Analysis of harmonic distortion levels on a distribution network

It is generally acknowledged that harmonic distortion levels on distribution networks are steadily increasing due to the proliferation of non-linear loads. While customer complaints relating to harmonic distortion levels are relatively uncommon, and measured levels are typically well within the limits specified by national regulations and international standards, the increasing trend may mean that more active management by utilities will soon be required. Effective management of harmonic distortion levels will require knowledge not only of the level of disturbance, but also of how the disturbance levels vary with time, location, and the connected load. Accepted methods for assessing harmonic levels that rely on cumulative probability statistics are inadequate for this level of insight. In this paper voltage total harmonic distortion levels (THDv) from a distribution network power quality survey are analysed in terms of variation with time, system load and the physical characteristics of the monitored sites.