Power Quality

Types of Power Quality Problems

Power quality disturbances range from surges that last only microseconds to outages that continue for hours. Some common examples include the following:

Temporary Interruption

  • Description: Planned or accidental total loss of power in a localized area of community
  • Duration: From 2 seconds to 2 minutes
  • Causes: Equipment failure, weather, animals, human error (auto accidents, kites, etc.)
  • Effect: Systems shut down
  • Possible Solutions: Uninterruptible power supply, uninterruptible power supply with generator

Long-Term Outage

  • Description: Planned or accidental total loss of power in a localized area of community
  • Duration: Over 2 minutes
  • Causes: Equipment failure, weather, animals, human error (auto accidents, kites, etc.)
  • Effect: Systems shut down
  • Possible Solutions: Uninterruptible power supply, uninterruptible power supply with generator

Momentary Interruption

  • Description: Very short planned or accidental power loss
  • Duration: Milliseconds to second or two
  • Causes: Switching operations attempting to isolate an electrical problem and maintain power to your area
  • Effect: Equipment trips off, programming is lost, or disc drive crashes
  • Possible Solutions: Uninterruptible power supply, motor generator, standby power supply

Sag or Undervoltage

  • Description: A decrease in voltage
  • Duration: Milliseconds to a few seconds, undervoltages are sags that are longer than a few seconds
  • Causes: Major equipment start-up or shutdown, short circuits (fault clearing), undersized electrical circuit
  • Effect: Memory loss or data errors, dim or bright lights, shrinking display screens, equipment shutdown/reset
  • Possible Solutions: Relocate computer to a different electrical circuit, voltage regulator, constant voltage transformer (Ferro-resonant transformer), power conditioner, uninterruptible power supply, motor generator, capacitor/flywheel/superconductor storage

Swell or Overvoltage

  • Description: An increase in voltage
  • Duration: Milliseconds to a few seconds, overvoltages are swells that are longer than a few seconds
  • Causes: Major equipment start-up or shutdown, short circuits (fault clearing), undersized electrical circuit
  • Effect: Memory loss or data errors, dim or bright lights, shrinking display screens, equipment shutdown
  • Possible Solutions: Relocate computer to a different electrical circuit, voltage regulator, power conditioner, uninterruptible power supply, motor generator

Transient, Impulse, or Spike

  • Description: A sudden change in voltage up to several hundred to thousand volts.
  • Duration: Microseconds
  • Causes: Utility switching operations, starting and stopping equipment or machinery, static discharges, lightning
  • Effect: Processing errors, data loss, burned circuit boards
  • Possible Solutions: Surge suppressor (for transients), power conditioner, motor generator

Notch

  • Description: A disturbance of opposite polarity from the waveform
  • Duration: Microseconds
  • Causes: Utility switching operations, starting and stopping equipment or machinery, static discharges, lightning
  • Effect: Processing errors, data loss, burned circuit boards
  • Possible Solutions: Surge suppressor (for transients), power conditioner, motor generator

Noise

  • Description: An unwanted electrical signal of high frequency from other equipment
  • Duration: Sporadic
  • Causes: Electromagnetic interference: from appliances, microwave and radar transmissions; from radio and TV broadcasts, arc welding, heaters; from laser printers, thermostats, loose wiring; or from improper grounding.
  • Effect: Disturbs sensitive electronic equipment, but is usually not destructive. It can cause processing errors and data loss.
  • Possible Solutions: Isolation transformer, power conditioner, uninterruptible power supply, motor generator

Harmonic Distortion

  • Description: An alteration of the pure sine wave (sine wave distortion), due to non-linear loads, on the power supply
  • Duration: Sporadic
  • Causes: Non-linear loads
  • Effect: Causes motors, transformers and wiring to overheat
  • Possible Solutions: Electrically separate non-linear loads and wire per Appendix A to limit harmonic distortion