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Quick guide to power quality symptoms and causes

Mar 9, 2020 | Power quality
Quick guide to power quality symptoms and causes

To the untrained eye, problems in electrical distribution systems or the equipment connected to the circuit may not be recognizable as power quality problems. When no immediate problem is apparent, it may be written off as just an old breaker that needs replacing or a one-time nuisance reset. You might look at types of loads on the system and monitor for harmonicsunbalance or disturbance patterns.

Harmonic distortion issues and voltage and current anomalies represent the areas where common problems in power quality occur. Voltage and current anomalies can produce problems; however, many can be corrected before they damage equipment. Use this chart to help spot the symptoms:

IssueSymptomsPotential causes
Dips or Sags
  • Lighting dimming, computer lockups, relay and contactor chatter or complete dropout, equipment and system shutdowns
  • Spurious and unexplained alarms and shutdowns
  • Starting large loads, especially large inductive
  • Similar operations in neighboring facilities
  • Severe weather
Swells
  • Failed power supply
  • Overvoltage shutdowns and alarms on variable frequency drives (VFDs)
  • Fault on single phase of three-phase system
  • Sudden load decrease
  • Capacitor bank switching
Transients
  • Flashover and arcing effects in distribution equipment
  • Damaged insulation
  • Failed electronics
  • Computer lockups
  • Lightning strikes
  • Switching of capacitors
  • Reenergizing systems after a power failure
  • Sudden stoppage of large equipment
  • Dirty or worn contactors
InterruptionsEquipment shutdownsMomentary loss of utility power
UnbalanceOverheated three-phase motors and transformers
  • Unbalanced loads across individual phases of three-phase panelboards
  • Unbalanced utility supply
  • Operation of single-phase welders
  • Open-delta transformers
Harmonics
  • Overheated neutral conductors
  • Overheated transformers
  • Overheated inductive motors
  • Spurious and unexplained alarms and shutdowns of electronic equipment
  • Nonlinear loads such as switching power supplies
  • Converter sections of uninterruptible power supply (UPS), VFDs and battery chargers
  • Welders
  • Arc furnaces