Electric properties of the insulating system change due to age and continuous electrical stress. The principal contributor to the unexpected breakdown of the high voltage equipment is the insulation failure. As compared to the magnetic, conducting and insulating materials which form the basics of any electrical equipment, the insulating material is more prone to service stresses like thermal stress, electric stress, mechanical stress and environment stress etc.

By measuring the electrical properties such as capacitance and Tan Delta regularly on periodical basis, it is possible to ensure the operational unexpected breakdown. Dissipation factor (Tan Delta) is one of the most powerful off-line nondestructive diagnostic tool to monitor the condition of solid insulation of various high voltage equipment.

Capacitance and Tan Delta values obtained on new insulation are treated as benchmark readings. Then by measuring and comparing the periodical readings of the capacitance and Tan Delta of the insulating material with the benchmark readings, one can know the rate of deterioration of the health of the insulation.