Rectifier input current distortion-how much can be permitted? Implications of existing standards and other considerations

Harmonic pollution of electrical power systems is a subject of increasing importance. Power converters are a type of load that generates current harmonics, and the designers of converter equipment are highly concerned with this problem. Two existing standards, the European EN 60 555-2 and the American IEEE Std 519 formulate the requirements on harmonic contents. This paper analyses these standards and their practical implications. It is shown that (a) there is a certain ambiguity in applying EN 60 555-2, (b) although IEEE 519 refers to the power system, not to the equipment, it is possible-by some additional analysis-to formulate the requirements on the AC/DC converter equipment, and (c) despite the differences in the approach, both standards result in similar requirements. Additional considerations are necessary to determine the allowable distortion values. One such consideration is the case of supply from an emergency set diesel engine alternator. Any rectifier design should consider the eventuality of supply from an emergency set of limited power rating. The emergency set is a soft source with high internal impedance. In this case rectifier current harmonics can cause excessive voltage harmonics in the AC distribution, resulting in a severe degradation of service. This paper describes a procedure to determine the permissible requirements on voltage quality-including the case of emergency set supply. On the basis of this analysis, a value of allowable input current distortion is proposed