We have obtained the electric current, electric field change, and optical image data or several tens of lightning that hit on a wind turbine and its lightning-protection tower during the past6 non-stop winter seasons from 2005 to 2010. By analyzing the data, we found that the upward lightning hitting on the high structures can be classified into self-initiated and other-triggered types according to whether there is a discharge activity prior to the upward lightning. We also found that although other-triggered upward lightning can start at a relatively lower wind speed, self-initiated upward lightning always started either from the stationary tower under a larger wind speed or from a rotating wind turbine blade. It appears that the wind and by inference the corona discharge shielding do have considerable effect in the initiation of an upward leader. Regarding the initial progression of a positive leader, we found a systematic difference in the speeds of the leaders from the structures that have remarkably different heights. Finally, we discussed the pulse discharges observed in the very initial stages of positive upward leaders and also how to forecast direct strike of upward lightning.
This paper presents a new approach to deal with the problem of robust tuning of power system stabilizer (PSS) and automatic voltage regulator (AVR) in multi-machine power systems. The proposed method is based on a model predictive control (MPC) technique, for improvement stability of the wide-area power system with multiple generators and distribution systems including dispersed generations. The proposed method provides better damping of power system oscillations under small and large disturbances even with the inclusion of local PSSs. The effectiveness of the proposed approach is demonstrated through a two areas, four machines power system. A performance comparison between the proposed controller and some of other controllers is carried out confirming the superiority of the proposed technique. It has also been observed that the proposed algorithm can be successfully applied to larger multiarea power systems and do not suffer with computational difficulties. The proposed algorithm carried out using MATLAB/SIMULINK software package.
The Energy management systems (EMS) on demand sides are expected as a method to enhance the capability of supply and demand balancing of a power system under the anticipated penetration of renewable energy generation such as Photovoltaics (PV). Elucidation of energy consumption structure in a building is one of important elements for realization of EMS and contributes to the extraction of potential energy saving. In this paper, we propose the estimation method of operating condition of household appliances using circuit current data on an electric distribution board. Circuit current data are broken down by their shape using a self-organization map method and aggregated by appliance based on customers' information of appliance possessed. Proposed method is verified using residential energy consumption measurement survey data.
The symmetric coordinates are very popular method to model unbalanced faults in power system analysis. It is not only easy to handle with a single fault, but also it can be extended to multiple faults. But it is not easy to model situations that those unbalanced situation will continuously change, like a SVC (Static Var Compensator) with unbalanced fault in power system or an unbalanced nonlinear load. Under these situations, we propose a practical use of multiple fault calculation method based on symmetric coordinates that can handle with these kinds of unbalanced situations.
This paper presents a new method for estimating unknown parameters of dynamic load model as a parallel composite of a constant impedance load and an induction motor behind a series constant reactance. An adequate dynamic load model is essential for evaluating power system stability, and this model can represent the behavior of actual load by using appropriate parameters. However, the problem of this model is that a lot of parameters are necessary and it is not easy to estimate a lot of unknown parameters. We propose an estimating method based on Particle Swarm Optimization (PSO) which is a non-linear optimization method by using the data of voltage, active power and reactive power measured at voltage sag.
It can happen to change system configurations even during the normal conditions in order to meet the demand for electric power. We expect every configuration transitioning from the original system to the target one to be secure from the view point of power supply reliability. Therefore, it becomes more important to make a feasible system configuration by adequately selecting switching operations. In this paper, we propose a new framework for drawing up switching operation procedures considering power supply reliability. It deals with a problem for determining a sequence of transition configurations which are obtained from candidates for outage planning which the authors have so far proposed. We also provide simulation results to demonstrate the effectiveness of the proposed method.
This paper describes an experimental study concerning the pressure-rise due to the high current arcs in a closed chamber. In this study, the arcs were ignited in certain chambers of varying size under the same conditions, namely, the arc current of 12.5kA and the arc duration of 0.1s. Moreover, the pressure-rises in the chambers were measured with changing the current waveform, namely, the frequency of the AC power source and the DC component of the current, and the ignition position. Based on each measured waveform of them, not only the maximum value ΔPmax but also the middle value ΔPmid, which was a middle of the amplitude around the time point of ΔPmax, were extracted. As a result of the evaluation using both ΔPmax and ΔPmid, it was clarified that ΔPmax/ΔPmid varied with both the current waveform and the ignition position, whereas ΔPmid was independent of them. Through FFT analysis of both the pressure-rise and the arc power waveforms, it was verified that this experimental result was related to the resonance effect between the pressure-rise and the arc power oscillations.
When a dc voltage is applied to an insulating spacer, the electric field distribution around it is determined by the resistivity of the material. Consequently, charges are accumulated on the surface of the insulator, and the breakdown voltage of it may become low. In this paper, the charge density distribution of the insulator is measured. The measured data indicate that the surface conductance is the main factor of the charge accumulation. Therefore, the conductivity of the insulator is also measured, and the influence of the surface conductivity on the charge accumulation is examined from both sides of experiment and numerical computation. It is confirmed that nonuniformity in the surface conductivity is responsible for the charge accumulation and the conductivity of insulator in atmospheric pressure SF6 is estimated to around σ = 1×10-18Ω-1.
With the progress of the information-oriented society, telecommunication lines are often installed on concrete poles along with power distribution lines. When a lightning stroke hits a distribution pole, the lightning current flows also through the telecommunication line in addition to the concrete pole and the ground wire. And, it is easily estimated that the existence of the telecommunication line reduces the currents through the concrete pole and the ground wire, and thus, reduces the voltage across the insulators to support the phase wires. However, its quantitative study has not yet been carried out. Considering the above, we have measured the surge impedance matrix of an actual-scale test distribution line equipped with a telecommunication line. Using this result, a method to model the distribution line system with the telecommunication line for lightning overvoltage simulations is proposed in this paper. Simulation results obtained by the proposed modeling method are compared with field-test results, and good agreement is obtained.
A Rogowski coil, used for measuring lightning current through a wind turbine generator system, is generally set up at the foot of a tower. In most wind turbines, there is an entrance at the foot of the tower, which leads to a flight of stairs or a ladder. When lightning strikes the wind turbine, the lightning current flows to the ground through the blades, nacelle, and tower. The current is shunted to the tower and the stairs/ladder at the foot of the tower, from where it may flow into the foundation and the earth. A Rogowski coil is usually set up at only the foot of a tower. The lightning current shunted to the stairs/ladder cannot be measured using the Rogowski. The installation position of the Rogowski coil depends on the construction of the stairs/ladder. In this study, the lightning current distribution at the foot of a tower is calculated using the FDTD (Finite Difference Time Domain) method, which is one of methods used for numerical analyses of electromagnetic fields. We also studied the effect that the setup of the stairs/ladder and the resistivity of the ground have on the lightning current distribution. The results of the current distribution are very important for predicting the total current that flows through an existing wind turbine generator system.
Influence of polymer ablation on arc properties such as temperature distribution and arc conductance in current decay process was investigated by numerical approaches. A numerical thermofluid model was developed for a simplified circuit breaker with POM or PTFE ablation. In this model, thermal plasma-polymer solid coupling phenomena such as melting and evaporation were taken into account without any empirical model based on measurements unlike other existing numerical thermofluid model. Dominant process for decay of arc conductance was examined by changing thermodynamic parameters such as melting and boiling temperatures of solid polymers, or thermal conductivity and electrical conductivity of ablation gas. As a result, it was found that gas density, thermal conductivity and electrical conductivity of ablation gas were more effective for decaying arc conductance than any other thermodynamic parameters.
So far, as a part of NaBH4-H2-Fuel Cell study we have been through optimization of hydrogen production reactor size and operating conditions to reach 100% of hydrogen production rate. Moreover, the potential of NaBH4-H2-Fuel Cells were verified by testing a 1000mL pressurebuffer for steady hydrogen supply under variable load conditions within maximum limit of 1.2kW. However, the buffer used gives rise to decreased energy density of the system due to its big size relatively to other components. Hence, minimized buffer volume under the limit of applied conditions is required to compact the system. In this study, the pressurebuffer volume which satisfies load following as well as compact size is found. Load following ability is approved as a result of hydrogen generation system operation, which has 325mL and 170mL buffer volume at 0°C and 20°C respectively within load variation of the average load 700W, peak load 1200W and 2 seconds of load cycle. Furthermore, NaBH4-H2-Fuel Cell's energy density is calculated. At last, all these come into the result that NaBH4-H2-Fuel Cell has high usefulnessas a high density mobile power source over 2.7kWh.
Insulation behavior of small-air-gap for the molded insulation system has been investigated by comparing the well-known Paschen curve. Three electrode systems Metal-Gap-Metal (MGM), Metal-Gap-Insulator (MGI) and Insulator-Gap-Insulator (IGI) were employed as the test samples. It was found that Vs (breakdown voltage of the air gap) of the MGM were higher than the conventional Paschen curve, which can be attributed to the lacked initiating electron for Vs. This behavior was also obtained for MGI and IGI system. However, X-ray irradiation gives the remarkable effect on these Vs resulting in the coincidence to the Paschen data. According to the references' data-review and some experimental data for Paschen minimum region, new fundamental and universal Paschen curve for the solid insulation system was proposed.
In today's highly information-based society, lightning damage has a significant impact on an increasing number of electric appliances such as personal computers and facsimile machines. Lightning surge protection devices for electric appliances are on the market and concern for lightning protection has been increasing, but there are still many unknown aspects of lightning surges that propagate into residences. To provide effective lightning protection measures, clarification of surge propagation patterns is needed. The Tokyo Electric Power Company has observed the patterns of lightning surge propagation into houses using lightning surge waveform detectors installed at ordinary residences and obtained data on 30 lightning surge current waveforms between 2008 and 2009. This paper discusses various aspects of lightning surge currents propagating into low-voltage appliances, including home electric appliances, based on the lightning surge current waveform data obtained from lightning observations. The result revealed the patterns of lightning surge currents propagating into the ground and lines of low-voltage appliances.