Insulation co-ordination. Application guidelines

2Scope / Description

Scope This document forms part of IEC 60071 and provides application guidance for the selection of insulation levels for equipment or installations on three-phase electrical systems. Its purpose is to provide guidance on the determination of the rated withstand voltages of IEC 60071-1 for classes I and II and to explain that the purpose of relating these ratings to the maximum voltage standardized in the system is for insulation coordination purposes and not for human safety requirements. The document covers three-phase systems above 1 kV. The results or recommendations presented here are generally applicable only to such systems, but the concepts presented are equally applicable to two-phase or single-phase systems. The document deals with phase-to-earth, phase-to-phase and longitudinal insulation and does not cover routine tests, the requirements of which are determined by the relevant product committees. The content of this document closely follows the insulation coordination flow chart shown in Figure 1 of IEC 60071-1:2006. Clauses 4 to 7 correspond to the boxes in the flow chart and provide specific information on the concepts for determining the required withstand voltage. In addition, at the final stage, when the standard withstand voltage is selected, this document points out the principles for relating the standardized insulation levels and the maximum voltage of the equipment in IEC 60071-1. The appendices include illustrations and explanations or support for the concepts described in the main text and the basic analytical techniques used.