Sales of electric vehicle are rapidly growing in worldwide. Vehicle grid integration is important for mitigating impact of charging demand on the distribution feeders, realizing renewable powered charging from the rooftop photovoltaic and wind power generation, and contributing to the Vehicle-to-Grid ancillary services for the power systems. This paper reviews current trends of the vehicle grid integration R&D. Future prospective is also pointed out on the key issues such as an electrical interface, multiple services integration, and the electric vehicle living demonstration for open innovation.
The installed capacity of variable renewable generation (VRG) has been rapidly increasing in Japan. Consequently, there is concerned shortage of operating reserve, which compensates demand and supply imbalance. In this study, we analyze the economy of operating reserve by supply-demand simulation in Tohoku area. First, we use historical weather data to calculate forecast and actual output of VRG, and analyze characteristics of prediction errors. Second, we calculate operating cost (fuel cost and start up cost and sodium-sulfur battery cost and Lithium-ion battery cost) by using of unit commitment and economic load dispatch. Finally, operating reserve cost is derived by operating cost, and analyze economic characteristics. As a result, it became clear that operating reserve cost is 1. having different cost for each month 2. depends on fleet of thermal generation on grid and 3. amount of VRG prediction error and characteristic of overprediction/underprediction.
It is necessary to detect a fault point in overhead distribution system for failure restoration. To search the fault point effectively and precisely, we apply TDR (Time Domain Reflectometry) measurement with utility-pole-distance resolution. In this method, we inject a pulse wave into distribution lines and measure the reflection. In this paper, the authors confirm propagation characteristics of overhead distribution system and compare the measurement of the reflected wave with the simulation result. Through the experiments, the authors confirm an influence of parasitic capacitances in overhead distribution facilities such as a transformer and a switchgear. When distribution facility is not connected with distribution line, the reflected wave from every utility pole and the end terminal are observed; the reflected waves from every utility pole are caused by parasitic capacitors between the distribution lines and cross arms. When distribution facility such as a transformer and a switchgear is connected with distribution line, the reflected waves caused by these facilities are observed. As a result, we confirmed that parasitic capacitances of distribution facilities affect the propagation characteristics of distribution failure pulse wave. In addition, the authors developed a simulation tool to evaluate the propagation characteristics of the pulse wave in the overhead distribution system based on the result utilizing the test distribution system, and confirmed that the simulation results corresponded to the measurement results.
Authors have investigated a method to estimate the branch point leading to ground fault location as trunk line between two adjacent distribution lines in case of high resistivity ground fault with voltage gap in distribution line. Ground fault wave form in high resistivity with voltage gap shows often the triangular wave. The terminal points of two adjacent distribution lines need to be connected by common earthing conductor to apply ground fault locating method using common earthing conductor. The branch point up to ground fault location in trunk line between two adjacent distribution lines can be estimated from the time difference of the zero crossover point, where ground fault current flows to grounding electrode of distribution lines via common earthing conductor. This paper clarifies that the origin of the time difference of zero crossover point is related to phase difference of ground fault currents measured at electrodes of two adjacent distribution lines, using by ATP simulation. And this paper mentions field application of distribution line and measurement system of ground fault current flowing to common earthing conductor.
Tohoku Electric Power Co., Inc. is planning to apply polymeric insulators instead of porcelain insulators to improve reliability of 6.6kV distribution lines during heavy contaminated conditions. Distribution lines located in the coastal areas along the Sea of Japan often suffered tracking damage of covered wires from rapid salt contamination resulting in a large-scale power outage. Tracking of covered wires is caused by discharges derived from leakage current flowing on the contaminated insulators surface. To clarify leakage current suppression effect of the polymeric insulators applied for the distribution lines under rapid contaminated condition, salt water pouring tests of model high voltage lines and transformers were carried out using the same types of polymeric insulators. The resulting data confirmed that the polymeric insulators having hydrophobic surface suppress leakage current flowing over the contaminated surface and maintain appropriate insulation performance of the distribution lines.
Surge voltages often have much higher value and changing rate than those of power frequency voltages, and might cause damages to apparatuses or equipment not only on near a surge source, for example lightning struck point, but also on far points from it due to propagating. In addition, surge phenomena often become complex due to the reflections and the superpositions on a point where surge impedances having different value are connected. The surge phenomenon occurring on a power cables connected with a transmission tower is one of these cases. This research's goal is to propose the EMTP model for surge phenomenon occurring on cables arranged through a transmission tower. The proposed model simulates such cable by using a cable model through a pipe conductor. The results calculated by the proposed model ware compared with the results by VSTLrev (Virtual Surge Test Lab. Restructured and Extended Version) which is a surge analysis program based on FDTD (Finite Difference Time Domain) method to verify the accuracy of the proposed model. As a result, the proposed model is reasonable for analysis of a surge phenomenon occurring on a cable through a transmission tower.
In conventional lightning outage rate calculation method of 6.6kV distribution lines, multiphase sparkover is regarded as an outage. On the other hand, observation results have suggested that a lightning outage occasionally may not occur even when multiphase sparkover occurs. In this paper, we proposed a method for evaluating the wire breaking rate due to lightning and estimated the wire breaking rates of the model distribution line.