Characterizing PQ values Power Quality Incidents

Published by Terry Chandler, Director of Engineering, Power Quality Thailand LTD/Power Quality Inc., USA.


  • A PQIncidenstTM occurs when one or more of the PQ parameters exceeds a specification or causes a problem for a load
  • A PQIncidenstTM is comprised of one or more events
  • A PQIncidentsTM is a definable point in time and power quality characteristic
  • Most PQIncidentsTM are associated with significant changes in the voltage at the utility level

Sources of PQIncidentsTM

  • Lightning
  • Equipment failure
  • Wind
  • Phase to ground short circuits
  • Fuses clearing/breakers tripping
  • Loads switching

Power Reliability

  • Is the presence of voltage at the meter point. (measured to approx. 1 to 2 sec)
  • Depends on the utility
  • Depends on the contract for power reliability and Power Quality

Power Quality

  • The values of the various PQ parameters at the meter point. ( less than 1 to 2 sec)
  • The effect on the operation of the factory or a piece of equipment. IE elevator, computer, process controller etc
  • The effect on the electrical system of power polluting loads

What are the various PQ parameters?

  • Voltage sags (dips) low line voltage (brown outs) RMS values
  • Voltage waveform events (subcycle)
  • Voltage transients (fast spikes)
  • Harmonics
  • Voltage imbalance
  • Flicker
  • Interruptions planned or unplanned
  • Other Wiring and Construction (design)

Identify PQIncidentsTM

  • Review the customer input and form.
  • Review RMS graphs of the values of all PQ parameters.
  • Review the PQ event data
  • Identify time of day and date of occurrence

Characterize the PQIncidentsTM

  • Determine the duration and magnitude
  • Determine the source (load caused?)
  • Determine if the source can be prevented
  • Determine if an auxiliary power source is needed to “fill in the energy loss”
  • Document the PQIncidentsTM, the source and solution

Why use PQIncidentsTM?

  • Reduce data to manageable sizes
  • Clear the fog on events
  • Focus on the major issues first.
  • Solve the major problems and the minor ones may not matter

General ITIC curve (1997)

PQ class PQincidents_itic 

11 kVA CBEMA PQIncidentsTM

PQ class PQincidents_itic2


  • PQIncidentsTM summarizes the data
  • Provides a simple model for economic analysis

Please feel free to leave a question in the comments section or contact Terry Chandler,,


Published by PQBlog

Electrical Engineer

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