IEC 60071-1:2011 pdf Insulation co-ordination – Part 1: Definitions, principles and rules
1 Scope
This part of IEC 60071 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.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments) applies.
IEC 60038:2002, IEC standard voltages
IEC 60060-1 :1 989, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60071 -2, Insulation co-ordination – Part 2: Application guide
IEC 60099-4, Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c. systems
IEC 60507, Artificial pollution tests on high-voltage insulators to be used on a.c. systems
IEC 60633, Terminology for high-voltage direct current (HVDC) transmission
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 insulation co-ordination
selection of the dielectric strength of equipment in relation to the operating voltages and
overvoltages which can appear on the system for which the equipment is intended and taking into
account the service environment and the characteristics of the available preventing and
protective devices [IEC 604-03-08:1 987, modified]
NOTE By “dielectric strength” of the equipment, is meant here its rated or its standard insulation level as defined in 3.35 and 3.36 respectively.
3.2 external insulation
distances in atmospheric air, and the surfaces in contact with atmospheric air of solid insulation
of the equipment which are subject to dielectric stresses and to the effects of atmospheric and
other environmental conditions from the site, such as pollution, humidity, vermin, etc.
[IEC 604-03-02:1 987, modified]
NOTE External insulation is either weather protected or non-weather protected, designed to operate inside or outside closed shelters respectively.
3.3 internal insulation
internal distances of the solid, liquid, or gaseous insulation of equipment which are protected from the effects of atmospheric and other external conditions
[IEC 604-03-03:1 987]
3.4 self-restoring insulation
insulation which, after a short time, completely recovers its insulating properties after a
disruptive discharge during test
[IEC 604-03-04:1 987, modified]
NOTE Insulation of this kind is generally, but not necessary, external insulation
3.5 non self-restoring insulation
insulation which loses its insulating properties, or does not recover them completely, after a disruptive discharge during test
[IEC 604-03-05:1 987, modified]
NOTE The definitions of 3.4 and 3.5 apply only when the discharge is caused by the application of a test voltage during a dielectric test. However, discharges occurring in service may cause a self-restoring insulation to lose partially or completely its original insulating properties.
IEC 60071-1:2011 pdf Insulation co-ordination – Part 1: Definitions, principles and rules
