Power Quality Disturbances

Power quality disturbances can be categorized into the following seven basic groups.

  • An outage is a complete loss of power. A temporary outage lasts anywhere from 3 seconds to 1 minute. A long term outage would last longer than 1 minute.

    Possible Causes
    • Accidents, acts of nature, etc. which require the proper operation of utility equipment (like fuses)
    • Internal short circuit resulting in the proper operation of a customer's breakers and fuses
  • A momentary outage is a very short loss of power lasting from 1/120th of a second to 3 seconds. This is often seen as a "blink" in your lights.

    Possible Causes
    • Accidents, acts of nature, etc. which require the proper automatic operation of utility protective equipment
  • An undervoltage or overvoltage is any long-term change (lasting more than a minute) below or above normal voltage.

    Possible Causes
    • Overloaded wiring or equipment
    • Poor voltage control possibly due to large load swings or improper transformer settings
    • Voltage drop due to undersized wiring and faulty or poor electrical connections
  • A sag or swell is any short-term (lasting less than one minute) decrease (sag) or increase (swell) in voltage.

    Possible Causes

    • Major equipment start-up or shutdown
    • Short circuits
    • Improper electrical connections
    • Sudden load reduction
  • A surge or transient is a sudden change in voltage up to several thousand volts lasting a few microseconds (a microsecond is one millionth of a second).

    Possible Causes
    • Lightning
    • Proper operation of utility fuses, reclosers, and breakers
    • Turning on or off large equipment
    • Operation of welding equipment
  • Noise is an unwanted electrical signal of high frequency that alters the normal voltage pattern (sine wave). An example of the result of noise would be the distorted picture you may get on a computer screen when a microwave is turned on.

    Possible Causes
    • Electronic equipment
    • Radar transmitters
    • Radio and television broadcasts
    • Operation of welding equipment
    • Heaters, thermostats, and loose wiring

  • Harmonic distortion is the alteration of the normal voltage pattern (sine wave) due to "non-linear" loads (like electronic equipment). All electronic devices (those having transistors for example) draw electricity differently than non-electronic equipment and distort the normal voltage pattern.

    Possible Causes
    • Operation of non-linear loads such as fluorescent ballasts and computer power supplies
    • Operation of battery chargers

Potential Solutions

To keep your business up and running with reliable power, some of the following equipment may be useful.

  • An alternate power supply usually driven by a gas or diesel engine.
  • Designed to limit instantaneous high voltages. Also known by a number of names, such as surge suppressor, surge arrestor, and surge diverter.

  • Eliminates interference that may interrupt the proper operation of electrical or electronic equipment. This interference is known as electromagnetic interference (EMI). Electronic devices can be a source of this interference.
  • Protects sensitive electronic equipment by buffering electrical noise.
  • Maintains voltage output within a desired limit despite varying input voltage. Regulators provide little or no protection against surges or noise.
  • Designed to maintain a constant voltage output over a wide range of input voltages. As a result, input voltage variations do not pass through the transformer.
  • Designed to improve the quality of power supplied to critical loads and to generate the required voltage and current when power interruptions, voltage variations, or frequency variations occur. A UPS has batteries as an internal source of energy and uses this energy to provide AC power to selected equipment even if the utility power is interrupted.
  • Designed to come between the power from the utility system and critical equipment within the business. The motor takes power from the utility system and then generates power for critical equipment. Acting as a buffer, motor-generator sets provide regulated, conditioned power to connected equipment.

  • Designed to limit the periodic or continuous distortions of the normal voltage wave pattern (sine wave) caused by non-linear loads. Non-linear loads (like all electronic equipment) draw electricity differently than linear loads and distort the normal voltage pattern.
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