The effects of harmonic distortion on equipments

All transformers are affected by harmonics given that any power system is contaminated to some degree by them. What is of interest and concern are the extremes, albeit known and in most cases predictable extremes. Some loads are known as classical harmonic generators so far as transformers are concerned. Any transformer connected to a converter load or an electric arc furnace is by definition connected to a harmonic generator. In the case of the converter harmonic levels maybe variable, predictable and even controllable. In the case of an arc furnace the uncontrolled nature of the arcs during certain times of the melting process produces wholly unpredictable and randomly generated harmonic currents. In order to demonstrate the effects of harmonics on transformers two illustrations are proposed: firstly a case study of what happens when the effects, very regrettably, are not predicted; and secondly how, with modern standards and computer aids, the effects can be predicted, incorporated into the design and demonstrated by appropriate thermal tests