Insulators for overhead lines - Composite suspension and tension insulators for a.c. systems with a nominal voltage greater than 1 000 V - Definitions, test methods and acceptance criteria

IEC 61109:2025 applies to composite insulators for overhead lines consisting of a load-bearing cylindrical insulating solid core consisting of fibres - usually glass - in a resin-based matrix, a housing (surrounding the insulating core) made of polymeric material and metal end fittings permanently attached to the insulating core. Composite insulators covered by this document are intended for use as suspension/tension line insulators, but these insulators could occasionally be subjected to compression or bending, for example when used as interphase-spacers. Guidance on such loads is outlined in Annex C.

The object of this document is to:

- define the terms used,

- specify test methods,

- specify acceptance criteria.

This third edition cancels and replaces the second edition published in 2008. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous edition:

- extension of this document to apply both to AC and DC systems;

- modifications of Clause 3, Terms, definitions and abbreviations;

- removal of Clause 7, Hybrid insulators, from this document;

- modifications of tests procedures recent