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Formulas for Power and Harmonic Measurements

Category: Harmonics/Interharmonics, Power Quality

PMI recorders use a variety of algorithms to compute various power quality measurements. These formulas for power and harmonic measurements are described in this whitepaper.


A PMI recorder samples up to four pairs of voltages and currents. From these samples it computes RMS voltage and current; real, reactive, and apparent power; power factor and displacement power factor, phase angle, voltage and current THD, and harmonic magnitudes and phases.


The Vip, 600P, Eagle, Eagle 120, and Guardian sample the raw waveforms at rate of 256 samples per powerline cycle (usually 60Hz). The iVS-2S samples at 128 samples per cycle.


The Revolution and Vision sample voltage at a 1MHz rate (one million samples per second), and current at 250,000 samples per second. These high-speed data streams are downsampled to 256 samples per cycle for RMS and power calculations.


The formulas given here are not necessarily those performed by the recorder, but are numerically equivalent expressions...


This white paper includes:

  • Notation & Sampled Data
  • Independent Channels/Single Phase
  • Three Phase WYE
  • Three Wire Data
  • Four Wire Delta
  • 2.5 Element WYE

Download White Paper Here