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Although specialists use complex equations for precise descriptions and analysis, the following definitions are adequate for most discussions with your local utility account managers, distribution engineers, and power quality consultants and vendors.
Harmonic distortion
Continuous or sporadic distortions of the 60-hertz (Hz) voltage sine waveform, usually caused by microprocessor based loads in the building such as computer power supplies, lighting ballasts, and electronic adjustable speed drives. Harmonics can also be transmitted from an energy user down the block. These can cause telecommunications or computer interference; overheating in motors, transformers, or neutral conductors; decreased motor performance; deterioration of power-factor correction capacitors; or erratic operation of breakers, fuses, and relays.
Interruption, momentary
A very short loss of utility power that lasts up to 2 seconds, usually caused by the utility switching operations to isolate a nearby electrical problem.
Interruption, temporary
A loss of utility power lasting from 2 seconds to 2 minutes, caused by a nearby short circuit due to something like animals, wet insulators, or accidents. Corrected by automated utility switching.
Long-term outage
A loss of utility power lasting more than 2 minutes due to major local, area, or regional electrical events.
Noise
Sporadic voltage changes consisting of frequencies higher than the normal 60-Hz power frequency due to any number of causes, including arc welders, loose wiring, and nearby radio and TV transmitters.
Sag
A short-term decrease in voltage lasting anywhere from milliseconds up to a few seconds. Sags starve a machine of the electricity it needs to function, causing computer crashes or equipment lock-ups. Usually caused by equipment start-up-such as elevators, heating and air-conditioning equipment, compressors, and copy machines-or nearby short circuits on the utility system.
Spike
A very brief (nanoseconds to milliseconds) change in voltage ranging from tens to thousands of volts. Can be produced by utility and customer equipment operations, nearby lightning strikes, falling tree limbs on power lines, and even static discharges.
Surge
A short-term increase in voltage, lasting up to a few seconds. They are due either to customer equipment operation, such as air conditioners or motors switching on and off, or to utility activities, such as capacitor switching.
Transient
A sudden momentary change in voltage. Also called a spike.
Undervoltage
A decrease in voltage lasting longer than a few seconds. Usually due to undersized wiring at the facility but can also be caused by overloaded utility circuits and result in brownouts.
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