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Power Quality Terms


Electrical Noise

People most commonly associate electrical noise with interference that can be seen on your TV or heard as static on your AM/FM or HAM radio. For example, a person watching TV while someone in the kitchen started using a blender or mixer, the TV screen becomes "snowy" and the sound became “static.”

Unfortunately, many of the things that can cause electrical noise are hard to detect. Almost anything that uses electricity can cause electrical noise that produces audio or video interference. (For example, a fluorescent light could have a faulty ballast, a motor may have a loose connection, a furnace may have a faulty control, etc.). The sources for interference can come from inside your home, your neighbor's home, or somewhere on the electric utility’s system.

Another type of electrical noise is one which disrupts data lines and affects performance of electronic equipment. It is characterized by the presence of unwanted low level electrical signals on the power line. Electrical noise of this type is sometimes a result of bad grounding, or simply picked up from nearby equipment (walkie-talkies, cell phones, arcing devices, etc.). It is especially likely to occur if there is an inadequate or improper equipment ground or when an equipment cable is unshielded or improperly terminated. Although not as harmful as transients, noise can cause performance problems and data disruptions in electronic equipment.


Flickering happens when voltage variation is large enough and long enough that it can be seen as a change in electric light source intensity. It usually results from adding and removing large power loads, like spot welding and starting motors. If the voltage variation is severe, it may cause problems with sensitive loads.


Harmonics are primarily the result of the today's modern electronic equipment. Today's electronics are designed to draw current in "pulses" rather than in a smooth, sinusoidal manner as older, non-electronic equipment did. These pulses cause distorted current wave shapes, which cause distortion of the voltage. Current and voltage harmonics can cause such problems as excessive heating of wiring, connections, motors, and transformers and can cause inadvertent tripping of circuit breakers.


Outages are longer term events (several seconds to hours) caused by external factors. These include: fallen trees, car accidents, animals in contact with lines, operation of utility protective equipment, and weather conditions.

Voltage Sags

Sags are momentary (typically a few milliseconds to a few seconds duration) under-voltage conditions and can be caused by a large load starting up (such as an air conditioning compressor or large motor load) or operation of utility protection equipment. Sags often appear as flickering lights and can cause equipment shutdown. A sag of just a few milliseconds can mean a complete blackout for some sensitive equipment.

Voltage Swells

Swells are momentary (typically a few milliseconds to a few seconds duration) over-voltage conditions which can be caused by such things as a sudden decrease in electrical load or a short circuit occurring on electrical conductors. Voltage swells can affect the performance of sensitive electronic equipment, cause data errors, produce equipment shutdowns, and can cause equipment damage.

Voltage Transients

A transient (sometimes called impulse) is an extremely fast disturbance (millionths of a second to a few milliseconds) evidenced by a sharp change in voltage. Transients can occur on your electric, phone, or even cable TV lines. They can be caused by such things as lightning, trees falling on power lines, ice and snow, and cycling equipment ON and OFF. Transients can originate from inside or outside your home. Equipment, such as air conditioning, pump motors, photocopiers, and even electric hand tools can all cause transients when cycled on and off. These impulses are similar to lightning strikes but are much smaller. However , they can cause electronic equipment to break down over time.

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Maine Public Service District Bangor Hydro District


Versant Power provides electric delivery service to two areas – the Bangor Hydro District and the Maine Public District.

            The Bangor Hydro District includes Hancock, Piscataquis and Washington Counties and most of Penobscot County.
            The Maine Public District serves Aroostook County and a small piece of Penobscot County.

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