Porcelain — A modern insulation for metal-clad switchgear

The trend in switchgear insulation has been toward materials having higher operating temperatures, greater arc and track resistance, improved mechanical properties, and being readily producible in the sizes and shapes required. This trend has been dictated by expanding loads resulting in continuous operation at or near rated current, changes in load patterns resulting in the heaviest loads being carried on the hottest days and increased loading of individual units resulting in greater dependence on each unit. To achieve its performance objectives switchgear must operate at a high level of reliability.