2 Solid Insulation

Solid Insulation is defined as insulation consisting entirely of solid material. The intrinsic material characteristics of solid insulation directly impact its insulation behavior. As the electric strength of solid insulation is considerably greater than that of air, the distances through solid insulation are much smaller than the clearance so that high electric stresses result. In insulation systems, gaps or voids may occur between electrodes and insulation and between different layers of insulation. Partial discharges can occur in these voids at voltages far below the level of puncture and this influences the service life of the solid insulation. As opposed to air, solid insulation is not a renewable insulating medium and therefore high voltage peaks which may occur infrequently can have a very damaging and irreversible effect on solid insulation. This situation can occur while in service and during routine high-voltage testing. The physical and geographical location of the equipment can affect the insulation system significantly. Environmental factors such as altitude, temperature, vibrations and humidity require consideration to ensure that the insulation remains reliable over the life time of the equipment.