Mitigation and control of electric fields on spacers' surfaces in gas insulated systems

Research in the area of gas insulated systems' (GIS) reliability is still attracting a considerable attention from the electric utilities and the scientific community in many countries. Solid insulating spacers in GIS represent the weakest points in these systems, and several troubles and systems' outages have been reported allover the world due to their failure. So it is essential to determine the electric field distribution along their surfaces and hence evaluate the degree of their reliability. Several researchers evaluated the electric field distribution on the spacers' surfaces in gas insulated systems and studied the effects of their dimensions and its relative permittivity on the electric field stress distribution. The outcome of these investigations is that the electric field stresses intensify around the triple junction and they are the main reason to initiate breakdown in gas insulated systems. Due to the previously mentioned spacers' troubles, they should be precisely designed to realize more or less uniform field distribution along their surfaces. The spacer's profile is considered the main variable, which controls the field distribution and hence field uniformity can be achieved by adopting the appropriate profile. This paper uses the artificial neural network technique "ANN" to optimize the electric field on the spacer's surface, and introduces a novel method based on replacing the spacer's material with a constant permittivity by another one having a functionally graded permittivity to optimize and control the electric field along its surface. The use of the ANN enabled the authors to design a spacer with a pre-selected almost uniform field along its surface. The error between the target field and the evaluated one is ± 5%. Also the use of FGM reduced the electric field near the triple junction at the enclosure to les than 50% in some cases

Laboratory Validation of Calculations of Magnetic Field Mitigation Underneath Transmission Lines Using Passive and Active Shield Wires

This paper is aimed at reporting experimental measurements and calculations of how the magnetic field underneath overhead transmission lines is mitigated using passive and active shield wires. The magnetic field values were compared to those calculated using the current simulation technique (CST). A laboratory transmission line model representing the Egyptian 500 kV EHV line was built with dimensions scaled down in the ratio 10:1. The flat single circuit of the line was modeled in the laboratory by phase separation of 1.2 m and conductor diameter of 2.76 mm at height of 1.9 m. The shield wires were spaced 4.3 m at a height of 1.45 m. Magnetic field measurements were carried out for load currents of 5.7 and 10 A. The field was measured at 0.3 m above ground level with and without passive and active shield wires for several different lateral positions. The measured and calculated field values generally agreed reasonably with an error ranging between 2.5 and 20 % within the ROW. The maximum reduction of magnetic field from the passive shield wires is 10% at the edge of right of way. With active shield wires carrying a current of 5 A (one half of the conductor current), the reduction of magnetic field reached 17% at the edge of ROW

Effect of solid spacers' dimensions and permittivity on the electric field distribution in gas insulated systems

In this paper, the effect of the spacer's dimensions and its relative permittivity on the total electric field distribution on its surface will be presented and discussed. These effects will be also outlined for a practical spacer's shape. The field behavior near the triple junction will be explained. Finally, an approximate empirical equation for the electric field distribution on the spacer's surface, taking into consideration all the parameters mentioned before, will be presented

Electric field distribution on insulating spacers in GIS using the finite element technique

Several failures in GIS systems have been reported in many installations around the world. A high percentage of these failures are due to improper design of the spacer's shape or manufacturing defects. In this paper a comprehensive study of the factors affecting the electric field distribution on the spacers' surface has been carried out. Three well known spacer's shapes have been investigated. The finite element method (FEM) has been used throughout the calculation in this paper. This method has proved to be accurate as other methods such as the charge simulation method (CSM). However, it does not need tedious trial and error methodology to select the proper number, location, and type of the simulating charges. The results presented in this paper show the effect of the various parameters of the spacer on the maximum value and distribution of the electric field. For the spacer's shape shown in (Fig.1-a), the electric field distribution is more or less uniform when the spacer's thickness (Zs) is 0.5 p.u., and the variation between the maximum and minimum electric field is about 2.4% (Fig.5). The relative permittivity of the spacer's material has a considerable effect on the field distribution on its surface. This effect increases the field near the high voltage electrode and decreases it near the earthed electrode (enclosure) for low values of permittivity. For high values of permittivity the effect is vice-versa. It is interesting to notice that the point of intersection of all curves occurs at the same point (Fig.10). For spacer's shape shown in (Fig.1-b), the electric field at the knee-point may reach double its minimum value (Fig.12). Also the electric field distributions on the upper and lower faces of the spacer's shape shown in (Fig.1-c) are presented. The tangential and normal field distributions on the spacer's surface are also reported in this paper. The spacer's shape and its dimensions are the main factors deciding the relative values of these fields

Effect of spacer's defects and conducting particles on the electric field distribution along their surfaces in GIS

Researches in the area of gas insulated systems (GIS) reliability are still attracting a considerable attention from the electric utilities and the scientific community in many countries. Solid insulating spacers in GIS represent the weakest points in these systems, and several troubles and systems' outages have been reported all over the world due to their failure. So it is essential to determine the electric field distribution along their surfaces and hence evaluate the degree of their reliability. This paper discusses the electric stress distribution at the solid-gas interface with spacer's defects and contaminating spherical conducting particles on the surface. The effects of the defect's size, type and its location and the particle's size and its location on the electric stress distribution at solid-gas interface are presented and discussed

Powerformers: a breakthrough of high-voltage power generators

Over the past couple of decades, changes have taken place in high-voltage insulation systems that have produced safer and more reliable operations. The mica/epoxy insulation, which has been used in rotating machines for over 100 years, is now being replaced by a new concept using high-voltage cross-linked polyethylene (XLPE) cables. Three new products have been recently launched including the Powerformer, a new generator that can be directly connected to the transmission network without the need for a step-up transformer. The other products include the Dryformer, an oil-free power transformer, and the Windformer, a new wind power generating system. Due to the Powerformer’s ability to generate electricity at transmission voltage levels, it offers considerable gains with respect to reactive power production and plant efficiency. Hence, a Powerformer both facilitates network stability and decreases the exploitation of natural resources. The upper limit for the output voltage from the Powerformer is set by state-of- the-art XLPE power-cable technology. Therefore, Powerformers revolutionize the age of old power generation technology and signal a quantum leap in electrical engineering

CORDIC-Based FPGA Realization of a Spatially Rotating Translational Fractional-Order Multi-Scroll Grid Chaotic System

This paper proposes an algorithm and hardware realization of generalized chaotic systems using fractional calculus and rotation algorithms. Enhanced chaotic properties, flexibility, and controllability are achieved using fractional orders, a multi-scroll grid, a dynamic rotation angle(s) in two- and three-dimensional space, and translational parameters. The rotated system is successfully utilized as a Pseudo-Random Number Generator (PRNG) in an image encryption scheme. It preserves the chaotic dynamics and exhibits continuous chaotic behavior for all values of the rotation angle. The Coordinate Rotation Digital Computer (CORDIC) algorithm is used to implement rotation and the Grunwald-Letnikov (GL) technique is used for solving the fractional-order system. CORDIC enables complete control and dynamic spatial rotation by providing real-time computation of the sine and cosine functions. The proposed hardware architectures are realized on a Field-Programmable Gate Array (FPGA) using the Xilinx ISE 14.7 on Artix 7 XC7A100T kit. The Intellectual-Property (IP)-core-based implementation generates sine and cosine functions with a one-clock-cycle latency and provides a generic framework for rotating any chaotic system given its system of differential equations. The achieved throughputs are 821.92 Mbits/s and 520.768 Mbits/s for two- and three-dimensional rotating chaotic systems, respectively. Because it is amenable to digital realization, the proposed spatially rotating translational fractional-order multi-scroll grid chaotic system can fit various secure communication and motion control applications

Evaluation of general public awareness, knowledge and attitude about common rheumatic diseases in Egypt: a multicenter study

Abstract Background Rheumatic diseases are the diseases of the connective tissue and medical disorders of the musculoskeletal system, with pain and/or stiffness as main manifestations, and which may or may not be accompanied by other organ system involvement. Public and patient’s awareness is needed as the number of patients of various forms of arthritis and other musculoskeletal diseases is constantly on rise. Objective The aim of our multicenter study is to evaluate awareness, knowledge, and attitude of general populations regarding common rheumatic diseases in Egypt. Subjects and methods This was a multicenter study included 3000 subjects from 4 Egyptian governorates (750 subjects from each): Lower Egypt: Dakahlia and Damietta and Upper Egypt: Sohag and Qena. Entire cases completed the Awareness, Knowledge, and Attitude of Egyptian people towards four of the common rheumatic diseases (Rheumatoid arthritis, Systemic lupus erythematosus, Crystal-induced arthritis, and Osteoarthritis): AKARSCO questionnaire that included basic information, general knowledge, and attitude about rheumatic diseases. Results The knowledge and awareness of rheumatic diseases are significantly higher among females. Regarding education level, there is a steady increase in the awareness with the rise of education level, with a highly significant correlation. Non-working and married participants had significantly higher knowledge compared to working and non-married ones. The attitude towards rheumatic diseases is significantly satisfactory among females. Regarding education level, there is a steady increase in the attitude with the rise of education level, with a highly significant correlation. Non-working and married participants had significant satisfactory attitude compared to working and non-married ones. The main sources of information about rheumatic diseases are media and Internet. Conclusion The overall awareness, knowledge, and attitude of population towards rheumatic diseases are limited in Egypt. The participants’ total score regarding the general knowledge level of rheumatic diseases, rheumatoid arthritis, SLE, gout, and osteoarthritis is bad. The participants’ overall level regarding the attitude towards rheumatic diseases is unsatisfactory. The level of knowledge and attitude is affected by many factors like sex, work, education, residence, marital status, and family history of rheumatic diseases. The main sources of information about rheumatic diseases are media and Internet

Impact of desflurane versus sevoflurane on coagulation in radical cystectomy patients

Background: Hypercoagulability in patients with cancer is difficult to detect through standard coagulation tests unless the platelet count and fibrinogen concentration is markedly increased. Reaching haemostasis during major surgical procedures is one of the most difficult problems which face anaesthesiologists. Objective: The aim of this study is to investigate the impact of desflurane in comparison to sevoflurane on coagulation detected by ROTEM to find out which of them is more suitable in reducing blood loss and better patient outcome after major surgery in the study population of patients. Patients and Methods: This study was conducted on thirty-six patients of both sexes having cancer bladder were admitted to Theodore Bilharz Research Institute (TBRI). They were randomly allocated into 2 groups (18 patients each). Group (S) received sevoflurane, while group (D) received desflurane as an inhalational anesthetic for Radical Cystectomy surgery. Six venous blood samples were collected for assessment of thromboelastometric parameters with INTEM, EXTEM, FIBTEM analysis which were CT (clotting time), CFT (clot formation time), α angle and MCF (maximum clot firmness)