Executive Summary : | Accuracy and reliability of non-invasive diagnostic techniques (based on analysis of dielectric response) cannot be ensured for oil-paper composite insulation system employing alternate dielectric liquid like MIDEL 7131/ Envirotemp FR3 (in pure form or with nano-chemicals) without considering the influence of trapped charges (generated by various sources).
Results obtained using commercially available non-invasive measurement based equipment (like IDAX, DIRANA) are practically accepted by utility providers. Such equipment are designed keeping in mind about properties of oil-paper insulation (which employs mineral oil as primary liquid insulation) and works primarily by analyzing (time or frequency domain) insulation response. Findings reported by investigators of this project prove that presence of charge inside insulation, irrespective of source, alters profile of both time and frequency domain insulation response. Furthermore, it is known that properties of alternate liquid insulation (like MIDEL 7131 synthetic ester) are significantly different than mineral oil. As equipment like IDAX, DIRANA are intended to be used for analysis of response measured from (charge free, mineral-oil based) insulation that is at equilibrium, presence of trapped charge and/or alternate dielectric liquid complicates the matter. This in turn makes result obtained using such equipment doubtful if not inaccurate.
When influence of trapped charge cannot be avoided and alternative dielectric liquids (in pure or nano-fluid form) are used as primary liquid insulation, such equipment either needs to be re-calibrated or its result re-interpreted. Above mentioned re-interpretation of result is possible only when knowledge about effect of trapped charge on insulation response in presence of alternative dielectric liquids are known fully. The above discussion suggests that the research findings of the project are not only crucial for better understanding of insulation response but are also equally important for utilities who are presently using costly commercial equipment. |