Harmonic Solutions
Being the third in a three part series of harmonics, this will cover potential solutions for harmonics. A bit of information to be aware of when dealing with harmonics and attempting to find solutions for them. There is no fast and quick solution for harmonics, no one size fits all type of solution. Each installation is different, and even though they may have the same harmonics, the sources and solutions could be different. Before attempting any type of harmonic mitigation, a full analysis should be performed, and a determination should be made on which harmonics need mitigation, would it be better to replace the “offending” equipment, or should nothing be done at all.
Active Filter
Active filters are a unique type of power electronic solution to mitigating harmonics. Depending on the manufacture and the brand of filter, there are a couple of ways they can be installed and utilized. On an overall synopsis, they monitor the voltage and current, and create an inverse wave of equal magnitude to cancel the harmonics on the system. They can be installed in series or in parallel, depending on the type of load, the magnitude of the harmonics, and the desired outcome. What sets the active filter apart from other forms of mitigation is there is an internal processor monitoring the waveform in real-time and actively correcting the wave-shape.
Passive Filter
A more well-known solution is a passive filter. A passive filter is usually a tuned reactive circuit that is designed to eliminate or drastically reduce a specific harmonic component. By tuning a LC circuit to a specific harmonic frequency, the passive filter creates a low impedance path for the harmonic to flow through. Unlike active filters, passive filters will typically target one harmonic, and has no power electronics on board for active measurements.
Neutral Current Filter
Since currents that flow through the neutral conductor can create overheating due to under sized wire, using a neutral current filter makes sense. The filter itself is designed to eliminate or reduce triplen harmonics, or zero sequence harmonics.
Zig Zag Transformer
This method reduces 5th and 7th, and depending on how it is installed, can also trap triplens inside the windings of the transformer. By utilizing phase shifting in a three phase transformer that is designed with a low zero sequence impedance, and installing it in parallel with the load, a zero sequence current path is created, which eliminates the triplens.
The four listed above solutions are just a few means to mitigate harmonics. As mentioned before, there is no one size fits all solution; however understanding how they can be mitigated can help spearhead an investigation into what outcome is most desired.
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