6.3.1 On utility distribution feeders

The X/ R ratio of a utility distribution feeder is generally low. Therefore, the magnification of harmonics by resonance with feeder banks is usually minor in comparison to what might be found inside an industrial facility. Utility distribution engineers are accustomed to placing feeder banks where they are needed without concern about harmonics. However, voltage distortion from the resonance of feeder banks may exceed limits in a few cases and require mitigation. When problems do occur, the usual strategy is to first attempt a solution by moving the offending bank or changing the capacitor size or neutral connection.

Some harmonic problems associated with feeder capacitor banks are due to increasing the triplen harmonics in the neutral circuit of the feeder. To change the flow of zero-sequence harmonic currents, changes are made to the neutral connection of wye-connected banks. To block the flow, the neutral is allowed to float. In other cases, it is more advantageous to aid the flow by putting a reactor in the neutral to convert the bank into a tuned resonant shunt for a zero-sequence harmonic.

Harmonic problems on distribution feeders often exist only at light load. The voltage rises, causing the distribution transformers to produce more harmonic currents and there is less load to...