A new approach for assessing the moisture content in SF 6 -insulated equipment

The moisture assessment of SF 6 -insulated equipment was never a real concern at Hydro-Quebec. In fact, the molecular sieve installed in the equipment was expected to provide an absolute guarantee of the appropriate moisture level. Since then, major failures caused by high moisture content have changed Hydro-Quebec's approach regarding moisture and revealed the importance of its assessment in such equipment. However, from a practical standpoint, there have been problems in accurately assessing the moisture content and then being able to meet the acceptance criteria specified by the manufacturers or by the standards. To prevent new failures associated with high moisture content in SF 6 -insulated equipment, Hydro-Quebec has developed a new approach based on relative humidity measurement. The present paper explains this technical approach, which is supported by outdoor field experiments.