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PMI PQ Ruler

Category: PQ Theory

Check out the contents of PMI's practical PQ Ruler, detailing various power quality information useful to engineers.




Voltage unbalance is the difference in phase voltage among the three phases, compared to the average, as shown in the formula.


Large unbalance (over several percent) can cause excessive heating in motors, VFD controllers, and other 3 phase electronic power supplies.


The recommended limit from ANSI C84 is 3%.


Voltage unbalance may be local (limited to the secondary of a distribution transformer), mostly caused by unbalanced secondary loading, or present on the primary, caused by unbalanced feeder loading across all three phases...


This White Paper Includes:

  • Sign Convention
  • Ohm's Law and Power Formulas
  • PF, DPF and Harmonics
  • 60Hz and Cycles
  • Eli the Ice Man
  • Voltage Unbalance
  • IEEE Standards
  • Resonance Frequency
  • Feeder Resonance Formula
  • Voltage Notching
  • Voltage Limits
  • IEEE Std. 141 Flicker
  • IEEE 519 Voltage Harmonic Limits
  • IEEE 5129 Current Harmonic Limits
  • IEEE 1453 Flicker
  • Transient Definitions

Download White Paper Here