This paper concerns the definition and evaluation of less-flammable of insulation fluids for transformers. In particular it focuses on the ISO5660 cone calorimeter method, which is widely used as an evaluation method for the less-flammable of solids, and proposes that such method is also valid for quantitative evaluation of the less-flammable of insulating fluids. Quantifying the combustion characteristics of insulation fluids and analyzing the causes of fires can be said to be the first step toward implementing appropriate safety measures that will render electric utility equipment more fire retardant or fireproof in the future.
This paper presents a cooperative allocation method of Step Voltage Regulators (SVRs) and Static Var Compensators (SVCs) in case where some distributed generators (DGs) are installed in distribution systems. In the proposed method, the reactive tabu search (RTS) with multiple structures and functions has been applied. Firstly, the allocations of SVRs are selected optimally and secondly the tap positions of SVRs are optimized by the RTS. Finally, the locations of SVC are decided to brush up the voltage profile in the distribution network. The proposed method enables us to take account of the installation cost of both SVR and SVC as an economic criterion, the upper and lower limit of voltage at each node, and also the upper limit of line currents as constraints. By applying the proposed method to a practical distribution test system (IEEE 34 Node Test Feeder Model), it is verified that this method is efficient in allocating SVRs and SVCs at the minimum cost and to regulating the system voltages within an appropriate value after introducing distributed generators into the distribution system.
This paper presents a method for tuning of power system stabilizers (PSS) for damping low-frequency oscillations in a multi-machine power system based on the wide area phasor measurement. The authors have developed a method for detecting inter-area low-frequency modes from the measured small oscillation associated with the load fluctuation by approximating oscillations as a coupled vibration model. In this paper, the coupled vibration model is extended for including the effect of PSSs. PSSs are tuned directly by using the extended model since the model includes parameters of PSSs. The advantage of this method is that steady state phasor fluctuations are available to tuning PSSs and assess the effect of the tuning control. In other words, a large disturbance like a line fault is not necessary since the stability of the major modes can be investigated directly by using eigenvalues of the extended model. The identification process does not require the information on the input to the system for perturbation. Some numerical analyses demonstrate the effectiveness of the method by using phasor dynamical data obtained by a power system simulation package.
“DC Micro-grid" is a novel power system using dc distribution in order to provide a super high quality electric power. The dc distribution system is suitable for dc output type distributed generations such as photovoltaic and fuel cells, and energy storages such as batteries and electric double layer capacitors. Power is distributed through dc distribution line and converted to required ac or dc voltage by converters placed near loads. The load side converters do not need transformers by choosing proper distributed dc voltage. The spread scheme of converters contributes to provide a high quality power supplying. Even if a short circuit occurs at one load side, it does not effect other loads. In this paper, we propose a configuration of DC micro-grid and control methods of converters for generations and energy storages. Computer simulation results demonstrated the seamless operation during turn-on and turn-off of a distributed generation, the transient of connecting and disconnecting operation with bulk power system, and the stability against a sudden large load variation.
In this study, adaptive PSS using measurable state variables at generator buses is developed. The PSS parameters are tuned based on eigenvalue analysis for a low-order simple linear model of each generator obtained by identification. The low-order model consists of block diagram of PSS and relationship from output of PSS to input of PSS with limited variables which are identified by least squares method using ΔPe and Δω measured at each generator bus. The identification for the PSS parameter tuning is repeated. The PSS parameters are tuned every second to keep power system stable. Digital simulations for transient stability analysis are carried out for IEEJ WEST 10-machine system model. It is made clear that the stability is improved only when dominant oscillation is identified at generator bus.
This paper proposes a new load monitoring system of electric appliances based on Hidden Markov Model. Monitoring of electric appliances under operation is expected to lead to understanding needs of power consumers and forecasting power demands in future. When a certain electric appliance runs, the current waveform flowing in it shows specific characteristics. Therefore, it is quite reasonable to pay attention to the pattern of current waveforms for recognition of used electric appliances. In this paper, Hidden Markov Model, which is widely used for the analysis of time series data, is introduced as the recognizer for the current waveforms. The usefulness of the proposed method is verified through some experiments using real measured data.
In order to obtain good wind conditions, wind turbine generation systems are built at places like hill countries and shorefronts where few tall structures are found. However, this increases the risk of lightning strikes. To promote wind power generation, lightning-protection methodologies for such wind turbine generation systems have to be established. This paper presents the results of an experimental study which investigates the lightning overvoltages in wind turbine generation systems. The experiments were carried out on actual ground soil using a reduced-size wind turbine model with its foundations. From the experiments, the following conclusions have been deduced: (i) Voltage rise due to the grounding impedance of the foundations can cause a significant overvoltage between the tower foot and an incoming cable like a power, a communication or a control line. (ii) The voltage rise of the foundations and that of the surrounding ground soil may cause an overvoltage at the outermost insulation layer of an incoming cable, which can result in a breakdown or a deterioration of the insulation (iii) Voltage and current waveforms to understand the traveling-wave phenomenon on a wind power generation system with its foundations were obtained. The data will be useful for developing an EMTP simulation model of a wind turbine generation system for lightning overvoltage studies.
We studied a new wind turbine system that uses an electric double layer capacitor (EDLC) as a method of effectively producing hydrogen from natural energy. Before this system can be installed and its effects considered, an outline design of the system based on the wind conditions in the installation region must be performed, and the system scale and the obtained amount of the electric power must be estimated. In this paper, the method to determine the system configuration that would effectively supply the electric energy to the hydrogen generator was examined using numerical analysis. The configuration obtained from this analysis determined the required capacity of the hydrogen generator for the amount of power generation that was needed, as well as the conditions required in order for the EDLC to effectively buffer any changes. When a system is constructed using this configuration, the electric charging and discharging of the EDLC are balanced, and it is possible to effectively supply electric energy to the hydrogen generator. When a wind turbine generator with a rated power of 500W was operated under the wind conditions on Miyako Island, the appropriate capacity of the hydrogen generator was 144W, and the corresponding EDLC capacity was 11.3Wh.
We propose the new locating method for multiple partial discharge sources using independent component analysis (ICA) and direction of arrival method of electromagnetic (EM) waves based on Bayesian Network. The proposed method consists of the following steps. First, the observed signals are converted from the time domain to the frequency domain through the short time Fourier transform (STFT). As the result of this process, ICA for convolved mixture turns into ICA for instantaneous mixture. In order to separate mixed signals, we use the fast ICA algorithm (FastICA) that is based on negentropy as a measure of nongaussianity. Next, we apply the direction of arrival method of EM waves using Bayesian Network to the separated source signals by ICA. Signal sources are estimated by calculating intersection point from the arrival angle. Simulation results showed that our method located multiple signal sources when the observed signals were the convolved mixture of original sources.
In this study, we found that the reflective absorbance correlates with the average degree of polymerization of the insulating paper, the correlation coefficient being over 0.90. It was found out that the optical diagnostic method could be applied in the core degradation diagnosis of a pole transformer, and the indirect degradation diagnostic apparatus of the pole transformer using this technique was developed. Optical diagnostics is a method of analysis by presuming the degree of proceeding of the heat deterioration of the organic insulator from the difference in reflective absorbance of two wavelengths containing near-infrared light, and the life prediction is also possible by using chemical kinetics. In this diagnosis, the degree of deterioration of the insulating paper can be calculated quantitatively using the diagnostic master curve, which is obtained from accelerated heating experiments based on the chemical kinetics. The optical sensor consists of two kinds of optical fiber cables to attach and measure the reflective absorbance on the insulating papers in the oil, two kinds of near-IR (infrared) laser diodes (LD), 830nm and 1310nm, as light sources, and a photodiode as a detector, and so it is very compact and lightweight (less than 1.5kg).
In relation to the accidents due to bird nests in contact with overhead distribution lines, the authors investigated on deterioration of covered conductor by corona discharge. To simulate the situation where conductive nest material such as wire is in contact with both of an arm and a covered conductor, a copper wire was wound around the covered conductor and was grounded through a resistor which is used to observe corona discharge current waveform. The state of normal operation of 6.6kV distribution line was considered and A.C. 3.8kV was applied between the conductor and the ground. Weak corona discharge was observed. In order to carry out the acceleration test, A.C. 6.6kV was applied. The insulation was punctured after 3760 hours. From the observation of cumulative charge by corona discharge the acceleration factor was estimated about 4. From the acceleration factor estimated, the life of conductor cover will be 627 days.
The Metal Hydride Intermediate-Buffer (MIB) method has been proposed as a measure to enable flexible load following operation and immediate start-up of PEFC system with a reformer. In this method, using the property of metal hydride to absorb hydrogen selectively, hydrogen is stored and purified simultaneously from reformed gas with impurities and subsequently supplied to PEFC stack. In this paper, using the fluorinated LmNi4.4Mn0.3Al0.3 metal hydride, we have investigated to improve resistivity of the metal hydride against CO to simplify the reformer. If the resistivity against CO rises to the 1%, preferential oxidation (PROX) process in reformer can be removed. Important consideration in this method is to keep CO concentration of released hydrogen from metal hydride below 10ppm. To investigate the effect of CO, absorption and release experiments of hydrogen from simulated reformed gas containing 100, 1000ppm or 1% CO were carried out with the specimen. The result of the absorption experiment shows that, when the specimen temperature is set to 50°C or higher, hydrogen absorption rate remains nearly unaffected by existence of 1% CO. The result of the release experiment shows that, when the specimen temperature exceeds 120°C, CO concentration of released hydrogen is approximately kept below 10ppm.
This paper describes the development for ZCT sensor that enabled the flexible change of own size and shape. The proposed ZCT sensor is consist of the loop of plural pieces of the magnetic-induction units with the core and coil. The magnetic-induction unit has the rotational axes at the both end which enabled the easy change of ZCT window size and own shape by increasing or decreasing the number of units. Also, the internal residual current of ZCT sensor can be reduced by connecting the coils in parallel. The residual current (primary current level) of less than 50mA is achieved for zero phase sequence current at 600A primary load current.
Recently an electromagnetic actuator has been widely used as an operating mechanism for the vacuum circuit breaker (VCB). The opening velocity of the contact is supposed to be strongly related with current interruption performance. This paper presents a simple and new technique that raises opening velocity of the electromagnetic actuated VCB. In order to investigate this reason, we built a numerical simulator that predicts the dynamic characteristics of the VCB contact. It takes into account of the magnetic behavior in the actuator and is also coupled with the external control circuit. According to this simulation, it is shown that it is originated from the sharp rise in the electromagnetic thrust force due to the selective saturation of the magnetic yoke. As the result of our experiments, by this technique the opening velocity was verified to be 1.5 times faster than by the conventional way.
The high frequency oscillation in voltage transformer is analyzed using an equivalent lumped circuit with FFT method. Such analysis has been regarded difficult since those used in high voltage distribution systems have a large number of turns. The constants of equivalent circuit are evaluated on turn-to-turn basis. The frequency domain analysis is followed by the time domain using FFT technique. The both characteristics are verified by the experiment on a 6.6kV voltage transformer. The nature of high frequency oscillation is shown for a simpler model. It is found the interlayer voltage is highest at the entrance of incoming surge.
In order to rationalize the lightning protection design of distribution lines, lightning phenomena on TEPCO's distribution lines has been continuously observed. The observation has been carried out with still cameras and monitoring sensors of lightning surges. The result clears the features of lightning performance of distribution lines. For example, direct lightning strokes are the major cause of present distribution line faults. This fact suggests that it is important to investigate observation data of a direct lightning stroke. In this study, the paper analyzed the observation data based on a direct lightning analysis model. The calculated waveforms were compared with the measured waveforms of the observation in distribution lines. Moreover, probability distributions of surge current and voltage were calculated with the Monte Carlo method. These results provided new data on lightning performance.
Impulse voltage calibration is specified in IEC 61083-1 as a reference calibration method for the digital recorder used in the impulse voltage measuring system. Uncertainty of the calibrator needs to be specified to calibrate the digital recorder. The national standard class calibration system for the impulse voltage was developed in 2001 in Japan. At that time, the uncertainties of the wave shape parameters of its outputs were evaluated. The long term stability of the calibrator has been measured for five years, and the uncertainties of the system are re-evaluated this time. In this letter, the estimation method of the uncertainty and re-evaluated uncertainties of the calibration system are described.