Preventing Failures in Outdoor Distribution-Class Metalclad Switchgear

Failure of the insulation in distribution-class metalclad switchgear may release large amounts of energy resulting in an explosive hazard to adjacent equipment and personnel. Many such failures have occurred in older outdoor and generating station switchgear within Ontario Hydro. The failures have often been caused by partial discharge (PD) activity and surface tracking which destroy organic bus support insulation. Test methods have evolved to help locate deteriorating insulation in the field, and to qualify new insulation systems. The life of the switchgear can often be extended by incorporating appropriate preventive maintenance. To improve our ability to locate deteriorating switchgear insulation economically, a prototype continuous monitoring system has been developed which is sensitive to partial discharges, thus allowing plenty of warning (usually several years) that the insulation system may be in trouble. The probability of ``false alarms´´ from this system has been greatly reduced by monitoring both acoustically and electrically simultaneously. Tests in two metalclad switchgear installations have shown the system to be immune to extraneous noise, while maintaining sensitivity to partial discharges. The installation of the monitoring system in stations prone to insulation problems enhances the reliability and safety of metalclad switchgear, and greatly reduces repair costs.