TC 28 - Insulation co-ordination

IEC 60071-1:2019 applies to three-phase AC systems having a highest voltage for equipment above 1 kV. It specifies the procedure for the selection of the rated withstand voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment and the installations of these systems. It also gives the lists of the standard withstand voltages from which the rated withstand voltages are selected. This document describes that the selected withstand voltages are associated with the highest voltage for equipment. This association is for insulation co-ordination purposes only. The requirements for human safety are not covered by this document. Although the principles of this document also apply to transmission line insulation, the values of their withstand voltages can be different from the standard rated withstand voltages. The apparatus committees are responsible for specifying the rated withstand voltages and the test procedures suitable for the relevant equipment taking into consideration the recommendations of this document.
NOTE In IEC 60071-2, all rules for insulation co‑ordination given in this document are justified in detail, in particular the association of the standard rated withstand voltages with the highest voltage for equipment. When more than one set of standard rated withstand voltages is associated with the same highest voltage for equipment, guidance is provided for the selection of the most suitable set.
The main changes from the previous edition are as follows:
- all references are updated to current IEC standards, and the bibliography is deleted;
- some definitions are clarified in order to avoid overlapping and ensure clear understanding;
- letter symbols are changed and corrected in order to keep the consistency with relevant IEC standards;
- some titles are changed to clarify understanding (see Clauses A.2, A.3 and Annex B).
It has the status of a horizontal standard in accordance with IEC Guide 108.

IEC 60071-2:2018 constitutes application guidelines and deals with the selection of insulation levels of equipment or installations for three-phase electrical systems. It gives guidance for the determination of the rated withstand voltages for ranges I and II of IEC 60071-1 and to justify the association of these rated values with the standardized highest voltages for equipment. It covers three-phase systems with nominal voltages above 1 kV. This edition includes the following significant technical changes with respect to the previous edition:
a) the annex on clearance in air to assure a specified impulse withstand voltage installation is deleted because the annex in IEC 60071-1 is overlapped;
b) 4.2 and 4.3 on surge arresters are updated;
c) 4.3.5 on very-fast-front overvoltages is revised. Annex J on insulation co-ordination for very-fast-front overvoltages in UHV substations is added;
d) Annex H on atmospheric correction – altitude correction is added.
e) Annex I on evaluation method of non-standard lightning overvoltage shape is added.
It has the status of a horizontal standard in accordance with IEC Guide 108.

Gives guidance on the protection of overvoltage issues for both stand-alone and grid-connected photovoltaic power generating systems.

IEC 60071-1:2006 applies to three-phase a.c. systems having a highest voltage for equipment above 1 kV. It specifies the procedure for the selection of the rated withstand voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment and the installations of these systems. It also gives the lists of the standard withstand voltages from which the rated withstand voltages should be selected. This standard recommends that the selected withstand voltages should be associated with the highest voltage for equipment. This association is for insulation co-ordination purposes only. The requirements for human safety are not covered by this standard. Although the principles of this standard also apply to transmission line insulation, the values of their withstand voltages may be different from the standard rated withstand voltages. The apparatus committees are responsible for specifying the rated withstand voltages and the test procedures suitable for the relevant equipment taking into consideration the recommendations of this standard. NOTE: In IEC 60071-2, Application Guide, all rules for insulation co ordination given in this standard are justified in detail, in particular the association of the standard rated withstand voltages with the highest voltage for equipment. When more than one set of standard rated withstand voltages is associated with the same highest voltage for equipment, guidance is provided for the selection of the most suitable set. The main changes from the previous edition are as follows:
- in the definitions (3.26, 3.28 and 3.29) and in the environmental conditions (5.9) taken into account clarification of the atmospheric and altitude corrections involved in the insulation co-ordination process;
- in the list of standard rated short-duration power frequency withstand voltages reported in 5.6 addition of 115 kV;
- in the list of standard rated impulse withstand voltages reported in 5.7, addition of 200 kV and 380 kV;
- in the standard insulation levels for range I (1kV  - in the standard insulation levels for range II (Um ≤ 245 kV) (Table 3) replacement of 525 kV by 550 kV and of 765 kV by 800 kV;
- in order to remove that part in the next revision of IEC 60071-2, addition of Annex A dealing with clearances in air to assure a specified impulse withstand voltage in installation;
- in Annex B, limitation at two Um values for the values of rated insulation levels for 1kV  It has the status of a horizontal standard in accordance with IEC Guide 108.

Gives guidance on conducting insulation co-ordination studies which propose internationally recognized recommendations - for the numerical modelling of electrical systems, and - for the implementation of deterministic and probabilistic methods adapted to the use of numerical programmes. Its object is to give information in terms of methods, modelling and examples, allowing for the application of the approaches presented in IEC 60071-2, and for the selection of insulation levels of equipment or installations, as defined in IEC 60071-1.

IEC 60071-2:1996 gives guidance for the determination of the rated withstand voltages for ranges I and II of IEC 60071-1 and justifies the association of these rated values with the standardized highest voltages for equipment. It covers phase-to-phase, phase-to-earth and longitudinal insulation of three-phase systems with nominal voltages above 1kV. It has the status of a horizontal standard in accordance with IEC Guide 108.