The leakage current components as a diagnostic tool to estimate contamination level on high voltage insulators

The current paper presents an alternative and innovative technique to predict the severity of pollution of high voltage insulator using a higher harmonics component with up to the 7th component of leakage current. The leakage current was measured using a current transformer and a shunt resistor. Next, laboratory tests were conducted on glass and porcelain insulators with artificial pollution under salt-fog pollution state which is further represented by three levels, namely light, medium, and high contamination. In this case, the formulation of a new severity of harmonic index refers to a ratio of the sum of 5th and 7th to the 3rd harmonic component. More importantly, the new index managed to provide more accurate results when used as a diagnostic tool for the levels of pollution, compared to the ratio of the total harmonic distortion (THD) to the number of odd harmonics components (n) as the boundaries. In this case, the insulators were found to be in a clean and normal condition when the K(5+7)/3 value was greater than 3%. Contrastingly, the insulators were in an extreme condition when the K(5+7)/3 was lower than 3%. Nevertheless, there is a high probability of a flashover in glass and porcelain insulators if the K(5+7)/3 value is less than 2%. The present study shows the possibility of utilizing the value of strange harmonics up to the 7th component of leakage current as the parameter for the monitoring of leakage current in overhead insulators in the presence of contamination. Overall, it can be concluded that the 3rd, 5th, and 7th harmonics details extracted from the leakage current act as a good indicator for the level of contamination

The performance of high voltage; outdoor insulation in polluted environments

"An iron wire, 12000 feet in length, was suspended about five feet from the ground by silk cords; one end of it was connected to the globe of an electrical machine, and at the other a lead ball was hung in order to perceive when the matter reached it. After five or six turns of the wheel, the matter had passed along the whole wire and communicated its virtue to the ball, which instantly attracted and repelled light bodies. 2. As this ball was equally electrified with every part of the wire, it is probable that the electric matter would instantly pervade a wire of a still greater length, provided we had a proper apparatus for the purpose. 3. Several metals and other conductors were substituted in place of the ball, and all received the electricity in the same manner. The ball and touched with other non-conductors, :when' the finger, gave a luminous spark and as smart a shock as when the end of the wire next to 'the 'gTobe·vas touched. All these effects instantly ceased whenever .. any person not electrified touched any part of the wire and commenced again a few seconds after his hand was withdrawn. The same effects are produced, though with more difficultly, when hair or woollen ropes were substituted in place of the silk ones: But they were entirely stopped by hemp ropes or when the silk ones were wetted.

Condition Monitoring of Outdoor High Voltage Insulators, Online and Offline Techniques: A review

Outdoor insulator plays a vital role in high voltage transmission and distribution system. The performance and properties of outdoor insulator may severely affect due to various types of pollutants. The failure of insulation in high voltage system results in loss of supply and a huge loss of electrical energy to distribution utilities. In order to reduce power losses and provide a reliable power transmission, selection and design of insulators is very important. To monitor the condition and performance of outdoor insulator in contaminated conditions an appropriate diagnostic technique is required. In this paper various online and offline techniques for conditioning monitoring of outdoor insulators are reviewed under different contaminated conditions. To maintain the healthy environment, the condition monitoring of power line insulators is an important requirement. There are number of techniques that have been introduced to fulfil this requirement. Each technique used at different contaminated condition have their own pros and cons. The findings indicate that the most important effect on the surface of the insulators based on the contamination on the surface leakage current and the flashover voltage. This paper will help in the selection and design of condition monitoring techniques for high voltage outdoor insulator

Developing a smart monitoring system for leakage currents from insulators on wooden poles

In Australia and many other countries, power distribution lines are carried on wooden poles. These lines suspended on insulators, which are fixed to wooden poles, pass cities as well as bushlands. Under different weather conditions, insulators become contaminated, and in particular, with damp weather, these insulators lose their ability to provide a perfect insulation between the high voltage conductor and the ground (through high impedance objects such as wood). A leakage current, small in magnitude, starts flowing from the high voltage conductor to the ground across the polluted insulator and through the wooden pole. If this phenomenon continues over some time, the currents start heating the wood where there is an abundance of wood-to-metal contact. At a certain stage, it will start smoking and this may lead to a pole fire. The obvious consequences of this are the loss of power to customers, public safety hazards and potential disasters such as bushfires. This thesis aims at determining which measure or combination of measures of leakage current are best suited for creating a ‘Leakage Current Health Index’ (LCHI) that can be later used to provide a power system operator with health status for a feeder or system, indicating how urgent a response is needed. To achieve this goal, the impedance characteristics of wooden poles altering the leakage current from insulators are investigated to better understand the role of wood in leakage current signatures. The effective impedance of wood used for poles in Victoria, Australia is established for the first time. Examining the impedance properties of typical Copper Chromium Arsenate (CCA) impregnated wood for 66 kV distribution poles shows dangerous conductance properties of wood at this voltage, providing an explanation for these poles catching fire at triple the rate of 22 kV distribution poles. After a systematic investigation of wood used for poles, a typical impedance characteristic is established for a weathered CCA impregnated wooden pole operating at 22 kV under both dry and wet weather conditions. Next, the leakage current from a single high voltage insulator is examined for various contamination levels and under different weather conditions. A new nonlinearity measure is established which utilises the Pearson correlation coefficient to measure the degree of leakage current nonlinearity and to build leakage current profiles of a single insulator under different conditions prior to flashover. Several fractal dimensions are also considered for the first time to measure characteristics of the leakage current profile of a single insulator. These measures are able to quantitatively differentiate between various levels of insulator contamination and different weather conditions, showing an enhanced level of nonlinear activity in the stage prior to insulator flashover. After developing an understanding of a single insulator, systematic modelling is used to build measure profiles of leakage currents for a simple power line, a lossless power line and a lossy power line. Finally, power utility zone substation data for a pole top fire are examined to verify the validity of the profiles observed utilising the measuring techniques determined suitable for establishing a LCHI

Effect of some of climatic conditions in the performance of outdoor HV silicone rubber insulators

Silicone rubber (SiR) insulators are increasingly being used mainly because of their superior performance under wet polluted conditions compared to conventional porcelain and glass. However, in polluted environments with high moisture levels, electrical discharges will develop on the insulator surfaces. In the long term, electrical discharges cause degradation of SiR insulator in the form of tracking and erosion due to dry-band arcing that takes place when leakage current (LC) develops, and both are detrimental to the life of the insulation. This thesis presents an experimental study on the electric performance of aged high voltage outdoor silicone rubber insulators. In addition to the literature reviewed of the performance of silicone rubber insulators subjected to different climatic conditions, which is resulting in loss of their unique property named ‘hydrophobicity’, the research is concentrated in three areas: (i) Study of the effect of ultraviolet (UV) irradiation on the performance of silicone rubber insulation systems: 11kV non-textured and 4mm Textured Shank insulators (TS4) (TS4 is a new insulator design using intersection of 4mm square texture pattern on the shank regions of the insulator) were prepared in vacuum casting machine. Irradiated insulators were tested under different conditions. Dry-band formation and electrical discharges on their surfaces are dependent on the UV doses. Degradation of SiR insulators in a form of tracking and erosion is result in loss the surface hydrophobicity by UV irradiation, and decrease of the expected life of the insulators. Silicone rubber insulator electric performance was found to be affected by the experimental conditions. LC on relatively hydrophobic surfaces was found to exist and increase on overall insulators with increasing the exposure doses of UV irradiation, by increase the number of applied UV cycles. (ii) Development a new test set-up to determine the effectiveness of orientation angle on the performance of silicone rubber insulators subjected to different wet and pollution conditions: LC of silicone rubber insulators were increased with changes in the orientation angle from vertical to horizontal, where the TS4 showed its superior performance under fog conditions in the vertical orientation. (iii) A new test procedure, based on the high voltage ramp test method and standard wet test method, named ‘high voltage rain ramp test’, is proposed to evaluate the flashover performance of the TS4 silicone rubber insulators under simulated rain conditions at different orientations. Its flashover performance was compared with non-textured insulators. TS4 silicone rubber insulators are less suitable for wet weather conditions in any orientation, due to the following reasons: (a) in vertical orientation a very low flashover voltage was observed due to the development of high magnitude electric fields in the insulator shank region, and (b) for the inclined and horizontal orientations, non-textured insulators exhibit a better flashover performance than their textured equivalents. Hence, less improvement is achieved, due to use an expensive and intricate insulator design

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

Coatings for outdoor high voltage insulators

As the range of transmission voltage increases, the pollution severity of the site becomes the most important factor in determining the insulation level of the system. Flashover on polluted insulators poses a serious threat to the reliability of the system and leads to system outages. There are many remedial measures to minimize the flashover of a porcelain insulator under pollution conditions. One such method is the application of hydrophobic coatings such as Room Temperature Vulcanizing Silicone Rubber (RTV- SiR) and Grease coatings on the surface of ceramic insulators. A recently proposed solution for contaminated outdoor insulators consists of the application of the Nanocoating “Voltshield” onto the surface of the insulator. This thesis reports a comparative assessment of the performance of these coating systems. Laboratory testing of coated porcelain insulators has been undertaken based on the solid layer method of IEC 60507 (artificial pollution- clean fog testing) and IEC 60587 (the inclined plane tests and constant voltage-liquid contaminants) to evaluate the coatings’ resistance against tracking and erosion. The performance of these coatings was assessed by monitoring the leakage current on the insulator surfaces. The applied voltage and the leakage current signals were acquired throughout the tests and saved for further analysis. The effect of UV radiation on the coatings has also been investigated. In addition, hydrophobicity tests were performed on the coated insulators. It was found that the Nanocoating reduces the leakage current by 90% whilst the energy absorbed on the insulator surface is reduced by 98% when compared to an uncoated insulator. The Nanocoating showed good resilience to sand blasting, but under long exposure to sand blasting, the surface began to degrade and showed pockmarks. The Nanocoated insulator showed good stability under UV exposure in terms of leakage current suppression. However, Nanocoated insulator lost its hydrophobicity on exposure to fog, and has lower flashover voltage than the uncoated insulator by 12.5%. Similar observations were made for the RTV coatings, where the current magnitude reduced by 92%, the energy absorbed on the insulator surface is reduced by 99% when compared to uncoated insulator and the flashover voltage is increased by 50%. RTV coating materials showed good resistance against tracking and erosion even after UV exposure. The electric field and voltage distribution along the leakage surface of coated and uncoated ceramic insulators under clean and polluted conditions were studied using finite element analysis COMSOL Multiphysics®. The electric field peaked at both the HV electrode and the ground electrode, and the presence of pollution in the form of water droplets on the coated insulator increased the electric field at the HV electrode. This study shows that the application of protective coatings to HV outdoor insulators significantly improves their performance. A reduction in surface current and power dissipation is observed, and a reduction in surface heating results in less dry-band arcing. A reduction in dissipated energy can make a contribution to reducing the total loss on the power system. In addition it showed the ability of coatings to resist tracking and erosion which leads to longer coating life under severe weather conditions. The coatings also increased the flashover voltage of the insulators which leads to more stable power system