Evaluation of harmonic levels in electrical networks by statistical indexes

The problem of evaluation and forecasting of harmonic pollution levels in power networks supplying many nonlinear power devices is generally solved resorting to the “worst-case” criterion, which consists of the arithmetic sum of harmonic current amplitudes (i.e., in-phase vectorial sum) at network buses. However, due to the fact that harmonics (particularly those of a higher order) may have significantly different phase angles, this assumption has been proven to be too conservative in most practical applications. More realistic evaluations can be obtained by regarding the distorting loads as harmonic-current sources, characterized by probability density functions of both magnitude and phase. In this paper, the problem of harmonic pollution in electrical networks is dealt with using the above-mentioned simplified procedure. In particular, a comparative study is carried out on the effectiveness of these expressions, which have been proposed to simplify evaluation and forecasting of harmonic pollution levels in AC power networks