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S. Abdul Madhar
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This paper presents the investigation on surface discharge behavior of various dielectric samples under DC. It sequentially develops the knowledge base for the study and analysis of the partial discharge (PD) defect with the goal of PD defect identification under DC. In order to facilitate this, the material properties of the dielectric are measured. Finite Element (FEM) simulation is used to obtain the preliminary estimates of the electric field and dielectric properties that concern partial discharge behavior. The DC-PD tests performed on the surface dielectric samples demonstrate a highly plausible behavior based on simulation results and other literature. It also displays a great degree of similarity towards the AC surface discharge behavior. The paper concludes by presenting novel partial discharge fingerprints for the surface PD defect that will aid in defect identification under HVDC.
...
This paper presents the investigation on surface discharge behavior of various dielectric samples under DC. It sequentially develops the knowledge base for the study and analysis of the partial discharge (PD) defect with the goal of PD defect identification under DC. In order to facilitate this, the material properties of the dielectric are measured. Finite Element (FEM) simulation is used to obtain the preliminary estimates of the electric field and dielectric properties that concern partial discharge behavior. The DC-PD tests performed on the surface dielectric samples demonstrate a highly plausible behavior based on simulation results and other literature. It also displays a great degree of similarity towards the AC surface discharge behavior. The paper concludes by presenting novel partial discharge fingerprints for the surface PD defect that will aid in defect identification under HVDC.
Defect Identification through Partial Discharge Analysis on HVDC
Partial Discharge Fingerprinting
The electricity grid spanning hundreds of thousands of kms is one of the most complex man-made network built in human history. Today, after a century of growth, progress and innovation, the electricity grid is in the process of undergoing another landmark shift in its operation. The introduction of renewable energy sources, especially, offshore wind connected to the load centres through >80 kms of underground subsea cable has caused a shift from AC transmission towards DC transmission. This is because AC cables suffer from high charging currents that reduce the useful current carrying capacity for long cables. On the contrary, High Voltage DC (HVDC) is acclaimed with higher current capacity for the same conductor dimension as AC and as a result the more sustainable alternative. Therefore, the infrastructure developed around the AC grid is now under pressure to adapt itself to the DC technology. This implies a dramatic change in a cascade of procedures and processes, beginning from designing new DC components, its testing and qualification, its validation and up to its commissioning, control and operation. Every step in the process is expected to be crucial and challenging given the newness of the technology and lack of experience.In the current scenario, this research rests itself in the testing and qualification phase of these DC components. The field of HV testing has not been exclusive tothis pressure to adapt and improvise its processes to accommodate the newest DC technological trends. New requirements are being defined to determine the quality of HVDC components and new methodologies developed to fulfil this. One of the most widespread test methodologies that has come to become a part of several tests such as factory acceptance tests (FATs), site acceptance test (SATs), routine tests and type tests is the measurement of Partial Discharge (PD). Partial discharge is a dielectric phenomenon that when measured is used as a proven marker for insulation quality. The inherent differences in the performance of the insulation under AC and DC operation have not allowed a direct adaption of the PD analysis techniques from AC to DC. This research will investigate the possibilities of defect identification through PD measurements under DC.With increasing HVDC installations such as GIS/GIL, cable links, convertors etc.,the method for its design validation and fitness through partial discharge measurement is gaining increasing popularity. This is only expected to rise with the introduction of renewable energy, electric vehicles (EVs) and its related infrastructure, lowered dependency on fossil fuels and an international policy shift towards the reduction of greenhouse gases. Moreover, given the remarkable success of partial discharge measurements in defect identification under AC, mounting expectations for a similar prospect under DC conditions is a thriving notion. Therefore, as a first steps towards characterizing PD defects under DC conditions this thesis studies the physics of discharge progression of 3 common defect types namely, corona, floating electrode and surface discharge in detail, in order to recognize minor if not major differences that will enable defect recognition. With this investigation, a comprehensive procedure is devised, enabling the identification of the three defects that were studied under DC conditions. The research also proposes the novel WePSA (Weighted Pulse Sequence Analysis) patterns discussed in chapter 7, section 7.2.2 as a prospective defect fingerprint that will allow identification of defects under DC.The simplicity and robust nature of these patterns make them self-explanatoryand easy to interpret. Several other unique defect behavioural features discovered during the study add value to this research and bring it closer to accomplishing the final goal of PD defect identification under DC stress conditions. This research could serve as a starting point for the scientific community to investigate further the other defect models and extend the defect discrimination strategy proposed in this thesis, chapter 7, section 7.5.
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The electricity grid spanning hundreds of thousands of kms is one of the most complex man-made network built in human history. Today, after a century of growth, progress and innovation, the electricity grid is in the process of undergoing another landmark shift in its operation. The introduction of renewable energy sources, especially, offshore wind connected to the load centres through >80 kms of underground subsea cable has caused a shift from AC transmission towards DC transmission. This is because AC cables suffer from high charging currents that reduce the useful current carrying capacity for long cables. On the contrary, High Voltage DC (HVDC) is acclaimed with higher current capacity for the same conductor dimension as AC and as a result the more sustainable alternative. Therefore, the infrastructure developed around the AC grid is now under pressure to adapt itself to the DC technology. This implies a dramatic change in a cascade of procedures and processes, beginning from designing new DC components, its testing and qualification, its validation and up to its commissioning, control and operation. Every step in the process is expected to be crucial and challenging given the newness of the technology and lack of experience.In the current scenario, this research rests itself in the testing and qualification phase of these DC components. The field of HV testing has not been exclusive tothis pressure to adapt and improvise its processes to accommodate the newest DC technological trends. New requirements are being defined to determine the quality of HVDC components and new methodologies developed to fulfil this. One of the most widespread test methodologies that has come to become a part of several tests such as factory acceptance tests (FATs), site acceptance test (SATs), routine tests and type tests is the measurement of Partial Discharge (PD). Partial discharge is a dielectric phenomenon that when measured is used as a proven marker for insulation quality. The inherent differences in the performance of the insulation under AC and DC operation have not allowed a direct adaption of the PD analysis techniques from AC to DC. This research will investigate the possibilities of defect identification through PD measurements under DC.With increasing HVDC installations such as GIS/GIL, cable links, convertors etc.,the method for its design validation and fitness through partial discharge measurement is gaining increasing popularity. This is only expected to rise with the introduction of renewable energy, electric vehicles (EVs) and its related infrastructure, lowered dependency on fossil fuels and an international policy shift towards the reduction of greenhouse gases. Moreover, given the remarkable success of partial discharge measurements in defect identification under AC, mounting expectations for a similar prospect under DC conditions is a thriving notion. Therefore, as a first steps towards characterizing PD defects under DC conditions this thesis studies the physics of discharge progression of 3 common defect types namely, corona, floating electrode and surface discharge in detail, in order to recognize minor if not major differences that will enable defect recognition. With this investigation, a comprehensive procedure is devised, enabling the identification of the three defects that were studied under DC conditions. The research also proposes the novel WePSA (Weighted Pulse Sequence Analysis) patterns discussed in chapter 7, section 7.2.2 as a prospective defect fingerprint that will allow identification of defects under DC.The simplicity and robust nature of these patterns make them self-explanatoryand easy to interpret. Several other unique defect behavioural features discovered during the study add value to this research and bring it closer to accomplishing the final goal of PD defect identification under DC stress conditions. This research could serve as a starting point for the scientific community to investigate further the other defect models and extend the defect discrimination strategy proposed in this thesis, chapter 7, section 7.5.
The discharge over dielectric interfaces popularly known as surface discharge is a very common defect type that is associated with its respective discharge pattern under AC voltages. However, the same designs behave differently under DC voltages leading up to erratic PD behavior. To understand the process of surface discharge an equivalent circuit model is developed, and its influencing material parameters such as the volumetric and surface electrical conductivities and the relative permittivity are measured experimentally. This paper describes the methodology and setup of the measurement based on international standards. The final goal is to provide the constituent model parameters that can describe the surface discharge model under DC stress.
...
The discharge over dielectric interfaces popularly known as surface discharge is a very common defect type that is associated with its respective discharge pattern under AC voltages. However, the same designs behave differently under DC voltages leading up to erratic PD behavior. To understand the process of surface discharge an equivalent circuit model is developed, and its influencing material parameters such as the volumetric and surface electrical conductivities and the relative permittivity are measured experimentally. This paper describes the methodology and setup of the measurement based on international standards. The final goal is to provide the constituent model parameters that can describe the surface discharge model under DC stress.
This paper presents several approaches to the analysis of partial discharge (PD) data. Three common defects namely corona, surface and floating electrode are studied with the goal of defect identification under DC stress conditions. One of the major concerns with DC-PD testing, is its non-repetitive/erratic pulse pattern. This paper, however, only deals with the repetitive stages of discharge that will allow the study of their resultant patterns and trends. Several unique features such as the formative trend in the probability plot of time between discharges for the three common defect types shows promise in the quest for defect identification under DC. Further, the paper also describes in which way a three-pulse PSA diagram cannot serve as a standalone figure and hence requires a change in perspective by either adding or reducing a dimension. The last part of the paper presents a test methodology to identify the discharge source based on various discharge features.
...
This paper presents several approaches to the analysis of partial discharge (PD) data. Three common defects namely corona, surface and floating electrode are studied with the goal of defect identification under DC stress conditions. One of the major concerns with DC-PD testing, is its non-repetitive/erratic pulse pattern. This paper, however, only deals with the repetitive stages of discharge that will allow the study of their resultant patterns and trends. Several unique features such as the formative trend in the probability plot of time between discharges for the three common defect types shows promise in the quest for defect identification under DC. Further, the paper also describes in which way a three-pulse PSA diagram cannot serve as a standalone figure and hence requires a change in perspective by either adding or reducing a dimension. The last part of the paper presents a test methodology to identify the discharge source based on various discharge features.
Corona is one of the most common forms of partial discharge (PD) occurring in high voltage (HV) energy systems. The corona mechanism in air is not exclusive to the field of energy applications but has also been widely studied by physicists to theorize mechanisms of charge transfer during the different phases of gas discharge. The phases of the discharge and its corresponding behavior with alternating voltage (AC) are well established and represented through various discharge trends, patterns and stages. This not only makes the identification of the PD defect possible but also helps evaluate the risk. This paper investigates corona configurations under DC stress in an attempt to create a similar outline of the defect as exists under AC. The defect is studied in terms of the pulse sequence information. The measurement system requirements are kept within a realistic realm to preserve applicability to industrial measurements. Finally, it makes selective recommendations for the effective identification of the discharge condition under DC stress.
...
Corona is one of the most common forms of partial discharge (PD) occurring in high voltage (HV) energy systems. The corona mechanism in air is not exclusive to the field of energy applications but has also been widely studied by physicists to theorize mechanisms of charge transfer during the different phases of gas discharge. The phases of the discharge and its corresponding behavior with alternating voltage (AC) are well established and represented through various discharge trends, patterns and stages. This not only makes the identification of the PD defect possible but also helps evaluate the risk. This paper investigates corona configurations under DC stress in an attempt to create a similar outline of the defect as exists under AC. The defect is studied in terms of the pulse sequence information. The measurement system requirements are kept within a realistic realm to preserve applicability to industrial measurements. Finally, it makes selective recommendations for the effective identification of the discharge condition under DC stress.
Partial discharge is a prevalent phenomenon under high voltage (HV) where the discharge partially bridges the gap between two electrodes. At increasing voltage levels, physical dimensions and distances between the electrical parts become critical. Designing electrical components for such high voltages and planning of high voltage laboratories/tests need to deliberate this aspect as it could lead to possible complications such as partial discharges (PD) from the floating metal components. Floating electrodes under AC voltages are associated with a distinctive PRPD pattern. However, there is a lack of literature on the physical interpretation of this pattern. Likewise, under DC voltages, no consistent explanation towards the defect behavior has been reported. Therefore, this paper presents an in-depth study of the floating electrode defect configuration under AC and DC voltages. Subsequently, it provides the physical interpretation of the discharge patterns obtained through the stepwise description of the discharge stages under both conditions. By formulating criteria for repetitive discharges and presenting novel PD fingerprints for DC floating electrode configuration, the outcomes published in this paper contribute towards prospective PD defect identification tools under HVDC.
...
Partial discharge is a prevalent phenomenon under high voltage (HV) where the discharge partially bridges the gap between two electrodes. At increasing voltage levels, physical dimensions and distances between the electrical parts become critical. Designing electrical components for such high voltages and planning of high voltage laboratories/tests need to deliberate this aspect as it could lead to possible complications such as partial discharges (PD) from the floating metal components. Floating electrodes under AC voltages are associated with a distinctive PRPD pattern. However, there is a lack of literature on the physical interpretation of this pattern. Likewise, under DC voltages, no consistent explanation towards the defect behavior has been reported. Therefore, this paper presents an in-depth study of the floating electrode defect configuration under AC and DC voltages. Subsequently, it provides the physical interpretation of the discharge patterns obtained through the stepwise description of the discharge stages under both conditions. By formulating criteria for repetitive discharges and presenting novel PD fingerprints for DC floating electrode configuration, the outcomes published in this paper contribute towards prospective PD defect identification tools under HVDC.
Partial discharge measurements performed according to IEC 60270 has become an essential tool for the quality assurance of HV equipment. The main goal of IEC 60270 is to standardize and unify PD measurements to get comparable results for tests performed at various locations, using different equipment and by different operators. This paper aims at providing clear and unambiguous guidelines on how to perform repeatable and comparable PD measurements in compliance with one of the most popular international testing standards in Europe, the IEC 60270. This paper also discusses the functionality of the various components in the measuring setup. In addition, it makes some invaluable recommendations based on scientific knowledge regarding the selection of proper PD test and evaluation parameters to ensure correctness of obtained test results. The main focus is on the selection of a suitable frequency measurement range, which is a key step in the quasi-integration process involved in the charge estimation of the PD pulse.
...
Partial discharge measurements performed according to IEC 60270 has become an essential tool for the quality assurance of HV equipment. The main goal of IEC 60270 is to standardize and unify PD measurements to get comparable results for tests performed at various locations, using different equipment and by different operators. This paper aims at providing clear and unambiguous guidelines on how to perform repeatable and comparable PD measurements in compliance with one of the most popular international testing standards in Europe, the IEC 60270. This paper also discusses the functionality of the various components in the measuring setup. In addition, it makes some invaluable recommendations based on scientific knowledge regarding the selection of proper PD test and evaluation parameters to ensure correctness of obtained test results. The main focus is on the selection of a suitable frequency measurement range, which is a key step in the quasi-integration process involved in the charge estimation of the PD pulse.
Partial Discharges (PD) have long been studied under AC field stress and are widely accepted as a good indicator of component health. However, the advent of HVDC brought new challenges, as the pre-existing knowledge in the area of PD is not applicable to DC. The discharge behavior has been found to be erratic and there is no plausible evidence yet, that correlates discharges with insulation deterioration. The inability to produce stable behavioral patterns in DC-PD has also led to a spark in interest in the application of several non-conventional measuring methods, e.g. the measurement using UHF sensors. Therefore, this paper deals with the measurement of time synchronized PD measurements through conventional electrical and UHF methods for a novel comparison of DC discharge patterns generated by a needle-plate electrode arrangement in air. The different configurations of the defect are studied under both voltage polarities and the observations are discussed in terms of pulse magnitude and repetition rate. In addition, this paper exploits the opportunities of computational power for post-processing to obtain Pulse Sequence Analysis (PSA) diagrams of the discharge data.
...
Partial Discharges (PD) have long been studied under AC field stress and are widely accepted as a good indicator of component health. However, the advent of HVDC brought new challenges, as the pre-existing knowledge in the area of PD is not applicable to DC. The discharge behavior has been found to be erratic and there is no plausible evidence yet, that correlates discharges with insulation deterioration. The inability to produce stable behavioral patterns in DC-PD has also led to a spark in interest in the application of several non-conventional measuring methods, e.g. the measurement using UHF sensors. Therefore, this paper deals with the measurement of time synchronized PD measurements through conventional electrical and UHF methods for a novel comparison of DC discharge patterns generated by a needle-plate electrode arrangement in air. The different configurations of the defect are studied under both voltage polarities and the observations are discussed in terms of pulse magnitude and repetition rate. In addition, this paper exploits the opportunities of computational power for post-processing to obtain Pulse Sequence Analysis (PSA) diagrams of the discharge data.
Conference paper
(2019)
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Saliha Abdul Madhar, Petr Mraz, Sonia Raquel Barrios Pereira, Nabil Akroud
Asset condition monitoring through Partial Discharge (PD) measurements is widely used for pre-emptive maintenance especially in cable networks. Several monitoring systems rely on measurements in the High Frequency (HF) band using wideband sensors when it comes to PD monitoring to have higher Signal to Noise Ratios (SNR), ignoring the radical attenuation of the higher frequencies by the cable. This paper presents measured values of attenuation from measuring loops and several other important insights that can help in the interpretation of PD measured data.
...
Asset condition monitoring through Partial Discharge (PD) measurements is widely used for pre-emptive maintenance especially in cable networks. Several monitoring systems rely on measurements in the High Frequency (HF) band using wideband sensors when it comes to PD monitoring to have higher Signal to Noise Ratios (SNR), ignoring the radical attenuation of the higher frequencies by the cable. This paper presents measured values of attenuation from measuring loops and several other important insights that can help in the interpretation of PD measured data.
In this contribution, the partial discharge behavior of two types of floating electrodes under DC stress in air at atmospheric pressure are investigated. Either a hexagonal-shaped nut or a sphere are positioned at a distance of 0.4 mm to the high voltage electrode. The influence of the geometry of the floating electrodes as well as the level and polarity of the applied DC voltage on the partial discharge activity are investigated. Several PD measurement techniques are used simultaneously, namely electrical measurement, ultra-high frequency (UHF) and both high frequency current transformer (HFCT) and shunt measurements. The obtained data is post-processed and visualized with Pulse Sequence Analysis (PSA) diagrams in order to provide characteristic patterns of the investigated defect. In addition, a corona camera detecting the light emissions generated by the discharges provide a further understanding of the defect mechanisms.
...
In this contribution, the partial discharge behavior of two types of floating electrodes under DC stress in air at atmospheric pressure are investigated. Either a hexagonal-shaped nut or a sphere are positioned at a distance of 0.4 mm to the high voltage electrode. The influence of the geometry of the floating electrodes as well as the level and polarity of the applied DC voltage on the partial discharge activity are investigated. Several PD measurement techniques are used simultaneously, namely electrical measurement, ultra-high frequency (UHF) and both high frequency current transformer (HFCT) and shunt measurements. The obtained data is post-processed and visualized with Pulse Sequence Analysis (PSA) diagrams in order to provide characteristic patterns of the investigated defect. In addition, a corona camera detecting the light emissions generated by the discharges provide a further understanding of the defect mechanisms.