. The voltage varies at 1/2 or less of the fundamental frequency.
glitch - an undefined, imprecise power quality term used to describe a voltage variation (usually very short duration) that causes electronic equipment to misoperate.
ground - generally referring to the earth connection of the electrical system
ground loop - unexpected current in a non current carrying conductor. tow or more points of an electrical system connected to the earth at different points.
ground noise - an undefined, imprecise term used to describe unwanted electrical signals appearing between the earth conductor and any other conductor.
harmonic - a signal at a frequency that is a multiple of the fundamental frequency.
harmonic distortion - waveform changes caused by the power supplies of certain electrical or electronic appliances.
harmonic resonance - the power quality term used to describe the condition that sometimes occurs in electrical system. this condition causes high currents to flow through capacitors and damage them or clear fuses in related circuits.
impulse (notch) - a disturbance of the voltage waveform that is less than about one millisecond
interruptions - (see also power outage or momentary) - a complete stop in the flow of electricity, lasting from a fraction of a second to hours.
isolation - electrical isolation between input and output. such as an isolation transformer or optical coupler.
interharmonics - this power quality term refers to the distortion of the waveform that is at the frequency which is not an even multiple of the fundamental frequency. For example, a harmonic would be 2, 3, 4 times the fundamental frequency. an interharmonic would be 1.5 or 3.4 or 7.2 multiple of the fundamental.
momentary - an undefined, imprecise term used to describe a short duration PQ event, such as a voltage sag or surge.
noise - non-damaging distortion of electricity - which interferes primarily with communications appliances-caused by other appliances and electronic lighting.
non-linear load - an electrical load that uses power in pulses or other waveform that does not track the sinewave. almost all electronic power supplies are non-linear loads.
notching - a negative or positive change in the waveshape that repeats cycle to cycle. Most often caused by high peak currents of variable speed drives or other phase loads.
oscillatory transient - a power quality term used to describe a voltage transient that rises sharply to some level and then degrades over time with an waveform that decreases in frequency and amplitude.
over voltage - an increase in the normal voltage level lasting for seconds or minutes.
outage - long term loss of voltage Long term usually means several minutes.
power quality problem - the difference between the quality of electricity at an electrical outlet and the quality of the electricity required to reliably operate an appliance, resulting is misoperation-operation or damage.
power surge - an undefined, imprecise term sometimes used to describe a transient that damages equipment.
radiated noise - sometimes referred to as EMF or RFI noise by engineers, is emitted through the air instead of the electrical system and is received by televisions, hearing aids, computer monitors, and other communication appliances
raw power - an undefined, imprecise term sometimes used to describe power as it comes from the utility without filtering.
under voltage - a decrease in the normal voltage level lasting for seconds or minutes.
sag (also called dip or voltage sag) - a decrease of the normal voltage level lasting less from a few cycles to a few hours.
screen freeze (lock-up) - a term used to describe the situation when a computer or computerized equipment stops its operation and non of the controls function. any automated equipment stopping unexpectedly.
service panel (enclosure) - an electrical cabinet that houses circuit breakers or fuses for building or a portion of a building.
spikes (voltage) - an imprecise, undefined term used to describe the very short duration voltage transient that caused damage to electronic equipment.
swell - an increase in the normal voltage level lasting from a few cycles to a few hours.
surge - a sudden increase of electric current or voltage
surge arresters - electrical devices used to limit sudden changes in voltage or current. They can be either connected in series to limit current or in parallel to limit voltage. They are used to protect other electrical equipment and electrical systems.
surge protectors - see surge arresters
surge suppressers - see surge arrests
transients - short duration, fast rise time voltage changes, that are caused by lightning, large motors starting, utility switching operations, and other appliances switching.
triplens - a term referring to the harmonics that are a multiple of three times the fundamental frequency. For example, 3rd, 9th, 15th and so on.
THD total harmonic distortion - a waveshape change caused by the presence of multiples of the fundamental frequency of the ac power.
TVSS - transient volt surge suppresser, see surge suppressers
under voltage - a steady state situation where the ac line voltage is below nominal value.
UPS - uninterruptible power supply, containing batteries that store energy which can be used during power interruptions (See battery backup)
voltage - electrical pressure, or electromotive force (emf)
voltage dip - see sag
voltage imbalance - a power quality term used to describe the variation in voltage between phases in a three phase system. Calculate by measuring each phase, take the average of the three phases and calculate the percentage difference to phase with the greatest difference.
voltage regulation - a term used to describe the voltage variation. usually described as a percent of nominal.
voltage sags - see sags
voltage variations - changes in voltage value
waveform - a term used to describe the shape of an electrical signal, obtained by plotting a graph with voltage vs time.
wye - a three phase 4 or 5 wire connection with a single common neutral, a single ground and three phase conductors

If you have any questions, comments or would like more detailed descriptions about this listing of terms, please contact us.

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