This Standard outlines principles which are intended to be used as the basis for determining the requirements for connecting large distorting loads (producing harmonics and/or interharmonics) to public power systems. The primary objective is to provide guidance for engineering practices which will ensure adequate service quality for all connected consumers. Since the guidelines outlined in this Standard are necessarily based on certain simplifying assumptions, there is no guarantee that this approach will always provide the optimum solution for all harmonic problems. The recommended approach should be used with flexibility and judgement as far as engineering is concerned, when applying the given assessment procedures in full or in part. The final decision regarding the connection of distorting installations will always rest with the utility. Problems related to harmonics fall into two basic categories: – The harmonic currents are injected into the supply network by converters and other harmonic sources. Both harmonic currents and resulting voltages can be considered as conducted phenomena. The objective of this Standard is to limit actual harmonic voltages on supply systems to levels (compatibility levels) that will not result in adverse effects on sensitive equipment. Since the harmonic voltages result from harmonic currents and impedances, this involves limiting the harmonic currents injected into the system. – The harmonic currents in the range 50 Hz to 5 kHz may induce interference into communication systems. This phenomenon is more pronounced at higher order harmonic frequencies because of increased coupling between the circuits and because of the higher sensitivity of the communication circuits in the audible range. This Standard primarily focuses on controlling or limiting harmonic voltages and their effects, but a clause is included to address communication interference. Appendices A, B, C, D, E, F, G, H, I, J and K are for information only. NOTES 1 The load is to be understood as the complete consumer’s installation. 2 This Standard uses the following terms for system voltage:– low voltage (LV) refers to Un <= 1 kV;– medium voltage (MV) refers to 1 kV < Un <= 35 kV;– high voltage (HV) refers to 35 kV < Un <= 230 kV;– extra high voltage (EHV) refers to 230 kV < Un.In the context of this Standard, the function of the network is more important than its nominal voltage. For example, a HV system used for distribution may be given a "planning level" (see clause 3) which is situated between those of MV and HV systems. 3 A list of principal letter symbols, subscripts and symbols is given in appendix J.