Degradation Studies on Polymeric Insulators used for EHV and UHV Transmission

Abstract

High voltage insulators used in overhead power transmission systems are of key im- portance for safe, reliable, and effcient operation of transmission line in transferring huge amount of electrical power. Conventionally, ceramic/ glass insulators were used in electri- cal power transmission, recently composite/ polymeric insulators are being used in over- head transmission lines. The polymeric insulators offer numerous promising advantages over conventional insulators such as light weight, higher impact strength, better pollution performance, resistance to vandalism due to its slim design etc. Moreover, the inherent property of polymeric insulators of being hydrophobic make it more advantageous over conventional insulators. However, the polymeric material being organic in nature, un- dergo degradation due to different stresses such as environmental stresses (thermal, UV, moisture, fog etc,), and electrical stresses. Further, the presence of electrical discharges such as corona, surface scintillations, occurrence of dry band arcing, operation in adverse conditions, etc., are recognized as the major accelerating factors for material degrada- tion. Presence of heavy ionic deposition over the surface leads to surface discharges and localized temperature rise leads to material erosion which results in electrical tracking formation and eventually leads to ash-over/ line outage of power transmission. In the present work, silicone rubber based polymeric insulators are experimentally in- vestigated for their material properties and long-term service performance. The available literature show that polymeric insulators are quite sensitive to their local environmental conditions and their long-term performance depends on field service environment. The material properties get affected in adverse environment and foul weather condition. The unavoidable service conditions such as moisture, fog, acidic rain, snow, pollution etc., alter their service life by accelerating their aging which directly affect their long-term performance. The evaluation of material properties such as surface electrical resistance and long-term performance of these composite insulators are still under consideration. The present thesis work focuses on the study of majorly two aspects of polymeric insulators which governs its performance in service life. One of them is the material prop- erty, which provides the surface electrical resistance; important role in avoiding the surface electrical tracking in the polymeric insulators under polluted/ contaminated conditions. The second aspect is the long-term performance analysis. In the first part of the thesis work, the experimental investigation are conducted using indigenously developed experi- mental arrangements. The investigation pertaining to surface resistance of silicone rubber insulating material investigations, Inclined plane tracking and erosion (IPT) method is utilized. The evaluation of the material property is conducted under different environ- mental condition simulating as per standard (normal condition) and acid rain condition under AC and DC voltage application. The acidity value and salt contents of artifi cial acid rain is simulated based on the physically observed acid rain information. In summary, the main contribution of present work is to understand the effect of different environmental condition on the degradation of silicone rubber insulators and its effect on material properties and long-term performance. Recurrence plot analysis performed on measured leakage current present the visual pattern that provide clear discrimination between fresh and degraded sample. It is proposed that this method could be used as an important tool to detect and diagnosis the loss of material property of polymeric insulators. The investigation presents more realistic contribution towards the surface degradation studies on Polymeric Insulators used for EHV and UHV Transmission.