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