Power system analysis is essential for efficient and reliable power system operation and control. Recently, online security assessment system has become of importance, as more efficient use of power networks is eagerly required. In this article, fast power system analysis techniques such as contingency screening, parallel processing and intelligent systems application are briefly surveyed from the view point of their application to online dynamic security assessment.
Since the first prototype GIS was constructed in Japan in 1968, rapid progress and wide extension were made during a few years. In 1973, the first 550kV hybrid GIS was constructed and after three years, in 1976, the world first 550kV full GIS was completed in Ohi nuclear power plant. During this remarkable short period of GIS development, effort of utilities and Mitsubishi Electric Corporation, as a manufacturer, are mentioned. Especially, some of technical subjects to the large sized equipments were picked up and that solutions were reported to be correct judging from up-to-date knowledges.
Accurate estimation of the lightning striking points is practically important to find the fault location of the power line. Recent progress of the lightning locating technique has made it possible to estimate the striking points with the accuracy of less than 1km. To enhance the location accuracy, the authors measure the vertical electric field at six points around Shirakawa area in Fukushima prefecture. The distance between measuring points is about 10km, which is less than one tenth of the distance of the direction finders (DF) of the lightning location system. In this paper, the authors estimated the location of the lightning striking points by using the time of arrival technique and compared with the results obtained by the lightning location system. Furthermore, the cause of the discrepancy between estimated lightning striking points is discussed, and the location accuracy by the authors' method is evaluated.
This paper proposes a new approach for disconnection control of wind power generators to reduce the frequency fluctuation caused by wind power. The approach is based on the correlation between frequency and total output of wind power generators and the turbulence degrees of individual wind power generators. At a control center, frequency and all the outputs of wind power generators are monitored, and the correlation and the turbulence degrees are computed on-line. If the large variation of frequency is detected, then whether the variation comes from the wind power generators or loads is checked by using the correlation. When the wind power generators cause the frequency variation, the wind power generator with maximum turbulence degree is searched and disconnected from the power systems. This search and disconnection process is repeated until the correlation reaches the level where the frequency variation observed is not caused by the wind power generators. The effectiveness of the proposed approach was confirmed with the simulation studies of a two-area interconnected power system including a lot of wind power generators. The results show that the correlation and the turbulence degree are useful for the reduction of frequency fluctuation so as not to disconnect too many wind power generators.
With the rationalization of specifications, a gas-insulated switchgear (GIS) has been miniaturized in recent years. GIS for AC is designed so that it can resist an AC test voltage and lightning impulse (LI) test voltage. However, a test is not made for the residual DC voltage occurring in an AC GIS spacer when switchgear operates. The residual DC voltage is also not sufficiently investigated in this case. In the DC electric field, the electrified charge strengthens the creeping electric field (Et) of an insulator. The withstand performance of an insulating spacer to DC depends on the maximum creeping electric field (Etmax). When the volume resistivity in the surface layer of an insulating spacer is non-uniform, Et is strengthened at the non-uniform point and the corresponding point usually becomes Etmax. In this paper, the change in Etmax was investigated from experimental results and analysis when a point at which volume resistivity is non-uniform exists in the surface layer of an insulating spacer. Moreover, creeping flashover characteristics were also investigated and evaluated when a LI voltage is superimposed and applied on and to the residual DC voltage.
In this paper we analyze electric load data using Independent Component Analysis (ICA) approach. ICA is a method for finding unknown signals from observed ones. Given that observations are linear mixture of independent signal sources, then we can estimate signal sources from just only observations using ICA method. There are some papers studying time-series data with ICA. They apply ICA to economic data, climate data and topic identification. One of the advantages of using ICA is its ability to capture data structures. Among many ICA algorithms, we adopt Complexity Pursuit (CP). CP is based on maximizing nongaussianity and temporal structure of signals. We aim at finding underlying structure of electric load in Kansai Electric Power Co., Inc. As a result, 13 components are extracted from 2004 to 2006 data. Then we explore the meanings of components, and separate weeks based on each component's fluctuation. The groups are related to each season.
In this paper, we have proposed that an electric double layer capacitor storage, which has quick response in output or input of electricity but has smaller capacity than normal secondary batteries, is applied to a residential fuel cell co-generation system to shave spike-like electric power consumptions. The method is expected to enhance the utilization rate of the system and to moderate burdens for power grid connecting to such distributed generator as fuel cell. A low-pass filter method was introduced for balancing between the power supply and the demand, and leveling the power input from a grid. According to the simulation by using practically measured load patterns, the appropriate storage capacity is about 500Wh for a household, the fuel cell utilization rate or the grid burden improvement is increased by around 40% in comparison with the case of the system without storage capacity. It has been clarified that, in the energy network method of over 5 households, the storage capacity can be approximately reduced down to 40% with extreme burden improvement less than 90% of the stand alone condition. Also we have verified the practical operation and the performance by using an experimental system.
The situation in which the plan of a new distribution network system should be examined as an electric power company approaches by the multi-machine interconnection of the distributed generators that will be expected in the near future. Then, the authors assumed applying the distribution system which may be adopted as the near future to a system and equipment of the Kansai Electric Power Company, and executed the reliability evaluation concerning the outage energy and voltage sag power that used the real scale model of distribution system by the stochastic reliability evaluation that used the Monte Carlo method.
High DG penetration will seriously spoil short-term voltage stability of load in bulk power system. Simulation results on previous studies by the authors have shown that dynamic voltage support (DVS) capability of DG improves the stability, but experimental evaluation doesn't exist yet. This paper presents the effect of DVS capability of DG on an experimental circuit, which consists of an induction motor, a resistance load, and a compensation capacitor behind a reactance. First, an experimental set up that causes voltage instability without DVS is made up. Second, an improvement in DG inverter control is made to realize low voltage ride-through (LVRT) capability and DVS capability, and the DG's performance is confirmed by voltage sag tests. Finally, the tests on the experimental set up demonstrate that DVS capability improves greatly short-term voltage stability of power system loads, and the experimental results give good agreement with simulation results.
Connecting Distributed Generations (DGs) into distribution system has presented challenge of controlling voltage profile in distribution system. The presence of DGs makes voltage profile non-uniform and may result in large voltage fluctuation and over-voltage at loads. Therefore, there is need for strict limitation on power injected by DGs. This paper proposes an effective method to overcome the problem of increase/decrease of voltage in distribution system due to the presence of DGs, and it also realizes higher permissible power injected by DGs. In the proposed method, the configuration of distribution system is changed, firstly, from radial to loop type by tying the receiving ends of feeders. Secondly, a series type Back-To-Back (BTB) converter is installed near substation to improve voltage profile by controlling the voltages of the two nodes in the looped feeders. The effectiveness of the proposed method for improvement of the voltage profile and reduction of the converter capacity is presented.
The high-speed vacuum circuit breaker, which forced the fault current to zero was investigated. The test circuit breaker consisted of a vacuum interrupter and a high frequency current source. The vacuum interrupter, which had the axial magnetic field electrode and the disk shape electrode, was tested. The arcing period of the high-speed vacuum circuit breaker is much shorter than that of conventional circuit breaker. The arc behavior of the test electrodes immediately after the contact separation was observed by a high-speed video camcorder. The relation between the current waveform just before the current zero and the interruption ability by varying the high frequency current source was investigated experimentally. The results demonstrate the interruption ability and the arc behavior of the high-speed vacuum circuit breaker. The high current interruption was made possible by the low current period just before the current zero, although the arcing time is short and the arc is concentrated.
In this technical note, recently proposed engineering models of the lightning return stroke and their application to lightning electromagnetic pulse calculations are reviewed and evaluated. In Section 2, the transmission line model and the traveling current source model, which have been used most frequently out of engineering models of the lightning return stroke attached to flat ground, are described. Then, two models, which have been proposed recently and can reproduce all of five features observed in typical measured lightning electromagnetic field waveforms at different distances from a lightning channel, are explained. In Section 3, two models for the lightning return stroke attached to a tall grounded object are reviewed. One is the distributed shunt current source model, and the other is the lumped series voltage source model. In Section 4, expressions for calculating electric and magnetic fields radiated from a lightning return stroke channel (and a tall strike object if present), from the current distribution along the lightning channel given by an engineering return stroke model, are shown. Three different expressions for electric field are shown here. The first one is a most widely used expression derived using Lorentz condition, the second one is an expression derived recently using the continuity equation, and the last one is an expression valid only in the restricted condition that the return stroke wavefront speed is equal to the speed of light and a return stroke current wave propagates without attenuation or dispersion. In Section 5, new findings obtained from electromagnetic calculations using the engineering models for the lightning return stroke attached to a tall object are shown. For example, the vertical electric field in the vicinity of a tall strike object is reduced significantly by the presence of the tall object, while remote electric and magnetic fields are enhanced by it.