A Review and Functional Analysis of Space Charge Measurement Deconvolution Techniques for HVDC Cables

Cross linked polyethylene (XLPE) is used in an electric power cable as insulation materials. The maximum thickness of XLPE layer is 27mm in a 500kV class electric power cable. The pulsed electro acoustic (PEA) method is widely used to measure space charge distribution in dielectric materials. When measuring the space charge distribution in dielectric materials by using the normal PEA method, the acoustic wave (PEA signal) obtains the space charge profile detected by the piezoelectric device in the system. Usually the sample thickness is less than 10mm in normal PEA method. When a thicker sample is used as a sample, the space charge measurement is very difficult in the PEA method, because the acoustic wave from the upper electrode strongly decreases with the thickness in comparison with the acoustic wave from lower electrode. By using the remade PEA system, the space charge distributions have been measured in 27mm thick XLPE samples under about 1kV/mm DC electric field. The experimental results show that the remade PEA system can detect the PEA signal form the lower and upper electrodes in samples. The deconvolution technique on the dispersion in the thick sample is also remade.

We investigated the relationship between the space charge accumulation characteristics and the breakdown in various combination of multilayered polyimide samples under dc stress using the pulsed electro acoustic (PEA) method. In recent years, there are many examples which a multilayered polyimide film is used as the flexible Printed-Circuit Board (PCB) inside an advanced electronic devices or motor windings. Therefore, it is necessary to investigate the insulation performance of the multilayered polyimide. In previous work, it has been revealed that a space charge accumulated in polyimide film under a high stress and it is closely related to the electrical breakdown. Therefore, it is also necessary to investigate the space charge accumulation characteristics of the multilayered type sample. In this paper, we measured the space charge accumulation in various combinations of the multilayered samples under dc high electric field at 80°C by using the PEA method. From the space charge measurement, we found that the multilayered sample has more superior insulating properties than the single layer sample. Furthermore, we found that it is hard to have the breakdown by arranging a thin layer putting next to the anode electrode.

Voltage source converters (VSCs) have emerged as the key components in modern power systems, facilitating efficient energy conversion and flexible power flow control. Understanding the fundamental circuit model of VSCs is essential for their accurate modeling and analysis in power system studies. A basic voltage source converter circuit model connected to an LC filter is essential because it lowers the harmonic distortions and enhances the overall power quality of the micro-grid. This guarantees a clean and steady power supply, which is necessary for the integration of multiple renewable energy sources and sensitive loads. A comprehensive methodology for developing a basic circuit model of VSCs, focusing on the key components and principals involved, is presented in this paper. The methodology includes the modeling of space vector pulse-width modulation (SVPWM) as well as the direct quadrature zero synchronous reference frame. Different design controls, including the design of current control loop in the S-domain, the design of the direct current (DC) bus voltage control loop in the S-domain, and the design of the alternating current (AC) voltage control loop in the S-domain, are explored to capture the dynamic behavior and control strategies of VSCs accurately. The proposed methodology provides a systematic framework for modeling VSCs, enabling engineers and researchers to analyze their performance and assess their impact on power system stability and operation. Future studies can be conducted by using case studies and simulation scenarios to show the efficiency and applicability of the developed models in analyzing VSC-based power electronics applications, including high-voltage direct current (HVDC) transmission systems and flexible alternating current transmission systems (FACTS). The significance of this work lies in its potential to advance the understanding and application of VSCs, contributing to more resilient and efficient power systems. By providing a solid foundation for future research and development, this study supports the ongoing integration of renewable energy sources and the advancement of modern electrical infrastructure.

The treeing phenomena are well known as an initiation process of electrical breakdown in the electric power cables. It is discussed that the charge injection from electrode is related to the growth of the tree. The space charge measurement technique by the pulsed electro acoustic (PEA) method is widely used. However, the measurement in the non-uniform electric field has not been realized in PEA method. The space charge distribution signal (PEA signal) in a needle-plate and line-plate electrode system in a silicone rubber specimen have been measured. Although the PEA signal from the needle electrode cannot be detected, the PEA signal from the line electrode can be detected. The PEA signals were measured under various dc field in Silicone rubber. In this paper, some transient state space charge signals in the line-plate electrode system in PEA method have been reported.

The presence of space charges within the oil and pressboard of converter transformers could distort the original Laplacian field. This could lead to the local electric field enhancement and accelerate the degradation of the insulation materials, which could ultimately result in electrical breakdown. Therefore, space charge measurement is the significant tool to evaluate the insulation properties of dielectric materials. Several factors could affect the space charge behaviour including temperature, moisture, ageing and electric field. Considering the joule heating and stray losses, this paper mainly focuses on the temperature gradient effect on space charge behaviour of multilayers pressboard/oil/pressboard. Space charge behaviour is measured using the modified pulsed electroacoustic (PEA) technique. The space charge recovery methodology is proposed in this paper for three layers pressboard/oil/pressboard. It has been found that the maximum electric field position is opposite depending on the temperature of the anode. The maximum electric field occurs at the pressboard near the anode under the ambient temperature while that is near the cathode under the temperature gradient.

The generation, accumulation, migration and dissipation of the space charge may influence the properties of dielectric largely. In order to study the effect of particle diameters and contents on space charge in epoxy resin composites, micro- and nano- Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /epoxy resin composites were prepared in laboratory by adding Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles into epoxy matrix material. The space charge measurement was performed on both kinds of samples and neat epoxy resin based on pulsed electro-acoustic (PEA) method before and after AC aging. It was found that before AC aging, more space charge was accumulated in micro-composites and nano-composites compared with neat epoxy resin when under 3 kV/mm and 10 kV/mm. And the amount of space charge in Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /epoxy resin composites increased with the increasing of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> content. After the AC aging, it was found that the aging resistance of nano-composites was stronger than that of neat epoxy and micro-composites.

With the increasing use of HVDC and MVDC assets, the fundamental topic of space charge measurements in full-size cables has to be faced properly. Space charge can be a significant threat to DC insulation system reliability. In this paper, the development of an innovative Pulsed Electro-Acoustic (PEA) device to measure the space charge distribution of HVDC and MVDC cables is presented. Issues related to the real cable structure, thickness, (and thus signal attenuation), and noise are dealt with. Specifically, the effect of different types of electrodes, thickness, and materials on PEA signal measurement accuracy is discussed. It is shown that measurement results can be still effective and accurate in a simpler and smaller structure than those used at present for flat specimens or model cables. In order to mitigate the influence of environmental noise and multiple reflection waves, a new adaptive algorithm based on wavelet analysis is proposed. By combining time-frequency analysis with the adaptive filtering method, space charge signals can be extracted from noise in a lossless way. The study also shows that the new algorithm has better performance and stability as regards attenuation and dispersion factors. The validity of the improved recovery technique is proved by testing on polymeric cable.

Space charge accumulation within polymeric materials has been associated with their accelerated ageing. The measurement of this phenomenon can be used to correlate space charge profiles and their evolution to ageing. In this paper, accumulated charge depletion after long electrical ageing processes has been analyzed following a research trend pointed out in previous works. In order to extend this analysis to several materials, the electrically barely known UHMWPE (Ultra-high molecular-weight polyethylene), mostly used in medical applications, has been compared to well-known XLPE and LDPE. It has been proposed some extremely simple indicators that can be used to know the ageing of a polymeric insulation without incurring in simplifying assumptions and using only the charge profiles obtained directly from the space charge measurements taken by PEA (Pulse Electro Acoustic) method.

The integration of renewable energy sources (RESs) has become more attractive to provide electricity to rural and remote areas, which increases the reliability and sustainability of the electrical system, particularly for areas where electricity extension is difficult. Despite this, the integration of hybrid RESs is accompanied by many problems as a result of the intermittent and unstable nature of RESs. The extant literature has discussed the integration of RESs, but it is not comprehensive enough to clarify all the factors that affect the integration of RESs. In this paper, a comprehensive review is made of the integration of RESs. This review includes various combinations of integrated systems, integration schemes, integration requirements, microgrid communication challenges, as well as artificial intelligence used in the integration. In addition, the review comprehensively presents the potential challenges arising from integrating renewable resources with the grid and the control strategies used. The classifications developed in this review facilitate the integration improvement process. This paper also discusses the various optimization techniques used to reduce the total cost of integrated energy sources. In addition, it examines the use of up-to-date methods to improve the performance of the electrical grid. A case study is conducted to analyze the impact of using artificial intelligence when integrating RESs. The results of the case study prove that the use of artificial intelligence helps to improve the accuracy of operation to provide effective and accurate prediction control of the integrated system. Various optimization techniques are combined with ANN to select the best hybrid model. PSO has the fast convergence rate for reaching to the minimum errors as the Normalized Mean Square Error (NMSE) percentage reaches 1.10% in 3367.50 s.

Polymer, common insulating material, can be used with the metal layer. In order to investigate the reliability of its insulation performance, it is important to measure space charge by the pulsed electro-acoustic (PEA) method. However, it is difficult to measure space charge correctly because of the acoustic characteristic difference between the polymer and the metal layer. Therefore, we have proposed the numerical analysis model on PEA method for generation and propagation of acoustic wave in order to discuss the error factors in space charge measurement. In this paper, the results from the numerical analysis on the metal-polymer laminate material have proved that the metal material could have some influences on the results of space charge measurement.

The pulsed electro-acoustic (PEA) method is widely used to measure the space charge distribution through the thickness of solid dielectric materials. One of the well-known phenomena obtained by space charge measurement is the `packet charge' that is injected from one electrode and travels as a bulk to the other electrode. It has been observed as a bulk charge that moves inside the specimen, using a normal PEA system. We have developed a two-dimensional PEA system that can measure space charge profiles in a section of the specimen. By using this new two-dimensional PEA system, it was revealed that the `packet charge' is not homogeneous, and internal space charge behavior is more complicated than those described for bulk charge.

The pulsed electroacoustic (PEA) method is one of the useful electrical insulation evaluation technologies, which detects the space charge in the materials using the acoustic pressure wave. The space charge measurement was performed for an epoxy (EP) / Boron nitride (BN) insulating composite that is expected to be applied as a higher thermal conductive insulating material. The space charge profiles of EP/BN composite materials that cannot be explained by electromagnetic theory were observed. This controversial point appeared to be derived from the surface roughness of the sample, and there is a relationship between the surface roughness and the charge signal. The signal is adversely influenced by the surface roughness; therefore the sample which has smooth surface is required for the accurate space charge measurement of EP/BN composite.

Reports the results of an investigation into the space charge formation and decay at the interface between two layers of polyethylene. The influence of interface between electrode and polymer or polymer and polymer on the space charge formation and distribution has been studied. Planar samples were subjected to high dc electric stress for extended periods of time and space charge measurements taken using the pulsed electroacoustic (PEA) technique. It has been found that (i) types of interface between electrode and polymer play a significant role in determining charge distribution in the insulation, (ii) the interface between polymer and polymer acts as a potential barrier to electrons while allowing holes through easily.

Power grid stability has become an increasingly intricate challenge with the rising integration of renewable energy sources like wind and solar power. These energy sources, while essential for achieving sustainability goals, introduce significant variability and reduce the system’s inertia due to the displacement of conventional synchronous generators. This paper explores the combined role of High-Voltage Direct Current (HVDC) systems and the Kuramoto model in addressing these challenges. The Kuramoto model, traditionally used to study synchronization phenomena, is adapted to represent power system dynamics, enabling simulation of grid stability under diverse conditions. HVDC systems, with their ability to regulate power flows dynamically and reduce instability, are evaluated for their potential to mitigate fluctuations caused by renewable energy. Key topics include the theoretical underpinnings of grid stability, detailed simulation methodologies, experimental scenarios, and results showcasing HVDC’s stabilizing effects. Conclusions emphasize the synergy between advanced control systems and theoretical modelling, providing a pathway toward resilient and adaptable future energy networks. Key words. HVDC technology, Kuramoto-model, stability analysis of power systems

Polypropylene (PP)/elastomer blend is a promising candidate for high voltage direct current (HVDC) cable insulation. Space charge accumulation in HVDC cable is an important factor for safe and stable operation of HVDC transmission system. In this paper, propylene based elastomer (PBE) and ethylene-octene copolymer elastomer (EOC) were added into PP to prepare the blend sample. Space charge accumulation behavior was estimated by the pulsed electro-acoustic (PEA) method, and the influence of compatibility between the PP and the elastomer on the charge accumulation behavior was investigated. Polarized optical microscope (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) measurements were performed to assist the understanding of the compatibility dependent space charge accumulation behavior. The obtained results showed that the amount of space charge in the PP/PBE blend was lower than that in the PP/EOC blend. As compared with the PP/EOC blend, higher crystallinity with integrated crystal morphology and β-crystal form were observed in the PP/PBE blend for better compatibility between PP and PBE. It is suggested that deeper trap centers are formed in the PP/PBE blend than in the PP/EOC blend due to the compatibility, by which the charge injection is restricted.