Power system simulations are roughly classified into the two categories, effective-value-based simulations and electromagnetic transient simulations. The former are usually long-term simulations of a large power system considering the electro-mechanical dynamics and include for instance transient stability simulations. On the other hand, the latter are basically short-term simulations of a small portion of a power system, and surge simulations and power-quality simulations are included. However, for simulations which contain power-electronics controllers, electromagnetic transient simulation methods are often used even for long-term simulations. This paper first reviews various programs for electromagnetic transient simulations, and then the recent trend of related simulation techniques is summarized.
This paper describes the improving method of Rogowski coil for the measurements of zero-phase-sequence current. For the measurements of zero-phase-sequence current, the error made by the influence of external magnetic field and residual current is explained and verified in this paper. In new winding method, two wires are used to wind with different winding directions at the start. This winding method makes the crossing point at the opposite side of the coil, and two wires should be crossed up and down alternately to form the same size of cross section of the coil. The coil is divided to several pieces of small coils. The outputs of these coils are connected in parallel. It is observed that the influence of external magnetic field and residual current is improved tremendously by this new improvement.
In this paper, we show an autonomous dispersed control system for independent micro grid of which performance has been substantiated in China by Shikoku Electric Power Co. and its subsidiary companies under the trust of NEDO (New Energy and Industrial Technology Development Organization). For the control of grid interconnected generators, the exclusive information line is very important to save fuel cost and maintain high frequency quality on electric power supply, but it is relatively expensive in such small micro grid. We contrived an autonomous dispersed control system without any exclusive information line for dispatching control and adjusting supply control. We have confirmed through the substantiation project in China that this autonomous dispersed control system for independent micro grid has a well satisfactory characteristic from the view point of less fuel consumption and high electric quality.
In recent years, it has become increasingly important to consider distributed resources, high efficiency operation and maintaining power quality in the distribution network. It is necessary to utilize the measured value of the network voltage and current in order to plan, operate and control the distribution network. Therefore progress in monitoring sensor technology is also needed. Many monitoring sensors for voltage and current of distribution lines have been studied and developed. Almost every type of existing sensor uses a photo device for sensing voltage and current. These are sensitive to leaking resistance of the surface of the sensor case and optical fiber cable for signal transmission. In this paper, we propose a new sensing method for the phase voltage of distribution lines that is robust in terms of the leak resistance of the surface of the case and of the covered wire. A comparison of equivalent circuits between the proposed method and an existing method, the development of the prototype, and the result of a field examination are also described.
This paper reports an output lower property when spot dirt adheres to a small photovoltaic module. It was used the small photovoltaic module of 13W applied to various electric systems. The module consists of 34-cells, cut to 1/4 the silicon single crystal photovoltaic cell of the square whose one side is 103mm. It was found that the photovoltaic output power is reduced by 50% due to a 3% dirt area on the small module. We also showed clearly that the decrease of output power able to improve about 20% by changing photovoltaic cell shape to rectangle.
Global warming is mainly caused by CO2 emission from thermal power plants, which burn fossil fuel with air. One of the countermeasure technologies to prevent the global warming is CO2 recovery from combustion flue gas and the sequestration of CO2 at the underground or in the ocean. SOFC and other fuel cells can produce high concentration CO2, because the reformed fuel gas reacts with oxygen electrochemically without being mixed by air, or diluted by N2. So we propose to operate the multi-staged SOFCs under high utilization of reformed fuel for getting high concentration CO2. In this report, we have estimated the multi-staged SOFCs performance considering H2 diffusion and the combined cycle efficiency of multistage SOFC/gas turbine/CO2 recovery power plant. The power generation efficiency of our CO2 recovery combined cycle is 68.5% and the efficiency of conventional SOFC/GT cycle is 57.8% including the CO2 recovery amine process.
Troubles related to damage of fiber ropes for wiring have sometimes occurred in case of wiring works close to energized transmission lines. Therefore, in order to establish a guideline on the treatment of fiber ropes for wiring works near transmission lines, authors implemented a damage test on the condition of high electric field, then examined the damage characteristics and mechanism. In this paper, mechanism of the dry-band arcing occurring as a result of concentration of voltage across the dry-bands, which are generated by the joule heat caused by the current induced to the wet fiber rope, is shown. In addition, the occurrence condition of the dry-band arcing acquired by the applied voltage test is described.
It is necessary to develop the new power generation system using the unused low temperature thermal energy around 100 degrees C from a viewpoint of global warming prevention. Even if a shape memory alloy is bent in normal temperature, when it is warmed, it has the character which returns to the original straight form. Using this character of a shape memory alloy, unused thermal energy will be able to transform into rotation energy, and finally it can change into electric energy. We solved this energy conversion mechanism and the validity of this theory was indirectly verified by experiment. Furthermore, the power generation characteristic of the Shape Memory Alloy Engine was obtained by experiment.
This paper discusses partial discharge (PD) and breakdown (BD) characteristics of N2O gas and N2O gas mixtures as SF6 substitutes as a function of gas pressure and N2O content for quasi-uniform and non-uniform electric field under lightning impulse and ac voltage application. Experimental results revealed the significant positive synergism in breakdown strength of N2O30%/CO270% and N2O30%/CO250%/O220% gas mixtures under quasi-uniform electric field. Furthermore, corona stabilization effect in N2O30%/CO270% gas mixtures under non-uniform electric field was discussed and suggested to be activated due to the combination of electronegative N2O and CO2 gases.
A simple system for the measurement of transient horizontal electric field along the surface of lossy ground is tested in this paper. The system comprises two vertical conducting probes driven into ground, two series resistors connecting the tops of the two vertical probes, and two voltage probes. Transient horizontal electric field is evaluated as the voltage difference between the tops of the two vertical conducting probes. FDTD simulations show that the transient horizontal electric field evaluated using the measuring system agrees well with that calculated directly in the absence of the system. Furthermore, transient horizontal electric field measured in a small-scale experiment is also in good agreement with the corresponding FDTD-calculated electric field.
Insulation properties of gas mixtures have been actively investigated theoretically by the Boltzmann equation analysis, but they require very detailed data. In this paper, a new simple method is proposed based on swarm parameters. It is applied to representative gas mixtures and shows a rather good performance.