Jae-Haeng Heo

A Reliability-Centered Approach to an Optimal Maintenance Strategy in Transmission Systems Using a Genetic Algorithm

Electric power transmission utilities try to maximize profit by reducing electricity supply costs and operation costs while maintaining their reliability. Developing maintenance strategies is one of the effective ways to achieve these profitable goals. The reliability-centered maintenance approach is a key method in providing optimal maintenance strategies. It considers the tradeoffs between the upfront maintenance costs and the potential costs of reliability losses. Since a transmission system is a group of different kinds of equipment and the reliability of the electric facilities varies with time, an equipment state model using a modified semi-Markov chain is proposed. In addition, a genetic algorithm is used to find the optimal maintenance strategies from a large class of possible maintenance scenarios. These optimal maintenance strategies have been tested on an IEEE 9-bus system and an IEEE 118-bus system; the results show that the proposed method minimizes the total expected costs.

Impacts of Wind Power Integration on Generation Dispatch in Power Systems

The probabilistic nature of renewable energy, especially wind energy, increases the needs for new forms of planning and operating with electrical power. This paper presents a novel approach for determining the short-term generation schedule for optimal operations of wind energy-integrated power systems. The proposed probabilistic security-constrained optimal power flow (P-SCOPF) considers dispatch, network, and security constraints in pre- and post-contingency states. The method considers two sources of uncertainty: power demand and wind speed. The power demand is assumed to follow a normal distribution, while the correlated wind speed is modeled by the Weibull distribution. A Monte Carlo simulation is used to choose input variables of power demand and wind speed from their probability distribution functions. Then, P-SCOPF can be applied to the input variables. This approach was tested on a modified IEEE 30-bus system with two wind farms. The results show that the proposed approach provides information on power system economics, security, and environmental parameters to enable better decision-making by system operators.

Generalized Reliability Centered Maintenance Modeling Through Modified Semi-Markov Chain in Power System

The purpose of power system maintenance is to prevent equipment failure. The maintenance strategy should be designed to balance costs and benefits because frequent maintenance increases cost while infrequent maintenance can also be costly due to electricity outages. This paper proposes maintenance modeling of a power distribution system using reliability centered maintenance (RCM). The proposed method includes comprehensive equipment modeling and impact analysis to evaluate the effect of equipment faults. The problem of finding the optimum maintenance strategy is formulated in terms of dynamic programming. The applied power system is based on the RBTS Bus 2 model, and the results demonstrate the potential for designing a maintenance strategy using the proposed model.

Application of Particle Swarm Optimization to the Reliability Centered Maintenance Method for Transmission Systems

Electric power transmission utilities make an effort to maximize profit by reducing their electricity supply and operation costs while maintaining their reliability. The development of maintenance strategies for aged components is one of the more effective ways to achieve this goal. The reliability centered approach is a key method in providing optimal maintenance strategies. It considers the tradeoffs between the upfront maintenance costs and the potential costs incurred by reliability losses. This paper discusses the application of the Particle Swarm Optimization (PSO) technique used to find the optimal maintenance strategy for a transmission component in order to achieve the minimum total expected cost composed of Generation Cost (GC), Maintenance Cost (MC), Repair Cost (RC) and Outage Cost (OC). Three components of a transmission system are considered: overhead lines, underground cables and insulators are considered. In regards to aged and aging component, a component state model that uses a modified Markov chain is proposed. A simulation has been performed on an IEEE 9-bus system. The results from this simulation are quite encouraging, and then the proposed approach will be useful in practical maintenance scheduling.

Optimal maintenance strategies for transmission systems using the Genetic Algorithm

Electric power transmission utilities not only decrease their operation costs, but also take opportunities to maximize their profit. While they should operate to meet customer needs for reliability which is one of major concerns of power delivery. Therefore they need to make the maintenance strategies considering the tradeoff between cost and reliability. In this paper, Genetic Algorithm (GA) is used to find optimal maintenance strategies for transmission systems. To consider aged and much different equipment, the equipment state model through modified semi-Markov chain is proposed. Also, the effects of equipment failure on the system are presented in terms of a cost using the DC-Optimal Power Flow (OPF). The results on the IEEE 9-bus system show the optimal maintenance strategy which minimizes operation costs.

Study on the Optimal Operation of ESS Considering Urban Railway Load Characteristic

This paper proposes the optimal operation of ESS (Energy Storage System) in the substation of urban railway in an economical point of view. Since the load patterns of urban railway have different characteristics with the general power demand pattern, the characteristics motivate us to develop the optimal operation algorithm for ESS under Korean electricity billing system. We also introduce two different ESS operation strategies for peak load shaving and electricity consumption charge minimization respectively, and formulate each scheme. Historical data from Namgwangju substation are used for economical comparison of the strategies. The results show that the proposed algorithm is the most cost-effective ESS operation scheme among the strategies and reduces around 5 percent of electric charges compared to the charge without ESS operation.

South Korean power distribution system-based operation, market structure and regulation strategies under distributed generation and smart grid

In this paper, we suggest the operation, market structure, and regulation strategies with distributed generation (DG), demand response (DR), smart grid (SM) in the Korean power distribution system. The strategic business unit (SBU) in the Korea Electric Power Corporation (KEPCO) was introduced as an alternative strategy because of the interruptions in the steps of distribution separation in the power generation sector. The SBU is a system which retains responsibility for its own costs through self-regulation by each unit, thus providing incentives for competition, innovation and learning. In the regulatory perspective data envelopment analysis (DEA), the retail price index (RPI-X) regulation algorithm can be used to evaluate the relative efficiency of each unit in incentive based regulation. A distributed distribution power flow analysis can be performed for the calculation of the boundary values of each SBUs information. In this paper, we will consider diverse strategies involving DG, SM, DR, and market regulation strategies in the South Korean power system.

Application of particle swarm optimization for an optimal maintenance strategy in transmission systems

This paper presents the application of particle swarm optimization (PSO) technique to find the optimal maintenance strategy of transmission equipment with minimum total expected cost of generation cost, maintenance cost, repair cost and outage cost. Three types of transmission equipment, the overhead line, the underground cable and the insulator are considered. To consider aging, the equipment state model through modified Markov chain is proposed. Simulation is performed on IEEE 9-bus systems. The results obtained are quite encouraging and will be useful in maintenance scheduling.

Optimal Allocation of Shunt Capacitor-Reactor Bank in Distribution System with Dispersed Generators Considering Installation and Maintenance Cost

This paper proposes the allocation method for capacitor-reactor banks in a distribution system with dispersed generators to reduce the installation costs, the maintenance costs and minimize the loss of electrical energy. The expected lifetime and maintenance period of devices with moving parts depends on the total number of operations, which affects the replacement and maintenance period for aging equipment under a limited budget. In this paper, the expected device lifetimes and the maintenance period are included in the formulation, and the optimal operation status of the devices is determined using a genetic algorithm. The optimal numbers and locations for capacitor-reactor banks are determined based on the optimal operation status. Simulation results in a 69-bus distribution system with the dispersed generator show that the proposed technique performs better than conventional methods.

Economic Evaluation of ESS in Urban Railway Substation for Peak Load Shaving Based on Net Present Value

In this paper, we estimate the economic benefits of Energy Storage Systems (ESSs) for peak load shaving in an urban railway substation using the annual cost. The annual investment cost of ESSs is estimated using Net Present Value (NPV) and compared with the cost reduction of electricity by the ESS. The optimal capacities of the battery and Power Converting System (PCS) are determined for peak load shaving. The optimal capacity of the ESS and the peak load shaving is determined to maximize the profit by the ESS. The proposed method was applied to real load data in an urban railway substation, and the results show that electric power costs can be reduced. Other aspects of the ESS, such as the lifetime and unit price of the battery, are also investigated economically.