The article reviews recent technology trend in power cables used for transmission in oversea. Especially, this article deals with the power transmission cable system feature and technology including typical main construction projects of underground and submarine power cables in America, Europe, and Asian countries. The review puts emphasis on the subjects of transmission power capacity calculation, cable types, cable joint, cable and joint design in installation and construction, cable quality evaluation test, field test method and maintenance and aging diagnosis methods as well as recent main oversea standards in comparison with those in Japan.
The diffusion of the dispersed power generation systems has been expected against the global environmental issue, the resources problem, and the energy security. The dispersed generators for residential use are connected to the low voltage distribution line, which can cause three-phase unbalance in the middle voltage distribution line. The three-phase unbalance leads to less performance of the grid system and inefficient operation of the three-phase electrical equipment. In the AC traction system, Scott-transformer, which has a simple configuration and can suppress three-phase unbalance caused by the single phase loads, has been used for three-phase unbalance compensation. In the previous study, the simulation results showed that the Scott-transformer could reduce the three-phase unbalance in the distribution system with dispersed generators. In the simulation, the dispersed generators were given as an ideal current source with a fixed amplitude and a phase angle. In this study, the current source feeds an AC current synchronized with the grid voltage at the connection point with power factor 1.0, and adjusts the amplitude to supply a constant output power. The effects of Scott-transformer for three-phase unbalance have been confirmed in the simulation as well as the previous study.
This paper proposes a novel control method considering both transient stability and voltage stability to be applied to online stabilizing control system of a long-distance transmission system. Power system in the future with a large amount of renewable energy sources may be vulnerable to transient instability and/or voltage instability because of balance stop of synchronous units to avoid power surplus. The proposed method analyzes successively both transient stability and voltage stability after a severe disturbance to assure transient stability and voltage stability simultaneously. This feature is realized by taking advantage of the difference of time domains of the two analyses. Numerical examples using IEEJ WEST 30 standard system show the effectiveness of the proposed method.
Japanese electric power utilities installed many electric power facilities for the increasing power demand in the high economic growth era. However these facilities have aged about 40 years and they should be replaced in the near future. The utilities will have to replace the facilities more than now at the same time because of the increase of the power facility replaces. Therefore the outage planning should take place more efficiently. However, to make the outage plan, it requires time and labor. Because the outage plan must determine (1) Outage schedule, (2) Power system configuration during outage works and (3) System switching of the power system in order to conduct the outage works. To solve these problems, a fast outage planning method focusing on circuit breakers near the outage facilities is proposed in this paper. Finally, simulations are run using the IEEJ sub-transmission system model I to confirm the validity of the proposed method.
Japan plans to introduce a large amount of photovoltaic (PV) power generation capacity. In this paper, we focus on voltage and reactive power in large-scale PV systems. First, we propose a two-layered shunt capacitor (SC) scheduling method using multi objective particle swarm optimization (MOPSO) and dynamic programming (DP). By using MOPSO, cost efficiency and reliability in power system planning and operation can be more accurately analyzed, and by using DP, switching times can be assessed. We then propose an effective static var compensator (SVC) control method for use in situations where PV outputs fluctuate sharply over short time intervals in order to control reactive power flows caused by changing PV output, and we also consider efficiency of SC and transformer LTC. Based on simulations run on a modified Ward-Hale 6-bus system to verify the validity of the method, we can confirm that its capability over a normal voltage range for controlling power systems with a large degree of penetration.
This paper focuses on residential PV systems in Japan and analyzes their factors of dissemination quantitatively over the years by new and existing houses using annual prefectural data. A method is proposed based on regression analysis and analysis of factors using results of the regression analysis. The regression analysis is applied annually to the correlation between payback period and annual installation rate in the 47 prefectures by new and existing houses. By using the estimated annual regression lines, annual increment of installation rate is separated into two parts. One is effect of economic factors, which can be calculated with regression line for the prior year and payback period in the current year, and the rest is effect of non-economic factors. Based on the results of the analysis, non-economic effects were dominant in the early years especially for existing houses. However, recently the economic effects have become dominant in both new and existing houses. From FY2001 to FY2003, factors of dissemination are different in new and existing houses reflecting housing market. Non-economic factors are mainly based on high environment consciousness and many other occasional factors, such as the booming due to a subsidy and Feed-in-Tariff, sales promotion by house and PV cell manufacturers.
The number of forward contracts traded in Japan Electric Power Exchange (JEPX) is desired to increase. However, few studies have clarified what factors have contributed to impacting the number of forward contracts traded. In this study, the authors analyzed the number of forward contracts using four kinds of count regression models. As a result, negative binomial regression model and zero-inflated models were able to better express the expected counts, by incorporating the overdispersion and excess zeros present in the observed data. Among others, the spot market can carry positive influences on the expected counts, by about 12% for 1 yen/kWh increase in price, and by about 27% for 0.1%-point increase in volumes. The zero-inflated models revealed that as many as three fourth of the entire forward products have high probability of zero counts, while the rest one fourth may see an increased number of counts as the spot market price and/or the spot volume become higher.
Photovoltaic generation is eco-friendly to utilize solar energy. The photovoltaic power systems have become widely used as clean energy power plants which are constructed on small spaces such as roofs of general houses and buildings. Due to such particular installation locations that there is almost no interrupter for direct lightning strokes and electromagnetic waves radiated from lightning, the number of malfunctions and breakdowns caused by the direct or induced lightning may increase. In this study, overvoltages generated by a lightning strike to a frame of a photovoltaic array are measured at an actual power plant. As a result, it is confirmed that the overvoltage between a power line and the ground has been caused by grounding potential rise of the photovoltaic power system, and that between two DC power lines has been caused by electrostatic and electromagnetic inductions. From those results, the levels of overvoltages are discussed.
The corrosion behavior of aluminum wire which is galvanically coupled with copper in 5mass% NaCl solution was studied by surface observation and polarization curve measurements. The corrosion rate of the aluminum and copper coupled specimen was estimated by using polarization resistance method and it is about 0.03mAcm-2 which is roughly correspondent with the limiting diffusion current density of dissolved oxygen in the NaCl solution. It is shown and considered that morphological characteristics of the galvanic corrosion of aluminum wire specimen showed deep but narrow mouth of pitting cavities.
This letter presents a new method for calculating frequency and voltage fluctuations of power system with wind generators installed. The new method is based on the transfer function models for frequency and voltage responses, from which voltage response of each node in the power system as well as the frequency response can be obtained easily and quickly.