S. Chandrasekar

A Random Forest Model Based Pollution Severity Classification Scheme of High Voltage Transmission Line Insulators

Tower insulators in electric power transmission network play a crucial role in preserving the reliability of the system. Electrical utilities frequently face the problem of flashover of insulators due to pollution deposition on their surface. Several research works based on leakage current (LC) measurement has been already carried out in developing diagnostic techniques for these insulators. Since the LC signal is highly intermittent in nature, estimation of pollution severity based on LC signal measurement over a short period of time will not produce accurate results. Reports on the measurement and analysis of LC signals over a long period of time is scanty. This paper attempts to use Random Forest (RF) classifier, which produces accurate results on large data bases, to analyze the pollution severity of high voltage tower insulators. Leakage current characteristics over a long period of time were measured in the laboratory on porcelain insulator. Pollution experiments were conducted at 11 kV AC voltage. Time domain analysis and wavelet transform technique were used to extract both basic features and histogram features of the LC signal. RF model was trained and tested with a variety of LC signals measured over a lengthy period of time and it is noticed that the proposed RF model based pollution severity classifier is efficient and will be helpful to electrical utilities for real time implementation.

Analysis of Partial Discharge Signal Characteristics of Nano-Mineral Oil for Transformer Condition Monitoring Applications

Transformer is an expensive and key component in an electric power transmission network. Most of the failure of transformer occurs due to degradation of insulation oil, which further leads to major economical losses and power shutdown. Advancements in nanotechnology has given horizons for the development of nanofluids for transformer insulation applications. Understanding the enhancements in dielectric properties of nanofiller added mineral oil is a hot research area. In recent times, partial discharge (PD) detection and analysis is a well recognized insulation condition monitoring technique for transformers. However, reports on PD signal characteristics of nano filler added mineral oil is scanty. This paper attempts to investigate the PD characteristics of SiO2 nanofiller added mineral oil at different %wt concentrations of nanofiller material. Major PD source normally experienced in transformers i.e. corona discharge due to non-uniform electric field was simulated in the laboratory using needle-plane electrode configuration and the corresponding PD signals were measured using wide band PD detection system. Important PD characteristics such as inception voltage, stable PD formation voltage, PD amplitude with respect to increase in voltage stress and PD signal frequency spectrum were evaluated. Results clearly show that addition of SiO2 nanofiller material in the base mineral oil enhances PD performance of mineral oil and these results will be useful for electrical utilities for developing effective condition monitoring system for transformers.

Chemical Reaction Effects Past an Exponentially Accelerated Isothermal Vertical Plate with Uniform Mass Diffusion in the Presence of Magnetic Field and Hall Currents

Successful operation of electric power transmission and distribution network depends on the consistency of power transformers. Any unscheduled outage due to a faulty transformer leads to expensive and time consuming repair work and affects the entire power system reliability. Majority of the power transformer faults occur due to aging and degradation of oil insulation. Mineral oil is being used as a liquid dielectric in transformers for a longer period of time. In general, periodic monitoring of electrical, physical and chemical properties will certainly give information about the aging and deterioration of insulating oil. In recent times, advancements in nanotechnology has given scope for the development of nano-dielectrics for transformer insulation applications. Many research works are being carried out to understand the dielectric performance enhancements in nano-modified insulating oils for high voltage applications. In the present work, dielectric properties of nano-SiO2 modified mineral oil is investigated. Detailed reports on the characteristics of nano SiO2-modified mineral oil such as breakdown strength, loss factor, volume resistivity, viscosity, flash point and fire point are scanty. Hence, this paper attempts to investigate the above mentioned characteristics of SiO2 nanofiller added mineral oil at different %wt concentrations of nanofiller material. Results clearly show that addition of SiO2 nanofiller material in the base mineral oil enhances dielectric performance of mineral oil. These results will be useful for electrical utilities in improving the design aspects, identifying the root cause of insulation failures and carrying out the preventive maintenance activities of transformers.

Investigations on Dielectric Performance Characteristics of Natural Ester based Nano-Fluids for Power Transformer Applications

Liquid insulation for high voltage transformer applications based on natural esters derived from abundantly available vegetable oils are becoming popular in recent times. Since these natural ester based oils have environmental advantages and superior thermal performance, electrical utilities are slowly replacing the conventional mineral oils with natural ester based vegetable oils. FR3 oil, which is a soya based natural ester oil with superior dielectric and thermal characteristics, is becoming popular as an alternate insulating medium for high voltage transformers. With recent developments in nanotechnology field, it is possible to enhance the dielectric performance characteristics of natural ester based oils, which is a major constraint for high voltage transformer applications. However few research reports are only available in the area of nanofluids based on natural esters for high voltage insulation applications. In depth analysis and collection of large data base of insulation performance of natural ester based vegetable oils is important to improve the confidence level over nano-fluids based on natural esters. Considering these facts, in the present work, dielectric properties such as breakdown strength, capacitance, tan delta, relative permittivity and volume resistivity of nano-SiO2 modified FR3 oil are investigated at different %wt filler concentrations. From the results, it is observed that the dielectric performance of FR3 oil is significantly improved with the addition of nano-SiO2 filler. Since in recent times FR3 oil is commercially used in many transformers, these results will be useful for enhancing the dielectric strength of high voltage transformers.

Analysis of Electrical Tree Inception and Propagation in XLPE Nano-Composites

In this present work, electrical treeing analysis of the virgin and nano size filled Cross Linked Polyethylene (XLPE) material has been studied. Silicone Oxide (SiO2)nano-filler was used in the XLPE base material. Nano-fillers were added at 1% concentration by weight in the base material. Laboratory experiments were conducted as per IEC procedures at 12 kV AC voltage. Influence of filler concentration on the inception and propagation of electrical treeing were studied. Analysis of time to failure of XLPE materials at 1%nano-filler concentrations were carried out. Tensile strength were measured for understanding the mechanical properties of the nano filled XLPE material, Scanning Electron Microscope (SEM) carried out for understanding the dispersion of nano fillers in the nano filled XLPE material.

Analysis of Water Treeing Resistance Performance Characteristics of Nano Filled XLPE Cable Insulating Material

In recent times, high voltage secondary distribution network in urban areas is widely supported by XLPE cables because of its advantages over conventional overhead lines. Major problem faced in the usage of underground cables is the failure of insulation due to water treeing phenomena. It occurs mainly due to water diffusion in the base XLPE polymeric material leading to the breakdown of cable insulation over a period of time. As a result of water treeing, dielectric strength of the material reduces significantly. Recent advancements in nanotechnology shows that addition of nanofillers in the base polymeric material will enhance the thermal and electrical insulation characteristics of the material. However, very few reports are only available in the literature regarding the water treeing resistance characteristics of nano-modified XLPE material. Hence it is necessary to perform a variety of tests on nano-modified XLPE material in order to collect a large volume of data useful for electrical utilities. Considering these aspects, in this paper, important dielectric performance characteristics of nano SiO2 filled XLPE material such as dielectric constant, tan delta, volume resistivity and capacitance are studied at different %wt concentration of nano-filler. In addition, laboratory experiments were also carried out in order to understand the water treeing resistance characteristics of nano filled XLPE material under virgin and aged conditions.