Effects of switch mode power supply harmonic currents on building power systems and stand-by engine alternators

Power supplies drawing high peak currents are very common in today´s buildings. These high peak currents contain the odd harmonics, and of special interest are the triplen harmonics-3, 9, 15, etc. Small power supplies are commonly connected from phase to neutral of the typical building power system. Engineers commonly distribute the loads among the phases to balance the building loads. However, they often over-look the effects of the third order harmonics on neutral current, expecting the phase currents to partially cancel in the neutral. The third order harmonics add and can lead to very high neutral currents. The high currents may cause excessive heating in the neutral conductor. In addition the high peak currents can have an adverse effect on the output wave shape of stand-by engine alternators