Bundhit Eua-arporn

Defining the must-run and must-take units in a deregulated market

Reliability must-run (RMR) units are generation facilities that are necessary during certain operating conditions in order to maintain the security of power systems in a competitive environment. Absence of RMR units may result in insecure operation of a system. From a financial point of view, RMR units may become a safety net for independent power producers (IPPs) who enjoy steady incomes or a place for those who prefer not to participate in the competitive market. This paper presents a practical method to determine RMR units and their must-run output in the Thailand power market, according to the proposed structure of the Thailand deregulated market to be implemented in 2003 (forecasted opening date of the operation based on information of August 1999). The study determines the amount of must-run output in RMR units by finding the necessary amount of generation to avoid the violation of voltage magnitude, thermal limit, and voltage stability limit. The proposed procedure to determine RMR units defines the amount of generation capacity to be assigned as RMR and allows must-run units to sell surplus generation capacity to the system.

Fuzzy interrupted energy assessment rate based on actual system performance

In competitive environment, customer outage cost may be taken into account for the delivery of energy services. Based on a probabilistic approach the outage cost can be evaluated from the Interrupted Energy Assessment Rate (IEAR) which normally requires customer perception on the damages occurred from an electricity interruption. In general the IEAR is only calculated based on mean values, even though the obtained customer damage information usually contains fairly large deviation. To cope with the large deviation of the data, this paper employs fuzzy arithmetic to model the customer damage function which is consequently used in association with power interruption statistics, rather than conventional probabilistic reliability calculation, to calculate the Fuzzy Interrupted Energy Assessment Rate (FIEAR). The proposed method has been tested with a distribution system of which more than 40,000 actual interruptions were recorded. The results show that the FIEAR normally covers the IEAR and provides flexibility to allow the customer outage cost to be implemented in real competitive environment.

Economic Load Dispatch for Piecewise Quadratic Cost Function using Hybrid Self-adaptive Differential Evolution with Augmented Lagrange Multiplier Method

This paper presents an efficient method for solving economic load dispatch (ELD) problems using a hybrid self- adaptive differential evolution with augmented Lagrange multiplier method (SADE_ALM). Treated as additional control variables, two strategic parameters called the mutation factor (F) and the crossover constant (CR) are dynamically self-adaptive throughout the evolutionary process. Since tuning of the parameters is a tedious task due to complex relationship among parameters, the optimal parameter settings may never be found, and possibly leads to a local optimal solution. An augmented lagrange multiplier method (ALM) is applied to handle equality/inequality constraints. To demonstrate the effectiveness of the proposed algorithm, two ELD problems considering: (1) multiple fuels, and (2) multiple fuels with valve-point effects, are tested and compared with other methods e.g. differential evolution (DE) based methods, modified particle swarm optimization (MPSO), improved genetic algorithm with multiplier updating (IGA_MU) etc. The results show that the proposed SADE_ALM is very effective and provides promising capability for solving the economic load dispatch problem with piecewise quadratic cost function.

AC power flow sensitivities for transmission cost allocation

Under competitive environment of electric supply industry, customers will have options to purchase energy and services from different sources. For this implementation, transmission cost allocation is an important issue to be considered. This paper proposes a method for allocating transmission costs to all participants based on the ratio of incremental power flow caused by each participant and the transmission line capacity. The proposed method employs full AC power flow sensitivity analysis, which provides more accurate results than the ones derived from DC or decoupled power flow. In addition, it can also manage the reactive power transaction. The proposed method has been applied with the case studies of IEEE 30-bus test system. Encouraging results have been obtained.

Evaluating the impact of distributed generation on protection system coordination using protection miscoordination index

Distributed generation (DG) has been considerably increased for several years. However, it may provide negative impacts to the connected distribution system. One important problem is the protection system miscoordination which decreases system reliability. This paper proposes a method to quantify the impact of a DG on protection coordination by using Protection Miscoordination Index (PMI), the value of which shows the probability that the protection miscoordination will occur in the system. The constraints used to indicate the coordination problems are presented and tested. The obtained PMI results from various cases are analyzed. In addition, the maximum allowable capacity of a DG that can be installed to maintain the protection coordination is obtained using PMI.

Real Power Loss Allocation for Transactions in Bilateral Markets

The context of transmission loss allocation raised and debated under restructuring of electric supply industry. It is normally defined as a procedure of allocating or charging all participants for their transmission real power loss. In a traditional theory of electricity spot pricing contribution of transmission loss to inject/withdrawal power at each bus is aggregated in a nodal price as an incremental transmission loss. This term is definitely depended on choice of a slack bus thereby charging based on nodal price is a discrimination even a slack bus is specified beforehand with agreement of all participants. The impact of a slack bus, however, has less affect for allocating loss based on transactions with a specified source and sink under bilateral/multilateral markets. In this paper, the authors proposed methodology for allocating transmission loss to bilateral/multilateral contracts in advance for dispatching in real-time. It is formulated based on a slack bus independent concept associated with a fine tuned algorithm to increase calculation speed. Network topology and system condition are taken into account. The proposed method is tested with a 6-bus an IEEE 30-bus systems, from which the results obtained from the IEEE 30-bus system are compared with the one obtained from a pro-rata method. Promising results are obtained and shown that, for transaction of bilateral/multilateral contracts, the proposed method is more sensible than the pro-rata method.

Transmission system expansion planning with consideration of N-1 security constraints

This paper presents a heuristic method for solving transmission system expansion problems (TSEP) with consideration of N-1 security constraints. The method is divided into two phases. An initial plan is established in the first phase by a search process which is based on a modified simplex method and sensitivity indices. The second phase starts from the initial plan and performs the local search in the defined neighborhood. Additionally, reconstruction of the new lines on the existing right of ways, which is one of the interesting issues of TSEP in the urban area, is taken into account. The proposed method provides very satisfactory results compared with others.

Design of compensators for power systems operating under load voltage fluctuation satisfying bounding conditions

In power systems generation and control, the load variation has a great influence directly on the systems stability and dynamic performances. This paper describes the design of a compensator for a power system subject to random load voltage fluctuation, where the voltage fluctuations are treated as persistent functions satisfying bounding conditions. For stable operation and good performances of power systems, the rotor angle, the terminal voltage and the speed deviation of the generator are required to remain within their prescribed bounds, despite any change in the load voltage. Any violation of the bounds may lead to the systems instability and hence unacceptable consequences. The numerical results illustrate that the proposed design method provides a realistic formulation and therefore is effective for designing power system compensators.

Loss assessment in a low-voltage distribution system

Accurate assessment of power loss in a low-voltage distribution system is still an important issue under present competitive environment. Even though, power flow analysis is still efficient to calculate technical power loss, it requires numerous data which may not be available for some utilities. For this reason, the loss assessment for a low-voltage distribution system is not easy when the demand of any customer load points is still unclear. Therefore, distribution utilities obviously require a more suitable algorithm with their available information to calculate their system power loss. This paper proposes an alternative algorithm to crop with this problem. The proposed approach has been tested with an actual system, a low-voltage distribution system with 16 customer load points. It is found that the proposed method can provide satisfactory results.

Generation system planning with consideration of load forecast uncertainty and energy limited units

This paper presents a method for generation system expansion planning with consideration of load forecast uncertainty and energy limited units. The applied method is based on predefined risk criteria, which is evaluated by a probabilistic methodology to ensure adequate and appropriate power supply for long-term demand. Monte Carlo simulation technique is applied to obtain the results which can be used to assist the decision maker in developing a power expansion plan. The proposed method has been tested with a modified Thailand power system including pumped storage units. The results illustrate the impact of demand uncertainty on the number of new generators needed in each studied year.