A framework for developing a prognostic model using partial discharge data from electrical trees

Insulation breakdown is a key failure mode of high voltage (HV) equipment, with progressive faults such as electrical treeing leading to potentially catastrophic failure. Electrical treeing proceeds from defects in solid insulation, and cables are particularly affected. Research has shown that diagnosis of the fault can be achieved based on partial discharge (PD) analysis. Nonetheless, after diagnosis of a defect, engineers need to know how long they have to take action. This requires prognosis of remaining insulation life. The progression of a defect is far less well understood than diagnosis, making prognosis a key challenge requiring new approaches to defect modelling. The practical deployment of prognostics for cable monitoring is not currently feasible, due to the lack of understanding of degradation mechanisms and limited data relating defect inception to plant failure. However, this thesis advances the academic state of the art, with an eye towards practical deployment in the future. The expected beneficiaries of this work are therefore researchers in the field of HV condition monitoring in general, and electrical treeing within cables in particular. This research work develops a prognostic model of insulation failure due to the electrical treeing phenomenon by utilising the associated PD data from previous experiment. Both phase-resolved and pulse sequence approaches were employed for PD features extraction. The performance of the PD features as prognostic parameters were evaluated using three metrics, monotonicity, prognosability and trendability. The analysis revealed that features from pulse sequence approach are better than phase-resolved approach in terms of monotonicity and prognosability. The key contributions to knowledge of this work are three-fold: the selection of the most appropriate prognostic parameter for PD in electrical trees, through thorough analysis of the behaviour of a number of candidate parameters; a prognostic modelling approach for this parameter based on curve-fitting; and a generalised framework for prognostic modelling using data-driven techniques.Insulation breakdown is a key failure mode of high voltage (HV) equipment, with progressive faults such as electrical treeing leading to potentially catastrophic failure. Electrical treeing proceeds from defects in solid insulation, and cables are particularly affected. Research has shown that diagnosis of the fault can be achieved based on partial discharge (PD) analysis. Nonetheless, after diagnosis of a defect, engineers need to know how long they have to take action. This requires prognosis of remaining insulation life. The progression of a defect is far less well understood than diagnosis, making prognosis a key challenge requiring new approaches to defect modelling. The practical deployment of prognostics for cable monitoring is not currently feasible, due to the lack of understanding of degradation mechanisms and limited data relating defect inception to plant failure. However, this thesis advances the academic state of the art, with an eye towards practical deployment in the future. The expected beneficiaries of this work are therefore researchers in the field of HV condition monitoring in general, and electrical treeing within cables in particular. This research work develops a prognostic model of insulation failure due to the electrical treeing phenomenon by utilising the associated PD data from previous experiment. Both phase-resolved and pulse sequence approaches were employed for PD features extraction. The performance of the PD features as prognostic parameters were evaluated using three metrics, monotonicity, prognosability and trendability. The analysis revealed that features from pulse sequence approach are better than phase-resolved approach in terms of monotonicity and prognosability. The key contributions to knowledge of this work are three-fold: the selection of the most appropriate prognostic parameter for PD in electrical trees, through thorough analysis of the behaviour of a number of candidate parameters; a prognostic modelling approach for this parameter based on curve-fitting; and a generalised framework for prognostic modelling using data-driven techniques

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

Analysis and De-Noising of Partial Discharge Signals in Medium Voltage XLPE Cables

The partial discharge (PD) measurements have been widely used in the field of insulation diagnostics. The presence of partial discharges inside the cable indicates the degradation of insulation material. This thesis deals with the development of insulation diagnostic method based on the partial discharge measurements. The useful information about the partial discharge activity and insulation defects is extracted by the experimental results. A measuring test setup was established in the high voltage laboratory. Artificial cavity was introduced inside the MV XLPE cable by using the traditional needle-plane configuration. The aim of study was to interpret the variations in the partial discharge characteristics over the insulation ageing period in terms of physical phenomenon’s taking place in PD sources. The statistical characteristics formulated with the help of PRPDA technique and ultra-wideband discharge characteristics by using HFCT sensor were studied and analyzed. The variations in these characteristics allow to diagnose the insulation conditions as well as detect the type of discharge mechanisms. In the second part of thesis, detailed analytical study about the de-noising techniques has been conducted. In order to design an efficient de-noising filter for onsite and online PD monitoring system, various factors such as optimal wavelet selection, number of decomposition levels and threshold setting has been studied. An automated self-adaptive de-noising algorithm based on the frequency characteristics of partial discharge signals has been presented in this study

Some Studies on Breakdown of Solid Insulations and it’s Modeling using Soft Computing Techniques

Electrical power systems are experiencing significant changes at the worldwide scale both in size and in complexities. The generating capacities of power plants and application of high voltage has intensively increased due to their inherent advantages, such as, greater efficiency and cost effectiveness. It is, thus essential to know the property of the insulating materials for optimum solution in terms of cost and insulating capability. Out of so many properties of insulation materials, determination of the breakdown voltage continues to evoke a lot of interest to the Electrical Engineers in general and High Voltage Engineers in particular. Hence, it is possible to develop solid insulating materials with excellent breakdown strength and any attempt at modeling the phenomenon with the presence of void would go a long way in assessing the insulation quality. Some of the few important topics reviewed at the beginning of the thesis are the factors affecting the breakdown voltage in general, breakdown voltage study of different composite insulating materials and the factors affecting the breakdown voltage due to Partial Discharges (PD) in voids

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

Partial Discharge Diagnostic Testing of Electrical Insulation Based on Very Low Frequency High Voltage Excitation

Electrical insulation plays an important role in the proper functioning of high voltage power system equipment/components. Examining the condition of insulation is crucial to keep the equipment safe and functioning efficiently. High voltage diagnostic tests, in particular partial discharge measurements, are very effective in detecting early signs of insulation damage. This type of diagnostic test is generally conducted at the power frequency to emulate normal operating condition. However, it is difficult to perform the test on-site due to the large reactive power required when testing high-capacitance objects such as cables. An alternative approach is to conduct the test at very low frequency excitation, commonly at 0.1 Hz, because the required power is proportional to the applied frequency and thus is significantly reduced. However, partial discharge behaviour varies with frequency and thus existing knowledge on interpretations of partial discharge at power frequency cannot be directly applied to test results measured at very low frequency for insulation diagnosis. The motivation of this research is to study partial discharge behaviours at very low frequency and search for physical explanations of such differences. Therefore, this thesis explains those differences in two types of partial discharge, corona discharge and internal discharge, based on extensive experimental measurements and computer simulation. Partial discharge patterns were obtained and analysed using the phase-resolved partial discharge technique. A comprehensive study of corona discharges at different applied voltage waveforms, such as sinusoidal wave and square wave, was carried out under the excitation of very low frequency. Experimental results showed that the inception voltage of corona discharges at very low frequency is dependent on applied voltage waveforms. Furthermore, effects of ambient air on corona discharges were investigated thoroughly at temperatures between 20C and 40C at very low frequency excitation and power frequency for comparison purposes. Measured corona discharge characteristics showed that the increase of ambient temperature results in larger discharge magnitude and causes corona discharges to occur earlier in the phase of the voltage cycle. This research also investigated internal discharge behaviour in a cavity at very low frequency using measurement and simulation. Measurement results showed that partial discharge characteristics are strongly dependent on applied frequency. A dynamic model for numerical computation was developed to study this dependence. The advantage of this model is that it has minimum adjustable parameters to simulate discharges in the cavity. These values were determined using a trial and error approach to fit the simulation results with measured data. Simulation results showed that charge decay has a significant contribution to discharge characteristics at very low frequency. Charge decay causes a reduction of the initial electron generation rate which results in lower discharge magnitude and repetition rate. Also, the statistical time lag of discharge activities was calculated and found exhibiting a great dependence on applied frequency. All in all, the major contribution of this thesis is the development of a dynamic model to characterise physical processes of partial discharge in a cavity. It enables determination of key parameters influencing partial discharge behaviour such as the statistical time lag and the charge decay time constant at different applied frequencies. Moreover, differences in partial discharge characteristics at very low frequency and power frequency as a function of cavity size, voltage waveforms and ambient temperatures are discussed and explained in detail. The findings from this research provide better understanding of discharge behaviours at very low frequency excitation

Multifunctional Hybrid Materials Based on Polymers: Design and Performance

Multifunctional hybrid materials based on polymers have already displayed excellent commitment in addressing and presenting solutions to existing demands in priority areas such as the environment, human health, and energy. These hybrid materials can lead to unique superior multifunction materials with a broad range of envisaged applications. However, their design, performance, and practical applications are still challenging. Thus, it is highly advantageous to provide a breakthrough in state-of-the-art manufacturing and scale-up technology to design and synthesize advanced multifunctional hybrid materials based on polymers with improved performance.The main objective of this interdisciplinary book is to bring together, at an international level, high-quality elegant collection of reviews and original research articles dealing with polymeric hybrid materials within different areas such as the following:- Biomaterials chemistry, physics, engineering, and processing;- Polymer chemistry, physics and engineering;- Organic chemistry;- Composites science;- Colloidal chemistry and physics;- Porous nanomaterials science;- Energy storage; and- Automotive and aerospace manufacturing

Shortest Route at Dynamic Location with Node Combination-Dijkstra Algorithm

Abstract— Online transportation has become a basic requirement of the general public in support of all activities to go to work, school or vacation to the sights. Public transportation services compete to provide the best service so that consumers feel comfortable using the services offered, so that all activities are noticed, one of them is the search for the shortest route in picking the buyer or delivering to the destination. Node Combination method can minimize memory usage and this methode is more optimal when compared to A* and Ant Colony in the shortest route search like Dijkstra algorithm, but can’t store the history node that has been passed. Therefore, using node combination algorithm is very good in searching the shortest distance is not the shortest route. This paper is structured to modify the node combination algorithm to solve the problem of finding the shortest route at the dynamic location obtained from the transport fleet by displaying the nodes that have the shortest distance and will be implemented in the geographic information system in the form of map to facilitate the use of the system. Keywords— Shortest Path, Algorithm Dijkstra, Node Combination, Dynamic Location (key words