In a distribution line, power system control and power equipment investment are planned based on a measured power system current. However, recently the mass introduction of PV make it difficult for us to precisely measure the demand curve that is a current consumed by electrical equipment because the reversal power flow from PV systems is superposed. Therefore, the prediction of demand curves of distribution line is indispensable for power system management. Additionally, it is also necessary to estimate the reliability of the predicted values as well as predicted current itself. In this paper, we propose the estimation method of the prediction interval that is the index of reliability based on the past demand curve database. The feature of the proposed method based on Just-In-Time (JIT) modeling make it possible for us to accurately estimate the prediction interval by the normalized database of demand curve. In this paper, some numerical examples are presented, which demonstrate the effectiveness of the proposed method.
Home electric appliances with power electronics devices are increasing. In order to investigate influences due to harmonics currents, grasp of current waveforms for these appliances in low voltage distribution system is important. In this study, estimation technique of electric circuit model for laptops was developed using resistance characteristics of differential voltage (VD).
This paper develops an optimal power generation mix model considering nationwide high-voltage power grid in Japan and aims to analyze the massive deployment of variable renewable (VR) such as PV and wind. The model is developed on the basis of linear programming and includes 200 million constraints and 100 million endogenous variables. The highlight of the model consists in the detailed geographical resolution derived from 135 nodes and 166 high-voltage lines and in the detailed temporal resolution derived from 10 minutes in a whole year. As energy storage technology, the model explicitly incorporates the possible deployment of sodium-sulfur battery and Li-ion battery as well as pumped-storage hydro power plants. Active power flow of the grid is considered through a direct current (DC) method. Simulated results reveal that the considerable deployment of PV and wind does not necessarily require the large-scale installation of rechargeable battery, because the intermittency of PV and wind is controlled by the inter-regional power flow exchange, the flexible operation of ramp generators and pumped-storage hydro and the utilization of VR output curtailments. In Hokkaido area where a large installable potential of wind power is expected, the time interval when a system non-synchronous penetration (SNSP) ratio exhibits more than 50 percent amounts to 1320 hours per annum, implying the requirement of advanced grid operation for the sake of power system security.
This paper proposes a method for the coordinated control of power factor by means of a multi-agent approach. The proposed multi-agent system consists of two types of agent: single feeder agent (F_AG), and bus agent (B_AG). In the proposed system, a F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic generations (PVs).
Electromagnetic transient (EMT) simulations of power systems require accurate representation of models in a wide range of frequencies. This of course applies to the representation of transmission lines, and the phase-domain frequency-dependent line model is often used to this end. The phase-domain line model does not require modal transformation in EMT simulations but requires modal decomposition at its model identification stage, and there are cases where it fails to fix switchovers of propagation modes with respect to frequency. Thus, a frequency-dependent line model which essentially avoids modal decomposition is desired. This paper studies the possibility of a frequency-dependent line model based on the FDTD (Finite Difference Time Domain) method as a candidate which satisfies the above-mentioned requirements. First, improvements regarding computational efficiency and numerical stability are made to Kordi's FDTD-based frequency-dependent line model. Then, the following points are clarified using the developed model: (i) Waveform deformations due to propagation modes with different velocities can be reproduced completely without modal decomposition; (ii) As the time step size becomes larger, waveforms obtained by the developed model become less accurate due to the embedded filter for numerical stability. These points assure, if the error due to the embedded filter is reduced, that the developed model can become a useful frequency-dependent line model without model identification problems.
We proposed two PV output estimation methods. One is using PQ data measured on power system and weather satellite images. Another one is using ΔP and ΔQ which is calculated as amount of unit time change of P and Q. We organized the features of each method and confirmed them in a simulation using the measured data. We will develop new PV output estimation method using advantage of their method, and lift up estimation accuracy.
In markets with high penetration of photovoltaic power, methods to forecasts of solar irradiance one hour ahead of time are expected to provide useful information to execute services of secondary and tertiary regulation of power systems load. The objective of this study is to propose a method to forecast solar irradiance, one hour ahead of time, using numerical weather prediction and recently measured data. The proposed method uses a support vector regression algorithm with a training data selection approach to yield the best possible forecasts for each hour. We verify the validity of the proposed method using it to forecast one year of hourly solar irradiance in local and regional scale for the Kanto region in Japan. For the local forecasts, the method yielded forecast root mean square errors of 0.060 to 0.065kWh/m2 and mean absolute errors ranging from 0.031 to 0.034kWh/m2. These errors were calculated with data from 5h to 20h of each target day. In regional scale, both types of errors were reduced to 0.032kWh/m2 and to 0.019kWh/m2, respectively. Finally, regardless the spatial scale used, the forecasts of the proposed method outperformed considerably reference forecasts based on persistence. Local and regional skills scores varied between 0.67 to 0.73 for the former, and 0.97 for the regional case. These results show indicate the good performance of the proposed method.
This paper has presented a computational fluid dynamics simulation technique for Fault Current Interrupting Arcing Horns (FCIAH) to obtain the pressure and wear mass by an arc in the interruption core. The physical quantities have been calculated spatially and temporally by applying heat source inside the interruption core corresponding to arc power and solving conservation laws step by step taking into account the physical property and ablation. The validity of the simulation technique has been verified by comparing the pressure and wear mass obtained from short-circuit test results.
The characteristics of creeping discharge propagating on the pressboard surface in vegetable-based oils (crude rapeseed oil and PFAE (palm fatty acid ester) oil) and commercial mineral oil with the thermally accelerated aging were investigated by applying AC high voltages of 60Hz to the needle electrode. The pressboard impregnated with the sample oil under the vacuum condition was immersed completely into the same oil, and the tungsten needle electrode was installed in the one side of pressboard surface without the counter electrode. The other side of pressboard has the grounded fine copper rod as a back side electrode (BSE). The discharge shape, streamer extension, streamer velocity, discharge current, discharge energy, pressboard surface tracking and pressboard puncture in the deteriorated oils were examined as a function of the voltage and its imposed time in comparison with those in the original oils. The AC creeping discharge in oils basically grows slowly in the distinctive shape which is characterized by many formations of a fine branching, flashing spot and current pulse under a fixed voltage regardless of the presence/absence of deterioration. However, in this paper, it is reported that the streamer length, streamer velocity, amplitude of discharge current pulses and discharge energy are significantly affected by the deterioration of oils.
The Editorial Committee is working in planning and editing of the publication of Power and Energy Society. In this article, activities of the committee of the last term are reported, and recent trend and future problems are also discussed. The process of planning and editing of the publication, and the challenges to reduce the necessary months for reviewing papers and to increase the number of submitted papers are shown.