Harmonic distortions: what are they, their causes, and typical mitigation strategies?

Harmonic distortions: what are they, their causes, and typical mitigation strategies?

• A. Harmonics are random noise in power lines caused by weather.
• B. Harmonics are the same as flicker; mitigated by harmonic filters.
• C. Harmonics are caused by temperature fluctuations; mitigated by proper sizing.
• D. Harmonics are multiples of the fundamental frequency caused by non-linear loads; mitigated with filters, phase-shifting, and proper sizing.

Answer: (D)

Harmonics are frequency components that are exact multiples of the system’s fundamental frequency. They show up when non-linear loads—like rectifiers, switch-mode power supplies, and variable-speed drives—draw current in sharp pulses rather than as a smooth sine wave. This creates a distorted current (and sometimes voltage) waveform that can cause overheating, misoperation of equipment, and electrical interference. The best answer notes that harmonics originate from these non-linear loads and that mitigation typically involves filters to block or cancel specific harmonic frequencies, phase-shifting techniques to reduce harmonic interactions in the network, and proper sizing of equipment and conductors to handle the extra current without excessive losses or overheating. Other statements are off the mark: harmonics are not just random noise from weather, and they are not simply the same phenomenon as flicker (though they can interact with it); flicker is about voltage fluctuations that people perceive as light flicker, while harmonics are specific multiple frequencies. Temperature fluctuations don’t create harmonics; they affect resistance and losses rather than the harmonic content of the supply.

Harmonics are frequency components that are exact multiples of the system’s fundamental frequency. They show up when non-linear loads—like rectifiers, switch-mode power supplies, and variable-speed drives—draw current in sharp pulses rather than as a smooth sine wave. This creates a distorted current (and sometimes voltage) waveform that can cause overheating, misoperation of equipment, and electrical interference.

The best answer notes that harmonics originate from these non-linear loads and that mitigation typically involves filters to block or cancel specific harmonic frequencies, phase-shifting techniques to reduce harmonic interactions in the network, and proper sizing of equipment and conductors to handle the extra current without excessive losses or overheating.

Other statements are off the mark: harmonics are not just random noise from weather, and they are not simply the same phenomenon as flicker (though they can interact with it); flicker is about voltage fluctuations that people perceive as light flicker, while harmonics are specific multiple frequencies. Temperature fluctuations don’t create harmonics; they affect resistance and losses rather than the harmonic content of the supply.