Electrical properties of the insulating system change due to age and continuous electrical street. The principal contributor to the unexpected breakdown of the high voltage equipment is the insulation failure.
As compared to the magnetic, conducting & insulating materials which form the basics of any electrical equipment, the insulating material is more prone to service stresses like thermal stress, electrical stress, mechanicals stress, 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.
Knowing the rate of deterioration, we can be able to Predict the future unexpected breakdown of the insulation of HV equipment. Plan the maintenance schedule. Repair the insulation before actual flashover, saving high cost of replacement of material which will reduce the inventory well as delay in procurement at the last minute.
After repair, quality of insulation can be checked before returning the equipment to service. When to check capacitance & Tan-Delta During manufacturing process preferably at each stage. In service & will be depend on rate of change of Tan-Delta Vs Voltage Vs Time (Month/Year).
Frequency of testing depends on history of past failures on same machine. Frequency of testing depends on environmental conditions. More humidity, temperature, pollution would require frequency measurement of Tan-Delta.
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