It is expected that future power demand in Japan may decrease because of depopulation. In such case, it may be better to remove some transmission facilities to improve the utilization of remaining transmission network. At the same time, further penetration of renewable generation in the future makes it necessary to reinforce transmission network. Therefore, for the planning of future transmission network, planning method is necessary, which can satisfy simultaneously these requirements of network reduction and network expansion. This paper proposes a novel transmission network planning method considering both the expansion and the reduction of transmission lines. The proposed method utilizes a stochastic planning method to determine the investment and removal of transmission lines. Cost-benefit analysis and robustness evaluation are utilized to evaluate the obtained plans. The effectiveness of the proposed method is shown by a numerical example.
This paper presents a basic study about the control ability of LNG thermal power plant driven by Motor-assisting Gas Turbine (MGT) for frequency stabilization of power grid system. An analytical model of the regulation system with assisting motor and gas turbine is developed, and its performance for frequency stabilization under fluctuating power due to renewable energy sources is investigated by numerical simulation analyses.
Due to the increasing capacity of uncontrollable renewable generators such as photovoltaic power generations, the portion of controllable generators decreases significantly especially in daytime, resulting in the threat of frequency fluctuation exceeding the acceptable range. Implementation of sophisticated power output control method of controllable generators is one of the most practically feasible solutions. This paper proposes a method to load-frequency control (LFC) in consideration of prospected power output response to economic-load dispatching control (EDC). When the prepared LFC capacity is not so sufficient in terms of ramp-rate, the difference between commanded LFC signal and actual power output is accumulated, resulting in unexpected and undesirable power output change later on. The numerical simulation using AGC30 model demonstrates that the proposed method works well by eliminating such an unusable LFC command in consideration of prospected power output response to EDC.
Introduction of renewable energy sources, such as photovoltaic (PV) and wind turbine (WT), might cause supply-and-demand imbalance over a long time. As a countermeasure for supply-and-demand imbalance, wide-area supply-and-demand control considering tie-line between control areas is considered. As the controlled area expands, the number of generators for satisfying ramp-rate and spinning-reserve also increases. Moreover, since a large number of PV and WT are installed over a wide-area, the output of each PV and WT is almost uncorrelated and smoothed by statistical properties. In this paper, a long-term analysis model for determining optimal output while calculating frequency and tie-line power deviation is used for evaluating the wide-area supply-and-demand control. The simulation results reveal that the frequency of power systems and the fuel cost of generators can be decreased by wide-area supply-and-demand control.
When supply-and-demand imbalance occurs due to load fluctuation or output fluctuation of variable renewable energy sources like photovoltaic power generation (PV) in power system, frequency fluctuation occurs. The fluctuation component from a few minutes to 20 minutes period is absorbed by the load frequency control (LFC). When the PV output fluctuation is large, static LFC reserve (e.g. 2% of system capacity) in the conventional operation may be insufficient. If more LFC resereve is secured, the frequency fluctuation may decrease. However, increasing LFC reserve leads to increasing fuel cost because of the output deviation from the most economical operation determined by economic load dispatch. In this paper, a method for securing LFC reserve by using real-time PV output data is proposed. The proposed method decreases LFC reserve in case of the small output fluctuation, while increases LFC reserve in case of the large output fluctuation. The proposed method can solve two problems (i. frequency fluctuation due to LFC reserve shortage, ii. fuel cost increase due to LFC reserve excess) which conventional method (the ratio of LFC reserve to system capacity is constant) cannot solve. With evaluation using IEEJ AGC30 model for automatic generation control analysis, it was shown that the proposed method could decrease the fuel cost compared to the conventional method.
It is important to early predict the out-of-step condition after being subjected to a severe disturbance. A previous study has proposed that the product of the post-disturbance voltage fluctuations and their differentiations (VΔV) is used as the transient stability index in a one-machine power system. This paper presents a theoretical extension from a one-machine to a three-machine power system and the evaluation with a three-machine power system simulation. The algorithm is transparent and does not require machine learning methods, thus would be more acceptable to the industry.
A method is needed to prevent damage of wind power generators from lightning strikes even if lightning strikes the blades. In our experiment, the discharge progressing to the film was hard to penetrate the low surface resistivity polyethylene terephthalate (PET) films with conductive coating on one side, although the discharge always penetrated the uncoated PET film. This result was confirmed when the coated surface of the film was directed to either the high voltage rod electrode side or the ground plate electrode side. It was also confirmed that the progress of negative leader generated from the high voltage rod electrode side was hindered by the film from the photograph with the high speed camera. The time constant was calculated from the product of the surface resistance and the capacitance between the film and the plate electrode. As a result, it was suggested that the propagation of electric potential might be fast because time constant is smaller in the case of the low surface resistivity PET films.
Three dimensional magnetohydrodynamic, two-phase flow and electrochemical reaction coupling numerical simulation of alkaline water electrolysis with magnetic field is conducted to estimate and reveal the mechanism of overvoltage suppression with the magnetic field. The numerical results shown that both vertical magnetic field to the electrode and parallel magnetic field to the electrode suppress the overpotential by the mixing of the electrolyte. This mixing is induced by the secondary flow in both cases. The overvoltage suppression is constantly increased with the increase in magnetic flux density in the case with parallel magnetic field, however, that is saturates in the case with vertical magnetic field to the electrode due to the bubble position is changed by the flow.
The 2011.3.11 large disasters of East Japan's record tremendous Earthquake M9.0·Tsunami etc. have changed conventional sense of electric power energy. This paper describes knowledges obtained through engineering education in about eight years which performed on fourth year late students researching in graduation of electrical/electronic/information engineering department. Review of recent situations of electric power· energy, evaluations and author's opinions are shown.