Industrial Engineer · phase 13 of 16
THD
Total Harmonic Distortion, a ratio that summarizes harmonic content relative to the fundamental component.
The Explain card
- Plain English
- Total harmonic distortion is one number that sums up how much harmonic content a waveform carries compared with its fundamental. It is quoted separately for voltage and for current.
- Example
- A single six pulse drive can draw current with a THD around 80 percent. Adding a line reactor brings it near 35, and an active front end brings it under 5.
- Why it matters
- Standards like IEEE 519 set limits on current distortion at the point where the plant meets the utility, and voltage distortion limits for what the plant sees. THD is the number the harmonic study reports and the number the mitigation is bought against.
- Hook
- How far from a sine, in one percentage.
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.
