This paper presents a new paradigm of power system planning under competitive environment. As the liberalization of power systems become more competitive, power systems are faced with new aspects that the conventional bundled power company has never encountered. The conventional power system planning methods do not match the requirements of competitive environment. In practice, the power system liberalization brings about new environment that puts emphasis on the profit maximization and the risk minimization. Thus, the problem formulation of power system planning should be reformulated to reflect the new aspects in power systems. As the tasks of power system planning, this paper outlines transmission network expansion planning, distribution network expansion planning, and unit commitment under competitive environment. In addition, new tasks such as very short-term load forecasting, electricity price forecasting, and wind power forecasting are described.
The restrictions of transportation are one of the major parameters for transformer design and affect the available capacity, various characteristics and even reliability. With the progress of increasing power demand, transformer size and weight have been increasing. However, in Japan the restrictions for size and weight in rail and road are strict, and several kinds of technology for transformer construction and transportation method have been developed to meet these requirements. One technology is the disassembled transportation method for transformer. Fortunately we have experienced three type disassembled transportation methods for Kamishiiba power station for approximately 50 years. This paper introduces a history on improvement of disassembled transportation technology and development of large power transformer.
In this research, the fundamental premises for deregulation of the electric power industry are reevaluated. The authors develop a simple model to represent wholesale electricity market with highly congested network. The model is developed by simplifying the power system and market in New York ISO based on available data of New York ISO in 2004 with some estimation. Based on the developed model and construction cost data from the past, the economic impact of transmission line addition on market participants and the impact of deregulation on power plant additions under market with transmission congestion are studied. Simulation results show that the market signals may fail to facilitate proper capacity additions and results in the undesirable over-construction and insufficient-construction cycle of capacity addition.
Distribution network has huge number of configuration candidates because the network configuration is determined by state of many sectionalizing switches (opened or closed) installing in terms of keeping power quality, reliability and so on. Since feeder current and voltage depends on the network configuration, distribution loss, voltage imbalance and bank efficiency can be controlled by changing state of these switches. In addition, feeder current and voltage change by out put of distributed generators (DGs) such as photovoltaic generation system, wind turbine generation system and so on, connected to the feeder. Recently, total number of DGs connected to distribution network increases drastically. Therefore, many configuration candidates of the distribution network must be evaluated multiply from various viewpoints such as distribution loss, voltage imbalance, bank efficiency and so on, considering power supply from connected DGs. In this paper, the authors propose a multi-objective optimization method from three evaluation viewpoints ((1) distribution loss, (2) voltage imbalance and (3) bank efficiency) using pareto optimal solution. In the proposed method, after several high-ranking candidates with small distribution loss are extracted by combinatorial optimization method, each candidate are evaluated from the viewpoints of voltage imbalance and bank efficiency using pareto optimal solution, then loss minimum configuration is determined as the best configuration among these solutions. Numerical simulations are carried out for a real scale system model consists of 72 distribution feeders and 234 sectionalizing switches in order to examine the validity of the proposed method.
In this paper, the authors propose a power and heat interchange system using fuel cells (FCs) in a collective housing and develop a determination method of optimal operation schedule for FCs in this system. The developed method is based on tabu search which is one of non-linear optimization methods. In the developed method, the optimal operation schedule is determined by using Pareto optimal solutions from two evaluation viewpoints ((1) running cost, (2) CO2 emission). In order to examine the validity of the developed method, numerical simulations are carried out for the collective housing model with 12 houses in winter, summer and middle season, and the optimal operation schedules are determined.
We have developed an innovative power generation scheduling method using quadratic programming (QP). The advantage of using our method is that it simultaneously solves unit commitment and economic load dispatch. We relax the binary variables of the unit state into continuous variables to apply QP to this problem. We also add the penalty term to converge the value of those variables to 0 or 1 to the objective function; the sum of fuel costs and start-up costs. This penalty term depends on per-unit fuel cost. The possibility of its variable converging to zero increases as the cost increases. This method was applied to a test system of daily generation scheduling that consisted of 29 thermal units, two pumped-storage units, four cascaded-hydro units, and one transmission. The schedule satisfied all constraints, i.e., load-power balance, operation reserve, power flow, minimum up/down-times, and fuel consumption. This result shows that the developed method is effective.
This paper presents a multi-branch exchange method for reconfiguration of distribution systems to reduce their line losses. The method closes and opens several switches simultaneously in each branch exchange operation to expand the search neighborhood. The switches to be closed are selected as the intermediate systems will be meshed configuration. Sequential branch opening method can be applied to open the switches to obtain the radial configuration efficiently. Test examples show the effectiveness of the proposed method in the case of double branch exchange.
Reactive power supply plays an important role in active power supply with adequate system voltages. Various pricing mechanism for reactive power supply have been developed and some of them are adopted in some power systems, however they are in a trial stage. The authors also focus on development of a pricing method for reactive power ancillary services. This problem involves two technical issues: rational estimation of the cost associated with reactive power supply and fair and transparent allocation of the estimated cost among the market participants. This paper proposes methods for evaluating the contribution of generators and demands.
This paper presents a study of the effect of the Interline Power Flow Controller (IPFC) on power oscillation damping and the design process of its damping controller. The power injection model of IPFC suitable for this study is developed in this paper. The damping effect of the PI controller, which is originally for constant power flow control, is evaluated first, and modal analysis of the power system is carried out. Then the pole shifting technique is adopted to stabilize the oscillatory mode having insufficient damping ratio by use of a PSS-type supplementary damping controller. The design process of the supplementary damping controller and the selection of input signal according to the mode observability are presented. Simulation results demonstrate that the IPFC with the above control system is an effective tool to damp power oscillations.
Establishment of an early trouble diagnosis system is demanded to prevent damage of wind turbine generator. Therefore, AE signal occurring by the damage of a wind blade was detected with the AE sensor which installed to the body of wind turbine generator and a pole. In this study, length of a blade of a small wind turbine generator was changed as simulated trouble in the constant wind velocity. The AE signal which occurred at this time was measured with an AE sensor. The signal was processed by FFT analysis, and a change of spectrum strength was examined. Then, trouble diagnosis technology of 50W grade small wind turbine generator was developed. As the results, a method to count the number of times more than threshold of AE signals was suggested by a wave pattern of an AE signal. It was understood that the number of the count was decided as standard to judge normality or abnormality of 50W grade small wind turbine generator.
It is very important to maintain supply reliability under the deregulated environment. The transient stability problem is one of the major concerns in studies of planning and operation of power systems. Nowadays, the time domain simulation is the best available tool for allowing the use of detailed models and for providing reliable results. The main limitations of this approach involve large time of computations. Therefore, this paper proposes a transient stability evaluation method using minimum transient kinetic energy of post-fault trajectories. This method can estimate critical clearing times with only two points of the minimum transient kinetic energy even if the trajectories after a clearing time are stable or unstable. The validity of the proposed method is shown by simulation studies with the IEEJ EAST 10 machine 47 bus system.
The transmission characteristics of the electromagnetic induction type RFID system are greatly influenced by the distance between primary and secondary antenna coils, and the constituted materials. In this paper, the induced current of secondary antenna coil is calculated by the 3-D FEM when both of primary and secondary antenna coils are operated on resonant circuits. As a result, the influences of these analyzed parameters on the transmission characteristics are clarified.
High Temperature Superconducting (HTS) cables have been studied because of low loss and compactness, compared with conventional copper cables. Three-phase cables are usually composed of three single-phase coaxial cables. Recently, a tri-axial cable, composed of three concentric phases, has been intensively developed, because it has advantages such as reduced amount of HTS tapes, small leakage fields and small heat loss in leak, compared with the three single-phase cables. However, there is an inherent imbalance in the three-phase currents in the tri-axial cable due to the differences in radii of the three-phase current layers. The imbalance of the currents causes additional loss and large leakage field in the cable, and deteriorates the electric power quality. Therefore, we propose a new model which is a tri-axial cable composed of two longitudinal sections with different twist pitches to obtain the solutions of the balanced three-phase currents and homogeneous current distribution in each phase of the tri-axial cable. We derive general equation satisfying both the balanced three-phase currents and homogeneous current distribution, as functions of winding pitches, and finally apply it to the simplest cable. We fabricated and tested a 1m long HTS cable in order to verify the proposed theory that satisfies the balanced distribution. The results demonstrate the theory is right. We also investigate the current distributions along the long tri-axial cable considering the capacitances between the layers in the tri-axial cable.