Industrial Engineer · phase 13 of 16
Harmonics
Current or voltage components at integer multiples of the fundamental frequency that distort the supply waveform.
The Explain card
- Plain English
- Harmonics are currents and voltages at whole number multiples of the line frequency, riding on top of the fundamental. A drive's diode front end draws current in pulses rather than in a sine, and pulses are full of harmonics.
- Example
- A plant with a dozen large drives sees fifth and seventh harmonic currents on its feeders. The transformer runs warm, the power factor correction capacitors hum, and a sensitive meter reads wrong.
- Why it matters
- Harmonics heat transformers and cables, trip breakers on current they were never sized for, and can violate the utility's limits at the service entrance. Reactors, multipulse rectifiers and active front ends exist to reduce them.
- Hook
- The distortion the drive sends back up the wire.
Where it sits in the deck
Phase 13: VFD Power Quality, Wiring, and Motor Protection
Harmonics, reflected waves, shielded cable and bearing currents: the side effects a drive inflicts on everything around it.
