A High Tc Superconducting (HTS) Cable, which has a conductor with superconducting materials discovered in 1986, has been developed since early 1990s. After 10 and several years, the HTS cable has reached to the stage of evaluation at the real grid. Improvement of the performance and progress on the productivity of HTS wires are enhancing opportunities for commercialization of the HTS cable as well as other HTS applications. Especially in the USA, several demonstration projects of the HTS cable are undergoing in order to strengthen the fragile electric power network. In the Albany project, which is one of them, the 3-in-One type HTS cable was installed in 2006 and the world first operation has been conducted with an actual configuration in the long underground duct. In Japan, a new HTS cable project supported by NEDO has just started in order to study operation, maintenance method and related technologies for operating in the actual grid. This paper describes the position of HTS cable in accord with the history of large capacity power cables, summarizes its prospects and technical problems and introduces various projects in the world.
The history in the development of 500kV XLPE cable, especially the struggles in the development work and field application by the engineers has been described in this article. Power cables are one of the large-sized industrial products; however, 500kV XLPE cable requires very sophisticated and fine technologies in its realization. On the way to the goal of its realization, engineers had many struggles against never-experienced subjects and finally they could overcome such difficulties. Field application of 500kV XLPE cable, including installation and jointing, had been established based on the much effort of many engineers.
Discharge noises caused by contaminated insulator string were studied using anechoic room where the difference of the noise waveform due to insulator shape was found. In this study, sound wave propagation of the discharge noises have been simulated using two-dimensional FDTD method to examine the effect of insulator shape on the observed waveform. In the course of the study, the shape data of the insulator was expressed as the set of elements that typify the media (air and solid), directions of air-solid (porcelain) boundary, and directions of ‘Free Space’ boundary by allocating the colors on the corresponding bitmap image file. The source points of the sound were also arranged into the bitmap. Calculated wave propagation for each time step is again expressed in the form of bitmap for visualization. The nature of the calculated sound waveforms for different insulator shapes and discharge positions are compared with that in the experiment.
Distribution systems are inherent monopolies and therefore these have generally been regulated in order to protect customers and to ensure cost-effective operation. In the UK this is one of the functions of OFGEM (Office of Gas and Electricity Markets). Initially the regulation was based on the value of assets but there is a trend nowadays towards performance-based regulation. In order to achieve this, a methodology is needed that enables the reliability performance associated with alternative investment strategies to be compared with the investment cost of these strategies. At present there is no accepted approach for such assessments. Building on the concept of reference networks proposed in Refs. (1), (2), this paper describes how these networks can be used to assess the impact that performance driven investment strategies will have on the improvement in reliability indices. The method has been tested using the underground and overhead part of a real system.
Considering the risk of blackout, Kyushu electric power company has studied about power system restoration at blackout start. Power system at blackout start is so small that over voltage which does not rise in normal power system is able to rise, because of transient phenomena and saturation of transformer which are caused by voltage application. Power system transformers should be applied its voltage as low as possible, ideally from zero, to prevent over-voltage problem. This paper reports field test results of voltage application by a voltage building-up procedure to a 500kV-1000MVA power system transformer through a transmission line.
The photovoltaic (PV) generator changes its power output with the weather. If the PV output changes fast, the power system may require more load-following capability and spinning-reserve. This paper proposes a method of controlling the change rate of the PV output. The PV generator is combined with an electric double layer capacitor (EDLC). The moving average is used to eliminate short period fluctuations of the PV output. The output of the power conversion system (PCS) is determined by the moving average. The output changes within a limited rate. The capacitor voltage is maintained at a constant value to make the capacitor as small as possible. The necessary capacitance is theoretically derived. The effectiveness of this method is verified by the experiment.
In this paper, a structure analysis technique of the core by the magnetostriction was proposed. The magnetic flux density of each element is first calculated by using FEM. Then the magnetostriction of each element is calculated by using the measured result. A magnetostriction is given as initial strain, it changes into the force of each node, and structure analysis is performed. The advantage of giving magnetostriction as initial strain is that it is able to reach force of a point of each element as a vector. Moreover, modal analysis and frequency response analysis were performed. As a result, it was clarified that the resonance was related to the frequency of magnetostriction and natural mode. Then it became possible to forecast the frequency to which core vibrated most. Therefore, proposing analysis technique is very useful.
We have been operated ZnO surge arresters on our power systems since 1970's. But we have been anxious for 1st stage ZnO surge arresters, because these surge arresters have the thermal runaway behavior with the applied continuous operating voltage. I have been examined the resistive leakage currents of ZnO varistors which were enclosed in ZnO surge arresters installed in our substations 20 years ago. I estimated the resistive leakage currents with the long term ageing tests which were repeatedly consisted of supplied AC voltage periods and no voltage periods. As a result, changes of these leakage currents are caused by the migrations of interstitial zinc ions and oxygen ions. On this paper, I describe these ion migrations which are caused by supplied voltages or no supplied voltage and the cracks of depletion layers which could be caused by the migration of oxygen ions.
As clean energy that solves energy resources, many wind turbine generator systems have developed up to now, in Japan. The generation capacity of wind power is above 1 million kW, and the construction also continues from now on. The wind turbine generator systems are built in the good place of the wind condition, and those many are built on the coast of the Japan Sea. However, the coast of the Japan Sea is known as a place with much winter lightning, and wind turbine generator systems also often suffer the damage by winter lightning. The authors observed the lightning current that strikes through the wind turbine generator systems directly, in order to establish on the lightning protection of them. The authors acquired dozens of data as a result of observation in Akita Japan for 17 months. Based on these data, some considerations were performed about the performance of winter lightning that struck through the wind turbine generator systems. As the result of consideration, we found some interesting knowledge following sentence. It made clear anew that the tower which is a place of high position from the ground and on the windward has much number of lightning flash and many total flash charges. The lightning stroke current divided the tower pipe and ground leads. About 70% of the observed lightning current flowed to the tower pipe, and about 30% is divided into two grounding leads connected to the leg of tower. All of steep current that is on a wave front flow a tower side, it dose not flow to a grounding leads side. The distributions of lightning parameters between our observation results and past one are in good conformity.
Periodical inspections are normally made on indoor low-voltage distribution circuits once every four years in Japan in compliance with the Electricity Utilities Industry Law. Switching of circuit breakers in distribution panels is necessary to verify electrical safety of indoor low-voltage distribution circuits. Items tested include insulation resistance. Failure of household electrical appliances during the switching operation of circuit breakers is very rare. The main cause is considered to be switching surges. However, the reason and mechanism of failures have not been clarified. We conducted an investigation into actual conditions of switching surges in indoor low-voltage distribution systems. This paper presents the investigation results.
Insulation diagnosis is vital issue for safety of urban lives despite of the difficulty of power interruption even for the diagnosis. Recently, live-line insulation diagnosis becomes more important and realistic to maintain good insulation conditions of power lines in apartment houses in wide range of residential sizes. This paper describes new trend of insulation diagnosis of power lines of apartment houses based on clip-on current measurement method with a lot of live-line measurement data and also describes the applicability of new live-line insulation diagnostic method.