Power Quality

What is Power Quality?

When power enters your home, it has a few expected characteristics that determine the quality of that power.

  • That it is stable and non-interrupted
  • That it maintains a stable voltage (i.e. 120 V)
  • That it maintains a stable frequency (i.e. 60 Hz)
  • That the waveform that makes up the power signal be transient free
  • That the power signal has low harmonic distortion

Deviations from the above are considered power quality (PQ) issues.

Why Care About Power Quality?

Types of Power Quality Issues

Voltage Sag

When the voltage drops below 10% to 90% of the nominal voltage for a duration of half a cycle to a minute.

Undervoltage

When the voltage drops below 90% of the nominal voltage for a duration of over a minute

Voltage Swell

When the voltage rises to 110% to 180% of nominal voltage for a duration of half a cycle to a minute.

Overvoltage

When the voltage rises above 110% or more of nominal voltage for a duration of half a cycle to a minute.

Voltage Flicker

When the voltage continuously transitions between multiple values between 90% and 110% of nominal voltage

Voltage Transients

When there is a spike, impulse, or surge

Frequency Sag

When the frequency drops below 99.9% of the standard

Frequency Swell

When the frequency rises above 100.1% of the standard

Frequency Fluctuation

When the frequency fluctuates around the standard value

Total Harmonic Distortion (THD)

When the fraction of power in the sub-harmonics in respect to the main harmonic grow beyond a certain threshold

How Distributed Renewables Affect Power Quality

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