Design Calculators - Electrical

Tips for Reducing Harmonic Distortion

High levels of harmonic distortion can lead to increased energy losses, equipment overheating, premature aging of insulation, and interference with sensitive electronic devices. Here are some effective strategies to mitigate harmonics:

• Passive Harmonic Filters: These are combinations of inductors (reactors) and capacitors tuned to resonate at specific harmonic frequencies, providing a low-impedance path for harmonic currents, diverting them from the supply. They are relatively inexpensive but can be bulky and their effectiveness depends on the stability of system impedance.
• Active Harmonic Filters (AHF): These are advanced electronic devices that inject compensating currents into the system to cancel out harmonic currents generated by loads. AHFs are more flexible, can adapt to varying load conditions, and are generally more effective than passive filters, especially for dynamic loads and multiple harmonic orders.
• Line Reactors/Chokes: Installing line reactors (inductors) in series with non-linear loads (like VFDs, rectifiers) helps to increase the impedance seen by harmonic currents, thereby reducing the amount of harmonic current drawn from the supply. This is a simple and cost-effective first step for many applications.
• Multi-Pulse Rectifiers (e.g., 12-pulse, 18-pulse drives): For large variable frequency drives (VFDs) and other high-power non-linear loads, using rectifiers with a higher number of pulses (e.g., 12-pulse or 18-pulse instead of 6-pulse) significantly reduces characteristic harmonics (like 5th and 7th).
• K-Rated Transformers: In systems with high harmonic content, standard transformers can overheat due to additional eddy current losses. K-rated transformers are specially designed to handle harmonic currents without excessive heating, improving reliability and efficiency.
• Proper Sizing and Wiring: Ensuring conductors are adequately sized for RMS currents (which are higher with harmonics) and proper grounding can help prevent overheating and minimize harmonic-related issues. Avoiding parallel neutral conductors for 3rd harmonics in 4-wire systems is also critical.

The choice of harmonic mitigation strategy depends on the magnitude and nature of the harmonics, the sensitivity of the connected equipment, and economic considerations. A detailed power quality study by a qualified engineer is recommended for complex systems.