Study of frequency variant tan delta diagnosis for MV cables insulation status assessment

There is no doubt that the condition or status assessment of the insulation of any medium voltage (MV) cable is essential for the secure and reliable operation of electrical networks. It is reputed that the aging and degradation of the insulation causes severe damage to any MV equipment. Therefore, if these degradations of the insulation can be detected/diagnosed earlier, then corrective action can be initiated. Tan Delta (tan $\delta$) or loss tangent is widely used as a diagnostic method for determining the quality of the insulation in cables. At low-frequency measurements of tan $\delta$ (loss tangent) seem to yield much information about the state of the insulation. Similarly, in some cases frequency higher than 50 Hz or 60 Hz provides useful information about insulation status of MV cables. That is why the values of tan $\delta$ are not strictly constant and but depend on various factors such as frequency, temperature, humidity, and voltage. Thus it is important to understand such relationships by experimental investigations. In this study measurement of tan $\delta$ (TD) at different frequencies (such as 0.01 Hz, 0.1 Hz, 50 Hz, 100 Hz to 400 Hz, etc.) for MV cables will be evaluated. All measurements are taken under standard environmental conditions for new, service old and artificially laboratory aged samples. Finally, the obtained values of tan $\delta$ from the measurements will be analyzed in order to find out if there is any correlation between tan $\delta$ and frequencies (f) with the insulation condition/status under laboratory environment.