Draft Guide for Harmonic Limits for Single-Phase Equipment

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Guide for Harmonic Limits for Single-Phase Equipment
  1. Overview

The growth in power electronics has impacted many loads that traditionally were considered linear in nature. As a result, the number of nonlinear loads has increased and is expected to increase dramatically in the years ahead.

High harmonic content should be regarded as an undesirable load characteristic much like low power factor or low efficiency. With each of these, it’s a matter of degree. While some can be tolerated, an excessive amount should be avoided.

Although the number of problems caused by harmonics is not yet a significant widespread problem, the potential for such problems is much greater today than it was 10 years ago, and the effects of nonlinear loads are becoming an increasing concern in many parts of the world today. In addition, single-phase converters, found in many devices, have particularly high amounts of all odd harmonics, particularly the third harmonic.

A variety of single-phase equipment can be categorized as nonlinear today. Switch-mode power supplies are found in a variety of devices like computers, televisions, VCRs, etc. Compact fluorescent lamps are now available with electronic ballasts. Variable speed control is evolving to include washers, dryers, space heating and air-conditioning. Battery chargers are being developed for electric and hybrid-electric vehicles, and the list continues.

There have been a number of different studies which investigated one of these new technologies to see if and when a potential problem might surface on the distribution system due to single-phase harmonic sources. For the most part, these studies did not consider these loads in combination.

What we find is found is a wide range of nonlinear devices that have been identified which collectively need to be considered for future power distribution systems. In addition, there are some newer technologies being explored which could add to the previous mix.

The objective is to arrive at a reasonable set of limits for single-phase equipment such that the likelihood of a problem caused by harmonics is small.

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