Influence of single and multiple dry bands on critical flashover voltage of silicone rubber outdoor insulators: simulation and experimental study

Dry band formation on the surface of outdoor insulators is one of the main reasons leading to flashover and power outages. In this paper, a dynamic arc model is proposed for single and multiple dry bands configuration to predict the critical flashover voltage for silicone rubber outdoor insulators. An arc is modelled as a time dependent impedance consisting of a Resistor Inductor Capacitor (RLC) circuit. The effect of dry band location and existence of multiple dry bands on critical flashover voltage is investigated. To validate the proposed model, experiments were conducted in a climate chamber under controlled environmental conditions on rectangular silicone rubber sheets polluted using improved solid layer method based on IEC 60,507. Tests were conducted at different dry band configurations and pollution severity levels. A good correlation was found between experimental results and simulation results. This model can provide a good foundation for the development of mathematical models for station post insulators having multiple dry and clean bands and can be used in the design and selection of outdoor insulators for polluted conditions

Electrical Circuit Flashover Model of Polluted Insulators under AC Voltage Based on the Arc Root Voltage Gradient Criterion

In order to study the flashover mechanism of polluted insulators under AC voltage, a new arc propagation criterion which is based on an arc root voltage gradient is proposed. This criterion can explain the variation of the arc root voltage gradient in the arc propagation process. Based on this criterion, a new distributed parameter electrical circuit flashover model of polluted insulators is presented. The arc channel is considered as an equivalent distributed parameter circuit model instead of using the arc voltage-gradient equation. The parameters of the arc model are obtained from the electromagnetic field distribution of the arc and the gas discharge theories. The arc root is considered as parallel paths including the polluted layer. The variation of the voltage on the arc root is related to the capability of arc propagation. This model takes the microscopic mechanism of arc root ionization into consideration, which can improve the accuracy of the flashover model. The results obtained from the presented model are in good agreement with other mathematical and experimental results.National Basic Research Program of China (973 Program) (2009CB724507)National 111 Project of China (B08036

Silicone rubber insulators with notched surface

A modification of an insulator profile was proposed and the advantage of a new solution was shown. The pollution flashover voltage of an insulator with small notches is about 25% higher than the flashover voltage of a flat surface. The laboratory and field tests which show the effectiveness of surface modification made on silicone rubber were described. The possibility of further surface optimization was claimed

Modeling Flashover of AC Outdoor Insulators under Contaminated Conditions with Dry Band Formation and Arcing

abstract: This paper presents a theoretical model for evaluating flashover performance of insulators under contaminated conditions. The model introduces several new features when compared with existing models such as, the formation of dry bands, variations in insulator geometry and surface wettability. The electric field distribution obtained from software for 3-Dimensional models along with form factor are used to determine the dimensions of the dry bands and the onset of arcing. The model draws heavily from experimental measurements of flashover voltage and surface resistance under wet conditions of porcelain and composite insulators. The model illustrates the dominant role played by the insulator shape and housing material on the flashover performance.Dissertation/ThesisM.S. Electrical Engineering 201

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Flashover Voltage Prediction Models under Agricultural and Biological Contaminated Condition on Insulators

The flashover performance of contaminated insulators highly depends on the type of pollutant and its present concentration. In this paper, important agricultural salts (NaCl, K2SO4, NaHCO3, CaSO4, KHCO3, MgSO4, NH4), 2Fe (SO4)2 , 6H2O (ferrous ammonium sulphate, dust and urea) at different concentration and biological contaminants such as algae and fungi were taken as pollutants, and AC flashover behaviour of porcelain cap and pin type insulator polluted with these two different pollutants was investigated. The experiment was carried out by a semi-natural method wherein the insulator was first polluted artificially thereafter natural fog was applied to measure the wet flashover voltage. Test results indicate that the flashover voltages were affected by both soluble salts and non-soluble components deposit on the insulator surface. In case of thick contaminated layer non-soluble deposits greatly reduced the flashover voltage. Moreover, by using regression analysis four empirical models based on different variables have been developed. The empirical models developed in the present work represent a good degree of relation to predicting the flash-over voltage of naturally contaminated insulators.publishedVersio

Optimised performance of cap and pin insulator under wet pollution conditions using a mono-objective genetic algorithm

Extensive research was carried out on the relation between pollution performances of high voltage insulators and their shape. However, very little work has been published using numerical optimisation methods. In this article, we propose an alternative approach for optimising insulators shapes by adopting an optimisation numerical approach, namely the genetic algorithms technique combined with the finite element method for electrical field and leakage current density calculation. The objective is to compare the pollution performance of an industrial cap and pin insulator with its optimised model obtained using a genetic algorithms optimisation method. The impact of the insulator shape and the pollution on the electrical parameters (voltage, electric field and conduction current density distributions) are quantified. In this work, it was shown that the optimised shape performs better than the existing equivalent units when the pollution is deposited near to high voltage terminal located at the pin of a cap-and-pin insulator

Humidity control in different building applications; restaurant and operation theatre

Air conditioning (AC) in tropical climate required dehumidification of air at a low dew point temperature to meet humidity standard. This increase the required cooling energy and heating energy is needed to raise the supply air temperature to meet the room’s design temperature. This research was carried out to study energy efficiency and indoor environment factor in two different applications that is restaurant and operation theatre (OT). A method was proposed to enhance the humidity control and energy efficiency in the AC system by applying psychrometric analysis based on actual measurement. Three (3) different systems were used in this study that consists of economizer damper, desiccant wheel and heat pipe heat exchanger (HPHX).The economizer damper analysed base on fresh air intake requirement for ventilation purposes on standard ASHRAE 55 (2010). Manufacturing software by Novelaire and HPC were used to perform the psychorometric analysis for desiccant wheel and HPHX. At the restaurant, the grand total loads (Qt) of the existing AC system were 296.1 kW as to meet temperature and humidity level requirement. The Qt was reduced to 153.8 kW for economizer damper, 170 kW with heating 60.38 kW for desiccant wheel and 178.3 kW with heating 4.1 kW for HPHX. In actual measurement for the OT, the existing AC system had a grand total load Qt of 90.1 kW with heating 5.6 kW and it did not meet the humidity level requirement. However, the AC system required Qt 95.9 kW with heating 12.2 kW as to meet the humidity level requirement for an OT. By using the HPHX in the system, a reduced Qt of 81.6 kW with heating 17.7 kW was achieved, where as a Qt of 100.8 kW with heating 39.9 kW was attained by utilizing the desiccant wheel, whilst maintaining the humidity level requirement. The economizer damper was not applicable for the OT because the OT requires 100% fresh air intake. As a conclusion, damper economizer was beneficial for energy efficiency in restaurants with reducing of 48% energy used and HPHX was beneficial for energy efficiency with reduced 9.4% in OT compared with existing AC system