In this paper, the impacts on cascading failures by the configuration of the power systems are presented. The object systems consist of four unit network models, and each unit network model is connected by four different types of interconnection configuration. Two different unit network models—mesh and radial—are considered. Cascading failures are simulated under the various system models and Averaged Expected Power Not Supplied (AEPNS) is computed, which is used as an index of power system reliability. The differences of the AEPNS by the methods for correcting supply-demand imbalance are compared. The results of analysis indicate that network configuration and methods for correcting supply-demand imbalance could affect power system reliability.
When the ground fault by the contact between high and low voltage lines occurs, the line ground current flows into the earth resistance in the secondary side of the pole transformer. So the ground voltage rises from 300 to 600V, it is necessary to open the electric circuit within 1 second for safety. The methods to detect the ground fault are classified into “direct detection” and “indirect detection”. Previously, the direct detection is to detect the zero phase voltage by the over voltage ground relay from high voltage distribution line side. In this paper, we propose a new method to detect the ground fault directly from low voltage distribution line side for three phase power conditioners. During the ground fault, line currents are three phase unbalanced currents, and make the unbalance of the line voltage changes through the line impedance. Proposed method detects the unbalance of the line voltage changes from the view point of both the scalar change and the vector change. Firstly, we describe the detection principle by using the simple high voltage distribution line model. Next, we have developed the analysis model for three phase unbalanced power flow in considering the influence of various power system conditions, and clarified the detection setting values for the proposed method.
Basic algorithm for equitable distribution of wind power curtailment has been developed. The algorithm based on wind power forecasts and mathematical programming consists of four major phases: annual curtailment plan, plan for the next day, plan for the current day and revisions of annual plan. The validity of the algorithm has been demonstrated by simulations.
In this paper, a hybrid model of fuzzy clustering and ANN (Artificial Neural Network) is proposed for electricity price forecasting. Due to the complicated behavior of electricity price in power markets, markets players are interested in maximizing profits while minimizing risks. As a result, more accurate models are required to deal with electricity price forecasting. This paper proposes a new method that makes use of fuzzy clustering preconditioned GRBFN (Generalized Radial Basis Function Network) to provide more accurate predicted prices. Fuzzy clustering plays a key role to prevent the number of learning data from decreasing at each cluster. GRBFN is one of efficient ANNs to approximate nonlinear systems. Furthermore, a modified GRBFN model is developed to improve the performance of GRBFN with the use of DA (Deterministic Annealing) clustering for the parameters initialization and EPSO (Evolutionary Particle Swarm Optimization) for optimizing the parameters of GRBFN. The proposed method is successfully applied to real data of ISO New England, USA.
Owing to high demand for electromagnetic transient (EMT) simulations of power systems, faster simulations are desired for EMT analysis programs since the circuits simulated are becoming increasingly large and complex. In this paper, we describe solution process parallelization for an EMT analysis program executed on a general-purpose PC with a multi-core processor. If the number of subsystems is greater than the number of available cores, an appropriate task-scheduling algorithm for efficient load balancing is required. Accordingly, we discuss the effect of task-scheduling algorithms on the computation time through a verification using static and dynamic scheduling algorithms. Finally, it is shown that parallel computation of the solution process with six threads in this study achieves over three times faster computation than the conventional sequential computation.
From growing interests in the environment issues, promotion of photovoltaic power generation (PV) is accelerated in the world. Meanwhile, rapid chargers (RCs) for popularized electric vehicles are being installed in urban areas. These two trends in distribution system might cause severer voltage fluctuation problems. On the other hand, a RC can provide the reactive power support, which is capable of voltage regulation. Based on this viewpoint, this paper proposes a new framework of voltage regulation, in which the reactive power compensation by RCs is actively utilized. The proposed voltage regulation method combines two different control functions with consideration for over-compensation avoidance. This paper ascertains the validity of proposed voltage regulation method through numerical simulations.
This paper presents parallel multi-population differential evolutionary particle swarm optimization (DEEPSO) for voltage and reactive power control (VQC). The problem can be formulated as a mixed integer nonlinear optimization problem and various evolutionary computation techniques have been applied to the problem including PSO, differential evolution (DE), and DEEPSO. Since VQC is one of the on-line controls, speed-up of computation is required. Moreover, there is still room for improvement in solution quality. This paper applies parallel multi-population DEEPSO in order to speed up the calculation and improve solution quality. The proposed method is applied to IEEE 30, 57 and 118 bus systems. The results indicate that the proposed method can realize fast computation and minimize more active power losses than the conventional evolutionary computation techniques.
In this paper, a new method is proposed for the optimal allocation of PMUs (Phasor Measurement Units) in power system state estimation. They play an important role to provide more accurate measurements with state estimation. In practice, it is of main concern how to optimize the allocation for a set of power system conditions. The proposed method makes use of EPSO (Evolutionary Particle Swarm Optimization) to determine the optimal allocation of PMUs from a standpoint of estimates accuracy. In practice, the optimal allocation is dependent upon the power system conditions. To overcome the problem, this paper introduces MCS (Monte Carlo Simulation) in consideration of the nodal correlation. Specifically, the moment matching method is used to evaluate the optimal allocation efficiently. The effectiveness of the proposed method is demonstrated in the IEEE 30-node power system.
In recent years, it is concerned that rapid introduction of residential photovoltaic generation system (PVs) may cause voltage unbalance in high voltage distribution system. Load Ratio control Transformer (LRT) at substation and Step Voltage Regulator (SVR) are used for voltage regulation, however, unbalanced voltage make SVR and LRT difficult to regulate the line voltage. The authors have studied on voltage unbalance suppression system using single phase static capacitors (named SC system), and presented the control method for regulating the line voltage in proper range suppressing the unbalanced voltage. However, the input pattern of SCs is restricted due to the voltage rise caused by PVs. In order to solve this problem, cooperative control in SVR is required to expand the working range of SC system for suppressing voltage unbalance. In this paper, the authors propose the method of determination of a target voltage of SVR for cooperative control with SC system in distribution line connected large amount of PVs. The proposed method is verified by simulation study on distribution system model and the impact on amount of PV is discussed by suppressing unbalanced voltage using SC system.
Toward low carbon society, renewable energy is expected to play the major role in mitigating carbon emission from power sector, however, with significant amount and share of grid connected variable renewable energy (VRE), namely PV and wind, balance between necessary balancing capacity and available balancing capacity must be always properly maintained. This paper presents an analysis how the power system and market will be changed, taking the Japanese power system in 2030, focusing on the consequence of balancing capability interchange through interconnection using marginal cost based on the newly developed demand-supply analysis model.
Although renewable energies such as photovoltaics are penetrating rapidly, in order to harness their varying output efficiently and robustly it is necessary to control the power systems with not only hardware facilities but also software systems. To this end, electricity storage devices from large stationary batteries to electric vehicles will be one of the most important hardware systems, which will require also scheduled operation based on forecasting output of renewables. As the forecast of renewables' output is a complex problem because of its large and varying uncertainty, a probabilistic forecast is better than a deterministic forecast. The aim of this paper is to advance a novel approach of probabilistic forecast of solar irradiation with consideration of temporal correlation as well as varying uncertainty by using copula-based Markov process and variable dispersion beta regression. Employing these methods, we have verified in terms of the performance indexes of reliability and sharpness that the marginal distributions of solar irradiations are well expressed by the beta distribution with varying dispersion as well as their temporal correlation can be well modeled by using Gumbel copula. This temporally-correlated model enables updating a day-ahead forecast by observed irradiations resulting in improving confidence intervals. In addition, probabilistic scenarios of irradiations can be generated by this model, which enables a precise probabilistic forecast of daily cumulative irradiation.
Tank vibration of loaded transformer was measured by 3-axis acceleration sensors to diagnose the abnormal and degraded conditions. Although there have been calculated and reported the natural vibration characteristics of transformer core and windings, the attempts to detect these natural vibrations on the tank were few. These natural vibration characteristics represent the conditions of core and windings.
From this point of view, this paper describes what types of tank vibration may occur and how to detect the natural vibrations of core and windings. The measurement data are classified into 3 categories and we can distinguish the difference between small mechanical vibration and other vibration.
This paper presents the development results of a -1MV DC filter and DC measurement systems for an ITER neutral beam injector system. High accuracy of 0.5% and fast responsivity of 3.3µs, -3dB are required for the DC measurement systems: both DC voltage dividers and DCCTs. Circuit design and thermal flow design were carried out to clarify and minimize their effects on the accuracy and responsivity. The validity of the established design was demonstrated by the actual-product tests; temperature rise of each components fell below the allowable value; inner components of DC filter withstood DC -1.2MV; each voltage divider accurately measured the voltage during the DC -1.2MV withstand voltage test; the voltage dividers and the DCCTs were adequate to the requirements of responsivity (3.3µs, -3dB).
This paper presents an evaluation of economical capacity of storage batteries equipped with residential PV systems. In around 2019, many of power companies' ten-year contracts with PV system owners will come to expire, pushing down the selling price of PV generated energy. This, if combined with a declining battery price, would make it more economical to self-consume PV generated energy than selling the electricity to the utilities. The authors explore the optimized storage battery capacity and charge-discharge pattern by using load and PV output data of 200 houses, and by linear programming. Results show 5.8kWh battery is suitable for an average house with 4.5kW PV system when the battery system price is about ¥60,000/kWh. The authors analyze the daily storage start timing's impact on reverse power which affects power system operation, the optimum combination of PV and battery capacity, and each house's deciding factors for optimum storage capacity and so on.
When a transformer is energized, inrush currents whose magnitudes may reach tens of its nominal current occur. Since the inrush currents lead to a voltage drop, this may cause stops and malfunctions of electrical appliances. In addition, the over-currents may cause an unnecessary operation of an over-current relay and affect the power quality of the distribution system. Currently, distribution system operators use current-versus-time curves of transformer inrush currents for the studies of such phenomena. However, the studies based on the current-versus-time curve give approximate results, and studies based on the current-versus-flux curve is required so as to obtain accurate results. Considering this point, this report proposes a method to convert a given current-versus-time curve to a current-versus-flux one for the case of single-phase transformers. Using the current-versus-flux curve obtained, detailed simulations can be performed using an electromagnetic transient analysis program such as XTAP. In this report, the proposed method is validated by experimental results using a single-phase transformer.
A large scale battery energy storage system, which can output power at MW-order, has many Power Conditioning Systems (PCSs). The authors have proposed an active power distribution method for PCS. The active power distribution method uses information of Need of Charge (NOC) and Maximum Efficiency Power point (MEP), and the method is called NOC-MEP method. The NOC-MEP method showed higher charge/discharge efficiency than the conventional method in which active power is equally distributed to each PCS. The NOC-MEP method has been installed in the battery system at Nishi-Sendai substation of Tohoku Electric Power Co. Inc. This paper reports the charge/discharge efficiency of battery system at Nishi-Sendai substation, which uses the NOC-MEP method.
The 28th Power and Energy Society Annual Conference was held on September 5-7, 2017 at Meiji University Nakano Campus in Tokyo. The total number of technical papers was 386, and technical sessions were 49 (48 oral sessions and 1 poster session). An invited speech, a panel discussion and a special lecture were also organized in the conference period while forum and tutorial sessions were newly held on September 4. The all events were very well attended and the final enrollment attained to 1026 registrations. The conference was successfully closed by the great contribution of all participants. The outline of the conference is reported in this article.