sulation performance of gas-insulated switchgear (GIS). In order to establish highly sensitive diagnosis techniques of GIS insulation, fre- quency characteristics ...
Abstract: Partial discharge (PD) measurement using electromagnetic waves by antennas is a promising technique for diagnosing the insulation performance of gas-insulated switchgear (GIS). In order to establish highly sensitive diagnosis techniques of GIS insulation, frequency characteristics of electromagnetic waves, which are determined by GIS apertures such as insulating spacers and bushings, should be clarified. In this paper, we measure the electromagnetic waves radiated from different GIS apertures and also analyze them using the transient analysis program "PSpice." Comparing the measurements with the theoretical analyses, we investigate the relationship between the GIS aperture configuration and the radiated electromagnetic wave spectrum from the aperture. We also discuss how the aperture condition contributes to the radiation characteristics of electromagnetic waves. Finally, we conclude that the electromagnetic waves radiated from the GIS aperture are based on different radiation mechanisms in frequency. Keywords: GIS, radiated electromagnetic waves, spacer aperture, transient analysis, frequency spectrum. Preprint Order Number: PE-030PRD (04-2001) Discussion Deadline: September 2001
A Novel Technique for Detecting Electromagnetic Waves Caused by Partial Discharge in GIS Hoshino, T.; Kato, K.; Yayakawa, N.; Okubo, H. Author Affiliation: Department of Electrical Engineering, Nagoya University, Nagoya, Japan Abstract: For the insulation diagnosis of gas-insulated switchgear (GIS), it is necessary to detect partial discharge (PD) under noisy conditions and to specify the direction of electromagnetic wave radiation due to PD. We propose the "phase gate control method" for discriminating the electromagnetic waves caused by PD in SF6 gas from external noises. The proposed method enables us to discriminate PD of about 100 pC in SF6 gas from external noises of more than 10,000 pC in air. We also compare polarization characteristics of electromagnetic waves radiated from PD with those from a half-wave dipole antenna and estimate the radiation length of electromagnetic waves caused by PD. The results derived in this paper will contribute greatly to the insulation diagnosis of GIS on site. Keywords: GIS, PD, noise elimination, polarization, electromagnetic wave spectrum. Preprint Order Number: PE-080PRD (04-2001) Discussion Deadline: September 2001
Transformers Other Factors Contributing to the Core Loss Performance of Power and Distribution Transformers TeNyenhuis, E.; Girgis, R.; Mechler, G. Author Affiliation: ABB Electrical Systems Technology Institute; ABB Power T&D Company Inc.; ABB Corporate Research Abstract: This paper presents results of analytical and experimental studies that give insight into the nature and mechanism of the generation of localized losses in the core joints, losses caused by core stacking holes, and the increase of iron loss of the core material due to slitting. These three loss components alone have been found to contribute about 3-4% to the total no-load loss of a large power transformer and as much as 10% in a small distribution transformer. The results show how the magnitude of these loss components varies with operating flux density, core material, excitation frequency, and geometrical
parameters of the core. Keywords: Core loss, additional localized joint loss, holes, slitting, transformer. Preprint Order Number: PE-049PRD (04-2001) Discussion Deadline: September 2001 70
A Novel Approach to the Classification of the Transient Phenomena in Power Transformers Using Combined Wavelet Transform and Neural Network Mao, P.L.; Aggarwal, R.K. Author Affiliation: University of Bath, U.K. Abstract: The wavelet transform is a powerful tool in the analysis of the power transformer transient phenomena because of its ability to extract information from the transient signals simultaneously in both the time and frequency domain. This paper presents a novel technique for accurate discrimination between an intemal fault and a magnetizing inrush current in the power transformer by combining wavelet transforms with neural networks. The wavelet transform is first applied to decompose the differential current signals of the power transformer into a series of detailed wavelet components. The spectral energies of the wavelet components are calculated and then employed to train a neural network to discriminate an intemal fault from the magnetizing inrush current. The simulated results presented clearly show that the proposed technique can accurately discriminate between an intemal fault and a magnetizing inrush current in power transformer protection. Keywords: Power transformer, fault detection, magnetizing inrush current, wavelet transform, artificial neural network. Preprint Order Number: PE-098PRD (04-2001) Discussion Deadline: September 2001
Frequency Characteristics of Single-Phase Two-Winding Transformers Using Distributed Parameter Modeling AlFuhaid, A.S. Author Affiliation: Kuwait University, Kuwait Abstract: Using modal analysis and modeling results from transmission-line theory, closed-form s-domain expressions are derived for the spatial voltage and current distributions along the primary and secondary windings of a single-phase two-winding transformer. These expressions take into account both of the inductive and capacitive couplings between the two windings, in addition to intertum coupling within each winding. The frequency characteristics of the transformer input impedance under different loading conditions are obtained, which can be useful in identifying the resonant frequencies of the transformer. The results are compared with those obtained from the well-known circuit simulation program SPICE. Keywords: Power transformers, frequency-domain methods, frequency characteristics. Preprint Order Number: PE-O15PRD (04-2001) Discussion Deadline: September 2001
Diagnosing Failed Distribution Transformers Using Neural Networks Farag, A.S.; Mohandes, M.; Al-Shaikh, A.
Author Affiliation: King Fhad University of Petroleum & Minerals, Dhahran, Saudi Arabia; SCECO-East/ EDSD-EED, Dammam, Saudi Arabia Abstract: An artificial neural network (ANN) system was developed for failure diagnosis of distribution transformers. The diagnosis was based on the latest standards and expert experiences in this field. The ANN was trained utilizing the back propagation algorithm using, real (out of the field) data obtained from transformer failures of utility distribution networks. The ANN consists of six individual ANN according to six important factors used to give certain outputs. These factors are: the age of the transform, weather conditions, damaged bushings, damaged casing or enclosures, oil leakage, and faults in the windings. The six ANNs are combined in one ANN to give all the outputs of the individual six ANNs. The developed ANN can be used to give recommended complete diagnosis for working transformers to avoid possible failures depending on their operating conditions. Good IEEE Power Engineering Review, July 2001
diagnosis accuracy is obtained with the proposed approach applied and with the analysis of the attainable results. Preprint Order Number: PE-920PRD (04-2001) Discussion Deadline: September 2001
A Comparative Study of Neural Network Efficiency in Power Transformers Diagnosis Using Dissolved Gas Analysis Guardado, J.L.; Naredo, J.L.; Moreno P.; Fuerte, C.R. Author Affiliation: ITM; CINVESTAV Abstract: This paper presents a comparative study of neural network (NN) efficiency for the detection of incipient faults in power transformers. The NN was trained according to five diagnosis criteria commonly used for dissolved gas analysis (DGA) in transformer insulating oil. These criteria are Doemenburg, modified Rogers, Rogers, IEC, and CSUS. Once trained, the NN was tested by using a new set of DGA results. Finally, NN diagnosis results were compared with those obtained by inspection and analysis. The study shows that the NN rate of successful diagnosis is dependant on the criterion under consideration, with values in the range of 87-100%. Keywords: Power transformer testing, neural networks, fault diagnosis. Preprint Order Number: PE-063PRD (04-2001) Discussion Deadline: September 2001
Transmission and Distribution Modeling and Prediction of Distribution System Voltage Distortion Caused by Nonlinear Residential Loads Wang, Yj.; O'Connell, R.M.; Brownfield, G. Author Affiliation: University of Missouri, MO; Ameren Services Abstract: Electric utilities have expressed concern over increased nonlinear loading of residential power distribution systems. The number and variety of power electronic products found in the typical home continues to grow rapidly, imposing a burden on local power companies to supply reliable, distortion-free service. In order to adequately prepare for the future, utilities must be able to predict the harmonic impact of new power electronic equipment and evaluate the ability of existing power systems to accommodate these nonlinear loads. This paper describes a modeling methodology that uses SPICE simulation software to predict the voltage distortion caused by nonlinear residential loads. Results of applying the methodology to a specific distribution system containing either of two different types of harmonic-rich loads, i.e., variable-speed air conditioners or electric vehicle battery chargers, are presented as well. Keywords: Harmonic currents, voltage distortion, power distribution system, nonlinear residential load. Preprint Order Number: PE-203PRD (04-2001) Discussion Deadline: September 2001
36 Pulse HVdc Transmission for Remotely Sited Generation Villablanca, M.; delValle, J.; Urrea, C.; Rojas, W. Author Affiliation: University of Chile, Chile; SERVINSUM Ltda. Abstract: Remotely sited generators that are connected to load centers may economically use HVdc transmission. The possibility of connecting the generators directly to the HVdc converter station, with both ac and dc filters removed, has been discussed frequently in the past, with significant capital and operating savings argued but as yet without such a system being realized. It would seem that the removal of filters is not feasible. In this paper a 36-pulse operation for the converter station is proIEEE Power Engineering Review, July 2001
posed, whereby substantial reduction of harmonics is achieved and thus both ac and dc filters may be removed without further implications. Keywords: HVdc transmission, group connection, HVdc converters, harmonics, filters, hydro electric generation. Preprint Order Number: PE-002PRD (04-2001) Discussion Deadline: September 2001
Modular Active Power-Line Conditioner El Shatshat, R.; Kazerani, M.; Salama, M.M.A. Author Affiliation: University of Waterloo, Ontario, Canada Abstract: Active power-line filtering is conventionally performed by injecting equal-but-opposite of the distortion into the line. The power converter used for this purpose is rated based on the magnitude of the distortion current and operated at the switching frequency dictated by the desired filter bandwidth. Fast switching at high power, even if technically possible, causes high switching losses. In this paper, a new modular approach to active harmonic filtering is proposed. The method utilizes two linear adaptive neurons (ADALINEs) to process the signals obtained from the line. The first ADALINE (the current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of both ADALINEs are used to construct the modulating signals of a number of current-source inverter (CSI) modules, each dedicated to eliminate a specific harmonic. The power rating of the modules will decrease and their switching frequency will increase as the order of the harmonic to be filtered is increased. The overall switching losses are minimized due to the selected harmonic elimination and balanced "power rating"-"switching frequency" product. Power losses are also reduced by adjusting the Id, in each CSI module according to the present magnitudes of the individual harmonics to be filtered. Speed and accuracy of ADALINE; self-synchronizing harmonic tracking; optimum Idc value and minimal converter losses; high reliability, flexibility, and speed; and low dc energy requirement of the CSI result in superb performance of the proposed active conditioner. The theoretical expectations are verified by digital simulation using the EMTDC simulation package. Keywords: Active power filter, ADALINE, CSI, EMTDC. Preprint Order Number: PE-071PRD (04-2001) Discussion Deadline: September 2001
Temperature Adaptive Switching Operation for Distribution Systems Chen, C.S; Kang, M.S.; Hwang, J.C.; Huang, C.W. Author Affiliation: National Sun Yat-Sen University; National Kaohsiung Institute of Technology; Power Research Institute Abstract: This purpose of this paper is to investigate the optimal switching problem of distribution systems by considering the customer load characteristics and the effect of temperature change on customer loading. The load survey is applied to derive the typical load patterns of residential, commercial, and industrial customer classes. The power consumption of sample test customers and weather information are used to solve the hourly temperature sensitivity of power consumption for each customer class. All the customers served by each distribution transformer are identified and their monthly energy consumption is retrieved from the customer information system in Taipower. The hourly loading of each service zone and its change due to temperature rise are obtained based on the customer load consumption and its temperature sensitivity. By performing the connectivity trace to find the feeder configuration and executing the three-phase load flow analysis, the hourly current loading of line switches, distribution feeders, and main transformers in substations is solved. The binary integer programming is then applied to determine the temperature adaptive optimal switching operation for noninterruptible load transfer among distribution feeders and main transformers.
Keywords: Load model, binary integer programming, temperature
sensitivity, optimal switching operation. Preprint Order Number: PE-5 1OPRD (04-2001) Discussion Deadline: September 2001
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