Ph.D thesis Defense of Mr.Sounak Nandi

Title of Thesis: Experimental and Theoretical Investigations on High Voltage Polymeric Insulators. 

Research Supervisor:  Subba Reddy B 

Date and Time: Tuesday 24^th Jan 2023, 11am 

Venue: ON Line: Meeting link: 

Abstract 

High Voltage Ceramic and glass Insulators have been widely used by various transmission and distribution utilities for several decades across the globe. Recently composite or silicone rubber insulators have evolved and are now replacing ceramic/glass insulators due to their improved advantages; however, these Insulators suffer from degradation over a period of service.  

The Primary objective of the investigation relates to the study of silicon rubber/polymer insulators under various climatic conditions. Exhaustive experimental studies were conducted to understand the degradation of insulators under different climatic conditions which prevail in the Country.  

Studies on polymer insulators under sub-zero and under extremely high-temperature conditions were attempted experimentally to evaluate their performance. During experimentation, the leakage current was continuously monitored. Later, material analysis, which is a very important aspect and essential to correlate with the morphological changes of the insulator surface, was examined. The experimental investigations demonstrate that there is a need to conduct multi-stress experimentation under specific climatic conditions before the Insulators are installed in the field.  

The next portion of the thesis work deals with the failure mechanism of a Fibre Reinforced Plastic (FRP) Rod. Some portion of the work deals with mathematical analysis being extended to condition monitoring of dielectric surfaces and understanding the performance of FRP rods under high AC voltages. Further, experimental investigations are performed on FRP Rods to analyze the behaviour witnessed, as the field failures reported on Silicon rubber Insulators, interesting results are reported.  

Condition monitoring of dielectric surfaces is very important; hence it was felt necessary to analyze the field performance of transmission/distribution composite Insulators. To understand further, a mathematical analysis based on Chaos has been evaluated for leakage current data and quantization of comparative degradation for a dielectric surface is presented. Later, Empirical Mode Decomposition is also used for understanding leakage current and implied degradation under minimal data conditions. 

Subsequently, the Surface electric field of insulators exposed to HVDC is studied considering the temporal boundary conditions which may arise due to the capacitive-resistive transients. Some experimental investigations are also conducted to compare the simulated results. 

The last portion of the thesis emphases on the study of bulk conductivity of polymer material. The Electric Field dependence of conductivity on the application of voltage and subsequent space charge distribution is attempted.  In short, the thesis work reports some new findings on the experimental, simulation and theoretical studies pertaining to the high voltage polymeric insulators used for EHV/UHV Transmission. 

All are welcome