The power transformation technology which is the key point of electric power transmission supports our life base in the electric power energy field. Especially, the static apparatus which is used as the electric power conversion and control has an important role at the substation. In this review, the novel development of power transformation technology supporting electric power and energy is described with the maintenance diagnostic technology of sustainability and safety transformer, condenser and its applied technology for variation of power supply and load under the electric power system, high current technology under the power and electric filed and surge analysis technology at the substation. The power transformation technology and static apparatus have been developed in a high level in our country. The problem in this review will be expected to overcome soon.
The technology of an AC circuit breaker in Japan has been progressed aiming for size reduction, high voltage, and high reliability. At the result, the technology of an AC gas circuit breaker in Japan is high-water mark in the world. And, the gas circuit breaker has been adapted as the key component of the gas insulated switchgear and has been used to UHV transmission system. On the other hand recently, it has been needed not only further more high reliability and high cost performance but also adaptability to environment. For an AC gas circuit breaker, it is very important to improve adaptability to environment. In this paper, we observe about forward technology trend and assignment of the AC circuit breaker based on imposed duty and recent technology for the circuit breaker.
Induction motor instead of dc one has been applied widely for dc electric rolling stock because of the advantage of its utility and efficiency. However, further improvement of motor characteristics will be required to realize environment-friendly dc railway system in the future. It is important to study more efficient machine applying dc electric rolling stock for next generation high performance system. On the other hand, the methods to reuse regenerative energy produced by motors effectively are also important. Therefore, we carried out fundamental study on saving energy for electrified railway system. For the first step, we introduced the energy storage system applying electric double-layer capacitors (EDLC), and its control system. And then, we tried to obtain the specification of high temperature superconductor induction/synchronous motor (HTS-ISM), which performance is similar with that of the conventional induction motors. Furthermore, we tried to evaluate an electrified railway system applying energy storage system and HTS-ISM based on simulation. We succeeded in showing the effectiveness of the introductions of energy storage system and HTS-ISM in DC electrified railway system.
Thermal interruption characteristics of SF6 gas circuit breakers were investigated by voltage measurements around current zero. We found that re-ignition peak voltage in the case of an interruption failure could effectively indicate the thermal interruption capability. The efficiency of interruption to puffer pressure could also be evaluated by analyzing the dependency of re-ignition peak voltage on puffer pressure. This technique was applied to experimental design based on the Taguchi method. We successfully optimized the balance of the puffer pressure build-up performance and thermal interruption efficiency to puffer pressure. Finally we demonstrated that a small size research circuit breaker with self-blast interrupter was able to successfully clear the 90% short line fault interruption duty corresponding to 50kA rating in the thermal interruption region.
Optical current transformers (optical CTs) have features that they can be made much smaller and lighter than conventional electromagnetic induction transformers by their simple structure, and contribute to improvement of equipment reliability because of their excellent surge resistance performance. Authors consider optical CTs to be next generation transformers, and are conducting research and development of optical CTs aiming to apply to measuring and protection in electric power systems. Specifically we developed an independent-type optical CT by utilizing basic data of optical CTs accumulated for large current characteristics, temperature characteristics, vibration resistance characteristics, and so on. In performance verification, type tests complying with IEC standards, such as short-time current tests, insulation tests, accuracy tests, and so on, showed good results. This report describes basic principle and configuration of optical CTs. After that, as basic characteristics of optical CTs, conditions and results of verification tests for dielectric breakdown characteristics of sensor fibers, large current characteristics, temperature characteristics, and vibration resistance characteristics are described. Finally, development outline of the independent-type optical CT aiming to apply to all digital substation and its type tests results are described.
An unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.
The PSS (Power System Stabilizer) is a low cost method to stabilize the inter-tie and local oscillations of power network. The PSS's parameters are usually adjusted for the one-machine infinite-bus system model. On the contrary, the real power systems consist of multi machine systems. Then, the PSS parameters coordinated setting considering the real characteristics of the power system network is expected to improve the stability. For this purpose, the MPM (Modal Performance Measure) method is applied for adjusting PSS parameters. The power network mathematical model that is required for this calculation is given by the system identification method. Utilizing the MPM method characteristics, the restrictions such as damping coefficient and maximum gain that are practical design specifications used for conventional controllers, are naturally introduced. Furthermore, RBF (Radial Based Function) frequency weighing is introduced for adjusting frequency responses. The favorable results as expected are obtained by the large scale power system simulations.
This paper presents the development of a new type of voltage regulator that can adequately maintain the voltage supplied to customers, dealing with the problem of voltage control along with the widespread use of photovoltaic power generation systems. The developed equipment is a pole-mounted type voltage regulator consisting of a step-down transformer that converts voltage from high to low and a series transformer for voltage compensation. The demonstration test conducted at the CRIEPI Akagi Test Center confirmed that the voltage control function of the developed voltage regulator is satisfactory based on the proposed control algorism. Also, simulation analysis, on the assumption of the clustered installation of photovoltaic power generation systems, confirmed that the introduction of the developed voltage regulator enables the system voltage to be adequately maintained and full photovoltaic power generation is possible without suppressing the output. It is anticipated that the developed voltage regulator is very effective in adequately regulating the voltage for low voltage distribution systems and gives an effective way for even more widespread photovoltaic power generation.
For the detailed impact assessment of the total power output fluctuation of high penetration photovoltaic power generation system in terms of the load-frequency control, this study evaluated the relationship between the standard deviation (STD) including only shorter cycles than 32 minute and the maximum fluctuation width (MFW) calculated with various window width by using the two data-sets of multi-points observed insolation data. The main results are as follows. The R2 of regression line of STD - MFW correlation diagram is larger than 0.85 for various seasons, while the slope of regression line slightly varies with seasons. The slope of regression line is almost the same for various area sizes during the same season, although the variation ranges of both STD and MFW reduce with larger window width due to a so-called smoothing effect. The results suggest that if the STD of geographical average insolation can be calculated by using stochastic method, the MFW can be calculated with a linear function of STD because of the good correlation between STD and MFW independently of seasons and area sizes.
Based on the past studies regarding the insolation fluctuation, the smoothing effect of insolation among different locations would not be enough for the longer cycle than a few ten minutes. This study evaluated the maximum fluctuation width (MFW) within at most 120 min of ensemble average insolation of 40 points, its clearness index, and ensemble average insolation excluding sun-position dependent component. As the results, when the weather condition became worse after the noon in almost all area, the ensemble average insolation significantly reduced, resulting in MFW of 540W/m2 within 120 min. As other example, when the weather recovered during the morning in many areas, MFW was also large. By using the data observed for 6 months, this study calculated the cumulative frequency distribution of MFW of ensemble average insolation, its clearness index, and ensemble average insolation excluding sun-position dependent component. As the results, the absolute value of MFW of ensemble average insolation calculated with 120 min width window ranges mainly between 200-300W/m2. The absolute value of MWF of insolation excluding sun-position dependent component evaluated with 120 min width window is smaller than 200W/m2 in most days, and is not so different from MWF evaluated with 60 min width window. Finally, this study discussed the practical usability of insolation forecast.
With a rapid increase of renewable energy generation like wind or solar power, the assessment studies of these kinds of generators are so important in order to appraise their positive as well negative effects. So we have been developing a generalized model of wind generator based on an instantaneous value. Through a model based on an instantaneous value is able to simulate detail behavior of the system, it is time consuming to conduct a simulation. So we have adopted a simplified method for frequency converter to our doubly-fed wind generation systems model, and evaluate it under various conditions.
In recent years, electricity markets were organized in many developed countries in the deregulation process of electric power industries. There have been many studies on electricity markets from the viewpoints of economics, mathematics, computer science, etc. Especially, agent-based models of electricity markets have been extensively studied. Meanwhile, many countries promote use of renewable energy for electricity generation. In this paper, we construct and analyze an agent-based model of electricity markets in which wind and photovoltaic power generation firms are introduced. Our results suggest that wind power generation needs to be improved in efficiency to survive in the market, and that bid prices of photovoltaic power generation are rather affected by change of the insolation amount than by change of the total demand.
This paper focuses on residential PV systems in Japan. It projects installation and installed capacity of residential PV systems by analyzing correlation between their pay-back period and annual installation by new and existing houses. Exponential and hyperbolic curves are applied for correlation analysis. But exponential curve shows better fit than hyperbolic one. PV installation in new houses shows stronger correlation with pay-back period than that in existing houses. For the installation projection, target and delayed scenarios are assumed. In the target scenario, target price is achieved as planned. However it is achieved with delay in the delayed scenario. Ongoing subsidy and feed-in-tariff is also assumed. Based on the results of the analysis, the target cumulative installation and installed capacity are achieved in the target scenario. They are not so affected even if without subsidy and feed-in-tariff. But they become almost half in the delayed scenario compared with that in the target scenario. This means system price reduction by R&D and mass production is more effective than ongoing dissemination acceleration programs. To achieve the target capacity, not only cost reduction, but also conversion efficiency improvement by R&D is indispensable.
In arc welding, Gas Tungsten Arc Welding (GTAW) is suitable when good quality and a good surface are required. However, the weld shape is shallow and wide. Furthermore, GTAW welding is slow and inefficient. A deep weld shape is necessary to increase the welding speed. The heat input from the arc and convection flow of the weld pool in formation of weld pool are important. The convection flow varies along with the driving force. Past research has indicated some relation between the driving force and arc characteristics. In this study, the driving force in the weld pool changes with the current density. Flow velocity is simulated, and this relativity is elucidated. The Lorentz force, drag force, and Marangoni effect are focused in driving forces. Consequently, the Lorentz force of the axial direction decreases in direct relation to the -0.60th power of current density near the cathode in the maximum force. This force in the center of the axial direction decreases in relation to the -0.62th power of the current density. In addition, the drag force increases in relation to the 1.70th power of the maximum flow velocity, and the Marangoni effect decreases in direct relation to the -0.20th power of the maximum flow velocity in the maximum force. The driving force is apparently dependent on the arc current density and flow velocity.
Upgraded three-dimensional electromagnetic analysis allows us to calculate the output of the PD-detecting coupler with a dimension of voltage, which can newly propose analytical sensitivity lines for the accurate calibration of partial discharge (PD) instead of experimental ones obtained by the synchronous measurement between UHF method and IEC 60270 standard. Consequently, the fundamental research point out that the actual charge of PD can be estimated from the output of the PD-detecting coupler under regulated conditions of two types of PD sources for the first time since our previous paper was submitted. Introducing the analytical sensitivity line based on the actual charge reveals that the apparent charge obtained by the experimental sensitivity line might be underestimated compared to the actual charge, even if the measurement principle of IEC 60270 is followed. Therefore, the newly-developed calibration technique combined with the actual charge has a significant impact on accurate estimation of the magnitude of PD even from the electromagnetic wave in VHF/UHF/EHF ranges rather than the displacement current based on IEC 60270 standard.
When lightning strikes the tower of a cellular phone base station or other such facilities, power and communication equipments in the vicinity of the tower may suffer extensive damages due to the lightning current flowing backward from the grounding system of the tower. The use of a deeply buried grounding electrode has been proposed recently to suppress such back flow current and a potential rise in the vicinity of the tower. The deeply buried grounding electrode is a bare conductor buried deep in the ground that is connected to a lightning rod on the ground by an insulated wire. When lightning strikes the lightning rod, the lightning current is directed to the electrode from which it diffuses to the ground. The deeply buried grounding electrodes have been installed in cellular phone base stations and other such facilities to solve such problems caused by the back flow current and the potential rise. A grounding mesh is usually laid around such base stations as a grounding system for the facilities on the ground. Therefore, it is important to understand the interactions between the deeply buried grounding electrode and the grounding mesh. In this study, experiments on the interactions between a grounding mesh and a deeply buried grounding electrode have been carried out. Additionally, the transient characteristics of the mesh grounding have researched.
Unit step responses (USRs) of a USR-measuring system recommended by the International Electro-technical Commission (IEC) have been calculated, using the finite-difference time-domain (FDTD) method, for various conditions of grounding and shield ring. The USR measuring system subject to analysis has a resistor divider of height 3.3m and resistance 9kΩ. The conductivity and relative permittivity of the laboratory floor, on which the USR measuring system is placed, are set to a range from σ = 0.001mS/m to ∞ and a range from εr = 1 to 10, respectively. It turns out that USR parameters are not much influenced by either σ or εr if σ is higher than or equal to 10mS/m, and they are close to the USR parameters for σ = ∞. When σ is lower than about 0.1mS/m, USR parameters are more influenced by σ and εr. Variations in the partial response time Tα, the experimental response time Tn, the settling time Ts, and the overshoot β, due to the differences of σ and εr, are 8ns, 14ns, 150ns, and 50%, respectively. Even if the width of horizontal ground metal sheet is extended from wg = 2 to 3m, these variations are not much reduced. The extension of the width of vertical metal sheet from wv = 1 to 2m does not much influence the USR parameters, either. Both the installing height of shield ring h and its diameter d influence the USR parameters: Tα decreases with decreasing h and/or d. Note that the FDTD-calculated USR for σ = 0.1mS/m and εr = 10 agrees reasonably well with the corresponding measured USR: Tα = 19ns, Tn = 6ns, Ts = 310ns, and β = 53% vs. Tα = 16ns, Tn = 10ns, Ts = 280ns, and β = 44%.
Two kinds of innovative measurement method of EDLC's equivalent circuit constants are presented in this paper, “simplified energy method” and “charge-energy method”. The measurement principle of the former method is the same as that of the previously reported “energy method”, but the procedure is much more simplified by employing an analytical approach. In addition to energy, electric charge is incorporated into the latter one to estimate an internal resistance analytically using a simultaneous equation regarding energy and charge. Through the verification with the constant current charge-discharge experiments, we confirmed that both of the proposed measurement methods are concise, highly accurate and reliable.
The widespread use of power electronic devices caused the harmonic pollution in power systems. However, it is difficult to determine customer and utility responsibility for harmonic distortion at the point of common coupling (PCC). In this letter, we propose a method to evaluate harmonic contribution at the PCC using independent component analysis (ICA). This method can evaluate the true harmonic contribution of utility and customer without estimating the harmonic impedance.