Composite insulators - Hollow insulators for use in outdoor and indoor electrical equipment - Definitions, test methods, acceptance criteria and design recommendations
This technical report applies to composite hollow insulators consisting of a load bearing insulating tube made of resin impregnated fibres, a housing (outside the insulating tube) made of elastomeric material (for example silicone or ethylene-propylene) and metal fixing devices at the ends of the insulating tube. Composite hollow insulators as defined in this report are intended to be used under conditions involving internal pressure or free of pressure. They are intended for use in outdoor or indoor electrical equipment operating on alternating current with a rated voltage greater than 1 000 V and a frequency not greater than 100 Hz or for use in direct current equipment with a rated voltage greater than 1 500 V.
The object of this report is:
- to define the terms used;
- to prescribe test methods;
- to prescribe acceptance criteria.
This report does not prescribe impulse voltage or power frequency voltage type tests or pollution tests because the withstand voltages are not characteristics of the hollow insulator itself, but of the apparatus of which it ultimately forms a part.
NOTE 1 - "Internal pressure" means a permanent gas pressure greater than 0,05 MPa (0,5 bar) gauge. The gas can be dry air or inert gases, for example sulphur hexafluoride, nitrogen, or a mixture of such gases.
NOTE 2 - "No internal pressure" means a gas or liquid pressure smaller than or equal to 0,05 MPa (0,5 bar) gauge. Where hydrostatic pressure exceeds 0,05 MPa different test procedures may be agreed.
NOTE 3 - Composite hollow insulators are intended for use in electrical equipment, such as, but not limited to
· circuit breakers;
· switch-disconnectors;
· disconnectors;
· earthing switches;
· instrument- and power transformers;
· bushings.
Additional testing defined by the relevant IEC equipment committee may be required.