A 1,000 kVA transformer feeding six-pulse VFDs, spot welders and single-phase loads is a textbook harmonic source. Field measurements on such busbars typically show current THD of 25–40 % at the PCC, with the 5th and 7th orders dominant. Third-order currents add up in the neutral conductor and overheat it. Fixed capacitor banks rarely survive this environment. When the natural resonan...
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...
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