Proceedings of the 2019 5 th International Conference on Advances in Electrical Engineering (ICAEE), 26-28 September, Dhaka, Bangladesh. 978-17281-4934-9/19/$31.00©2019 IEEE Study of frequency variant tan delta diagnosis for MV cables insulation status assessment Md Zulfiker Heider Electrical Engineering Department King Saud University Riyadh, Saudi Arabia heidereee@gmail.com Mohammad Mominur Rahman Department of Electrical & Electronic Engineering Ahsanullah University of Science & Technology Dhaka, Bangladesh. momin128@gmail.com A. A. Al-Arainy Electrical Engineering Department King Saud University Riyadh, Saudi Arabia aarainy@ksu.edu.sa Abstract— 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 δ) 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 δ (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 δ 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 δ (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 δ from the measurements will be analyzed in order to find out if there is any correlation between tan δ and frequencies (f) with the insulation condition/status under laboratory environment. Keywords—MV cables, Loss tangent, Insulation degradation. I. INTRODUCTION The insulation of any high voltage equipment is usually made up of different components. These components are selected to withstand different electrical, mechanical, thermal, and environmental stresses. In the past, functional evaluation of insulation was based primarily on thermal stresses. However, with many types of equipment, other aging stresses or factors, such as mechanical, electrical, and environmental may also be dominant and could significantly influence the service life of the insulation [1-6]. Effective and reliable insulation is essential for the correct and safe operation of any electrical equipment. In MV systems, protection testing is considerably increasingly significant, on the grounds that the protection is frequently under more prominent electrical pressure. Therefore, failures are likely to be costlier and potentially more dangerous in such systems compare to low voltage systems. Recently several insulation testing techniques such as RVM (Recovery Voltage Method), PDC (Polarization and Depolarization Currents) and tan delta (tan δ) method. have been developed. Every method has some advantages and disadvantages. Similarly, there are many advantages of tan δ method for insulation condition assessment. But the most important thing is ease of use of tan delta diagnostic system in field levels. [9]. Several investigations have been made to find out the effect of voltage, frequency, and temperatures in tan δ (TD) measurements. Yakun et al. [1] showed the influence of the temperature and frequency on leakage current of XLPE cable. He found the cable conductivity is high at low frequency and at high temperature. At high frequency, cable conductivity did not affect that much with the increase of temperature in XLPE cable. Kocatepe et al. [2] mentioned the dissipation factor and dielectric losses increase with the increase of voltage. But the variation of tan δ for certain smaller increases i.e. for 2- 4 kV deviation at the beginning is not that much. But when the voltage increases to 8kV and higher, then tan values increase significantly. And these measurements were taken at 50 Hz frequency. Chandan Kumar Chakrabarty et al.[3] developed a high- frequency tan delta testing method for underground cable. Then they tested some good cables, contaminated cables and void cables at 50 Hz and 1 kHz. They showed a correlation between tan delta with 50 Hz and 1 kHz using normalization from the obtained tan delta values of their experiments. Belle Valerie Wong et al.[7] investigated VLF tan delta(TD) and PD measurement in MV cables. They found that VLF TD (tan δ) measurement is useful and reflects the overall condition of the cable as well as to indicate the presence of wet joints and water tree aging. J. C. Hernández-Mejía et al. [6] did experiment to find out the correlation between tan δ Diagnostic Measurements and Breakdown Performance at VLF for MV XLPE Cables. They used 0.1 Hz and 60 Hz frequency test voltages for their findings. They successfully presented the co-relation with tan delta and breakdown. 