If damage occurs due to current distortion, except for high neutral current, then one solution is to reduce the distortion. There are three methods for this. First, a passive filter can be used to reduce the current from one or two specific harmonics. In the second method, an active filter reduces all the harmonic currents. It is more costly and complex to use, but it works better than passive filters. The third method involves the use of transformers. Delta-wye transformers reduce certain harmonics, particularly what are called zero sequence harmonics. Zig-zag transformers can also be used to reduce zero sequence harmonics, but without changing the system type between delta and wye. In addition, they can help reduce high neutral currents. If there is concern that these special transformers or the regular distribution transformers may overheat, then transformer derating, or the use of K-rated transformers, is recommended. If high neutral currents are the culprit, then the first step is to eliminate shared neutrals wherever possible. Where this cannot be done, try oversizing the neutral wire so it won't overheat. If this doesn't work, then the distortion must be reduced as described above.
There are two ways to reduce voltage distortion. Remember that internal voltage distortion is the result of the business' non-linear loads interacting with the wiring. The first way to reduce the distortion is to reduce the harmonic current. The second way is to reduce the impedance of the wiring. This is done by increasing the size of the conductors. Where the total voltage distortion is the sum of internal and external distortion, these techniques reduce the internal contribution.
