Minoru Kitagawa

Implementation of genetic algorithm for distribution systems loss minimum re-configuration

The loss minimum reconfiguration problem in the open loop radial distribution system is basically one of complex combinatorial optimization, since the normal open sectionalizing switches must be determined appropriately. The genetic algorithm was successfully applied to the loss minimum reconfiguration problem. In the proposed algorithm, strings consist of sectionalizing switch status or radial configurations, and the fitness function consists of the total system losses and penalty value of voltage drop and current capacity violations. The loss minimum reconfiguration problem is formulated as a mixed integer programming problem. The essential components of the genetic algorithm are briefly described. A detailed solution methodology by the use of genetic algorithm is outlined. Numerical examples demonstrate the validity and effectiveness of the proposed methodology. >

New approximate optimization method for distribution system planning

An algorithm to obtain an approximate optimal solution to the problem of large-scale radial distribution system planning is proposed. The distribution planning problem is formulated as a MIP (mixed integer programming) problem. The set of constraints is reduced to a set of continuous variable linear equations by using the fact that the basis of the simplex tableau consists of the power flow variables of radial branch. This linear problem is solved by pivot operations which correspond to a branch-exchange of the radial network. Numerical examples are presented to demonstrate the validity and effectiveness of the algorithm. >

Multi-year expansion planning for distribution systems

A multi-term distribution system expansion planning method is proposed. Many mathematical programming approaches have been proposed in this area. However, because of the complexity of the problem or the limitations of a computational time and memory size, these methods can only be applied to a small-scale system. To solve large-scale problems, the authors propose a new decomposition algorithm based on the branch exchange method. A n-years planning problem is decomposed into n one-year planning problems, and one-year results are coordinated through what can be called the forward/backward path. The validity and effectiveness of the algorithm are ascertained by applying it to real-scale numerical examples. >

An investigation of voltage instability problems

The authors investigate the voltage stability problem based on singular perturbation theory. Possible voltage instability patterns are classified into four types (I, II-1, II-2S, and II-2D) according to the mechanism causing voltage instability. Several features of each type of instability are studied as well as their analysis methods. Voltage instability tends to begin with type I and then leads to one of the remaining types. The load flow Jacobian can be an effective index to approximately assess type I and II-2S instabilities, while types II-1 and II-2D require direct nonlinear analyses and eigenvalue analyses, respectively. The validity of the classification proposed has been verified through numerical simulations and theoretical analyses which take into account dynamic characteristics of generating units, loads, and tap-changing transformers. >

Distribution systems expansion planning by multi-stage branch exchange

The authors present a multistage branch exchange algorithm for solving expansion planning problems in distribution systems. Since it is formulated as a combinatorial optimization problem, it is difficult to solve such a large-scale problem accurately. Therefore, in order to find a solution quickly, the authors have developed a method based on the branch exchange technique which is able to find an approximate solution. To obtain a more accurate solution, the multistage branch exchange algorithm is introduced. The validity and effectiveness of the proposed algorithm are demonstrated by applying it to a 59-node, 69-branch numerical example system. >

Interaction among multiple controls in tap change under load transformers

This paper investigates the dynamic behaviour of tap changing operations in tap change under load (TCUL) transformers. Interactions among multiple TCUL controls cause oscillatory behaviour in tap changing actions, which unnecessarily increases tap operations before they reach equilibrium. Sufficient conditions for stability are derived and features of the phenomena are examined through theoretical analysis as well as through numerical simulation.

Algorithm for expansion planning in distribution systems taking faults into consideration

This paper presents a solution algorithm for expansion planning in distribution systems in which fault cases are taken into consideration. The proposed method can take all the predetermined severe fault cases into consideration simultaneously, and can avoid installing excess facilities without affecting the ability for fault restoration. In the algorithm, the whole problem is decomposed into sub-problems according to pre-determined fault cases, and is efficiently solved by using the branch exchange algorithm and the decomposition-coordination technique. The validity and the effectiveness of the proposed algorithm are demonstrated by numerical examples. >

Totally automated switching operation in distribution system

Several algorithms and methods that tend to be overlooked but are important for the realization of an automatic and systematic switching operation in a distribution system are proposed. To explain the importance of these algorithms and methods, the concept of an operating state is introduced and the correlation of different purpose switching operations is illustrated. Each proposed algorithm or method is proved to be practical by real scale simulation or a field test. >

On voltage stability from the viewpoint of singular perturbation theory

Abstract This paper investigates voltage stability problems based on singular perturbation theory. The application of singular perturbation theory has made it clear that a power system can be approximated by two simplified systems S and F, which respectively correspond to slow and fast subsystems; four types of voltage instability are defined as follows: • • type I voltage drop, in which the system still has restoring force to its operating point; • • type II voltage collapse, in which the system loses the capability of keeping its operating point. This is divided into the following: 2.1. II-1 instability due to dynamic factor with slow responses such as tap-changing transformers, movement of centre of inertia, load changing patterns; 2.2. II-2 instability due to fast response dynamic factors such as load characteristics, generators, AVR, etc. This kind of instability consists of the following two types: 2.2.1. II-2S static bifurcation, 2.2.2. II-2D dynamic bifurcation. Several features of each type of instability are studied as well as their methods of analysis. Voltage instability tends to begin with type I and then lead to one of the remaining types. The load flow Jacobian can be an effective index to approximately assess types I and II-2S instabilities, while types II-1 and II-2D require direct nonlinear analyses and eigenvalue analyses, respectively. Another point to be noted is concerned with the stability at multiple load flow solutions: it is emphasized that the lower of the multiple load flow solutions can be a stable operating point in some cases, even though most of such operating conditions belong to the type I instability; this situation can occur unless the system encounters the type II instability. The validity of the classification proposed here has been verified through numerical simulations and theoretical analyses which take into account the dynamic characteristics of generating units, loads and tap-changing transformers.

Expert system for designing transmission line protection system

This paper presents a powerful expert system (ES) which makes a basic design of an adequate protective relaying system based on the knowledge of skilled protection engineers. Following the basic design, the ES carries out the relay setting and its validation by means of the integrated power flow and fault calculation programs. Furthermore, the ES has a capability of securing coordination among separately set relays. It is very flexible in that it is able to reset the relays according to power system changes. The effectiveness has been demonstrated by using a part of the Chugoku Electric Power Company System.