The general categories of harmonic producing nonlinear loads are some of the following except for ___.

• A. Power electronic equipment
• B. Arcing devices
• C. Iron saturating devices
• D. Incandescent lighting

Answer: (D)

Harmonics come from loads that don’t draw current in a simple, proportional way to the applied voltage. When a load distorts the current waveform, it injects harmonics into the system. Power electronic equipment switches rapidly and draws current in pulses, which creates a broad harmonic spectrum. Arcing devices introduce irregular, rapid changes in current, also producing harmonics. Iron saturating devices have a nonlinear magnetization characteristic; when the core saturates, the current no longer follows voltage linearly, generating harmonics. Incandescent lighting acts mostly as a linear resistive load—the filament resistance stays approximately proportional to temperature and voltage, so the current remains close to a sine wave and does not produce significant harmonics. Therefore incandescent lighting is the exception.