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info@e-cube.inPower factor correction solves for reactive power, but there’s a second, less visible distortion sitting on top of many industrial supplies: harmonics. A plant can have a near-perfect displacement power factor and still suffer overheating transformers, nuisance tripping, and capacitor bank failures — all traceable to harmonic distortion the electricity meter never shows directly.
What a harmonic actually is
India’s grid supplies a clean 50 Hz sine wave. Non-linear loads — VFDs, UPS systems, rectifiers, LED drivers, arc furnaces, welding sets — don’t draw current in a smooth sine wave; they draw it in pulses. Fourier analysis shows this distorted current waveform as the fundamental 50 Hz component plus a series of harmonics at integer multiples of it: the 3rd (150 Hz), 5th (250 Hz), 7th (350 Hz), and so on. The cumulative effect of these harmonics is expressed as Total Harmonic Distortion (THD), usually quoted separately for current (THDi) and voltage (THDv).
Why it matters even when PF looks fine
Harmonic current does no useful work, but it still flows through cables, transformers and switchgear, adding to I²R losses and heating without contributing to output. IEEE 519 and most utility connection agreements set THD limits specifically because harmonics propagate upstream and can distort the voltage seen by neighboring loads and even the grid itself.
Common symptoms of high harmonic distortion
- Transformers and neutral conductors running hotter than load calculations predict (triplen harmonics add up in the neutral rather than cancelling).
- Capacitor banks failing prematurely or humming audibly — capacitors present low impedance to higher-frequency harmonics and can resonate with system inductance, amplifying distortion instead of absorbing it.
- Nuisance tripping of MCCBs and protection relays with no obvious overload.
- Electronic equipment, PLCs and sensitive controls misbehaving intermittently.
Where it comes from on a typical shop floor
VFDs are the most common single source in modern facilities — a 6-pulse VFD front end can inject significant 5th and 7th harmonic current. UPS systems, LED and CFL lighting, and switch-mode power supplies contribute odd harmonics as well. As facilities modernize toward more VFD-driven motor control (genuinely a good thing for energy efficiency), harmonic load as a share of total demand tends to climb even as overall consumption falls.
Measuring before treating
Harmonic analysis with a power analyzer capable of spectral measurement (not just RMS current/voltage) identifies which harmonic orders dominate and at what magnitude, at the point of common coupling and at individual problem loads. This determines whether a facility needs simple detuned reactors on its capacitor banks, dedicated passive filters tuned to specific orders, or active filtration for a broad, shifting harmonic spectrum.
Related reading: see our harmonic basics primer and get your facility’s spectrum measured with a harmonic analysis service.