High THDi — total harmonic distortion of current — is the ratio of the RMS value of all current harmonics to the fundamental current, expressed as a percentage. It rises when nonlinear loads such as variable frequency drives (VFDs), rectifiers, UPS units and chargers draw current in pulses instead of a clean sine wave. A high reading must be explained, not simply cleared: measure the s...
Harmonics are extra currents and voltages at integer multiples of the supply frequency that non-linear loads draw on top of the fundamental sine wave. Their effect is costly: transformers, motors and neutral conductors overheat, relays mis-trip, and equipment life shortens even below rated load. This guide covers measurement at the point of common coupling (PCC) and how to compare the main mitigat...
Active Harmonic Filter vs Passive Harmonic Filter A 480 V production bus can appear stable until several VFD-driven lines ramp together. Then the neutral conductor runs hot, transformer temperature rises, capacitor steps fail, and PCC THDi may exceed the site target. An Active Harmonic Filter addresses this condition by measuring distortion and injecting opposing current rather than ...
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