Search

In a deregulated power market, customers would have more choices for their power service and the improvement of service quality has become a challenge to power transmission and distribution companies. Distribution system reliability that was traditionally considered within the planning activities is now incorporated in the operational environment. This paper presents study results of a multiobjective feeder operation optimization problem that considers how to balance network efficiency, switching and reliability costs in a distribution network. The proposed method divides annual feeder load curve into multiperiods of load levels and optimizes the feeder configurations for different load levels in annual operation planning. Customer load profiles and seasonal varying data of feeder section failure rates and customer interruption costs are considered. Numerical simulations demonstrate the time-varying effects on the optimal distribution feeder configuration and operation costs. A binary particle swarm optimization (BPSO) search is adopted to determine the feeder switching schedule. Test results indicate that not considering time-varying effects and using only simplified fixed load and reliability parameters could underestimate the total loss to the utility and its customers. Index Terms--Customer interruption cost, distribution feeder reconfiguration, distribution system operation, system loss, system reliability.

This paper presents a method for predicting the number of equipment disruptions due to voltage sags in a unit of time based on a concept described in IEC 61000-3-7. The proposed method uses the probabilistic distributions of system disturbance and equipment immunity indices obtained from a unified fuzzy inference engine to represent the disturbance severity and equipment susceptibility of voltage sags. It takes stochastic behavior of service performance into account in the estimation of equipment disruption. The proposed framework is also applicable if other power-quality indices, such as the voltage sag energy index and voltage sag severity index, are adopted. It can be used as an alternative for performing voltage sag coordination and financial analysis. Index Terms--Disturbance level, equipment disruption, fuzzy index, immunity level, power quality (PQ), voltage sag.

Reliability indices have been used for many years to quantify the effects of sustained interruptions on the electric power system. Criteria for representing and reporting the voltage performance are still under development. A proper voltage sag index would be useful for indicating the system performance experienced at different locations. This paper presents an application of fuzzylogic techniques to quantify voltage sags disturbance levels. Retained voltage magnitude and sag duration are the inputs of the proposed system. The output is an index that indicates the relative severity of a voltage sag event. The proposed framework takes network vulnerability, equipment sensitivity, and uncertainties in measuring voltage sags into account, thereby providing meaningful information for both the utility and customers. Fuzzy sets membership functions and inference rules involved in the inference process are described and field data are used to illustrate the analytical resuits. Using the proposed method, site performance indicators can be obtained from the single event indices of all events recorded. The proposed method brings new analytical insights into the assessment of service performance. Index Terms--Disturbance level, fuzzy set, power quality (PQ), single event index, voltage sag, voltage sag index.

A two-point estimate method is proposed in this paper to assess the power transfer capability uncertainty. This paper assumes that the uncertainty of the line parameters and bus injections involved in transfer capability calculations can be estimated or measured and shows how to estimate the corresponding uncertainty in the transfer capability. Instead of using a large number of simulations as required in the Monte Carlo approach, for a system with n uncertain parameters, the two-point estimate method uses 2n calculations of transfer capability to quantify the uncertainty. The proposed method uses a numerical method to calculate the moments of the transfer capability. The moments are then used in the probability distribution fitting. Using the obtained transfer capability uncertainty information and a desired level of reliability, an adequate transmission reliability margin can be determined for each transmission service. The proposed method can be used directly with a deterministic computer program and it does not require derivatives of the transfer capability. Test results of the proposed method are compared with those obtained from the Monte Carlo simulations and a truncated Taylor series expansion method. Index Terms--Point estimate method, transfer capability, transmission reliability margin, uncertainty.

This paper introduces a new approach to customer interruption cost evaluation that recognizes the dispersed nature of the cost data. The proposed method is designated as the possibility distribution approach and provides a realistic and effective assessment of the losses incurred by high-tech industry electrical users due to power failures. Fuzzy linear regression models are used to describe the distribution and dispersed behaviors of interruption costs. Bootstrap technique is used to generate a sampling distribution of small samples so that confidence intervals of interruption costs of different high-tech sectors can be obtained. Using the obtained cost models, interruption costs and reliability worth of high-tech industries that require higher reliability and premium power service, can be properly assessed. Index Terms--Fuzzy regression, interruption costs, reliability worth.

The model used for real-time network security and transmission capability analyses requires the use of a large area network and has to be brought up to 'real-time' conditions. To build a complete network model, supervisory control and data acquisition (SCADA) data have to be made available to many external bodies. In this paper, an Internet interface to SCADA systems is proposed for inter control center data exchange. A discrete event technique is utilized to simulate the interarea data exchange. The performance modeling of data exchange on the Internet is established, and a quantitative analysis of the data exchange delay is presented. Simulation and experimental results have indicated that the Internet provides a convenient way for intercontrol center data exchange and, by using state estimation (SE) accurate complete network models, can be obtained for practical security and available transfer capability analyses. Index Terms--Communication network simulation, complete network model, intercontrol center data exchange, security analysis.

In a competitive power market, locations of future load growth have to be described with sufficient geographic precision to permit valid marketing strategy and siting of future T&D equipment. Small area load forecast which provides information of future electric demand that includes spatial and temporal characteristics, is useful for T&D and market planning. Domain experts for spatial load forecast require long term practicing and are difficult to find. In order to capture the meaningful associations between spatial data and the load changes, and to provide a useful tool for spatial load forecast, a data mining technique based on a 'Knowledge Discovery in Database (KDD)' procedure is proposed to determine automatically the preferential 'scores' of land use changes. The proposed spatial modeling approach is an exploratory data analysis, trying to discover useful patterns in spatial data that are not obvious to the data user and are useful in the spatial load forecast. Index Terms--Data mining, fuzzy model, knowledge discovery in database, spatial load forecast.

Most electricity service interruptions are due to failures in the distribution network. In a competitive market, service quality and reliability have become an essential part of the business. In order to enhance the reliability in the distribution system, a value-based method is proposed in this paper to take load distribution changes into account and search for new locations of feeder sectionalizers such that the customer interruption costs (CIC) can be reduced. Two stages are involved in the search. Using local information, the first stage determines the search direction and, in the second stage, it decides whether a crossover of the load point is beneficial. To avoid being trapped in a local minimum, a mutation technique is also applied to look for the global optimum. Actual feeders were used in the tests and test results have shown that with a proper adjustment of the feeder sectionalizers, service reliability can be improved and the customer outage costs are reduced. Index Terms--Customer interruption cost, distribution reliability, SAIDI, sectionalizer relocation, value-based planning.

Due to many unforeseen circumstances that could happen in the today's bulk power system, there is a possibility of a system wide outage. In order to provide aids to the power system dispatchers following a complete collapse of the power system, a prototype package has been developed. Through interactive and friendly graphic interface, the package suggests a guideline for the dispatcher to restore the power system. With an aim to increase the ease of maintenance, object-oriented technique was adopted to implement the package. The development of the software involved three stages: 1) Object oriented analysis, 2) Object oriented design, and 3) Integration and testing. In this paper, the structure and the development procedure of the prototype system are presented. Keywords - power system restoration, object-oriented technique

In current power system operations, transmission networks have been operated at their limits much more frequently and for much longer periods of time. Special protection systems (SPS) are attractive for increasing transmission capacity in a competitive market, but the installation costs and system reliability issues are important. In this letter, a risk-based method is proposed to take the uncertainty of contingency occurrence and impacts into account to provide an essential set of contingency cases for SPS implementation. Index Terms--Contingency selection, risk-based security assessment, special protection systems (SPS).

The ability of a regression tree method to properly interpolate among recorded data to give an estimate of the frequency decline following a generator outage is examined in this letter. The proposed method is a nonparametric technique that can select those system characteristics and their interactions that are most important in determining the relation between the generation/load imbalance and the frequency decline. The information obtained from the proposed method can be used online for scheduling fast-acting reserve or load shedding for severe generator outage incidents. Index Terms--Frequency control, generation/load imbalance, load shedding, regression tree, spinning reserve.

In an interconnected power system, the network security and power transfer capability analyzes require a complete network base case solution. With the advent of communications among operations control center computers, real-time telemetered data can be exchanged for complete network modeling. Measurement time skew is a consideration when combining large area data received via a data communication network. In order to accommodate the effects of randomly varying arrival of measurement data, this paper presents an implementation of a stochastic Extended Kalman Filter (EKF) algorithm, which provides optimal estimates of interconnected network states for systems in which some or all measurements are delayed. The method relies on the delay statistics of exchanged data arrival at the control center and the delay is assumed to have a binary statistics, i.e., either the measurements arrive in time or it is delayed by one time sample. Performance of the proposed method is compared with that of the standard Weighted Least Square (WLS) technique. Index Terms--Data exchange, Kalman filter, measurement delay, state estimation.

Adoption of the IEC flicker standard by IEEE would encourage countries currently using \DeltaV10 flicker standard to consider either updating the \DeltaV10 calculation to make it more suitable for modern day applications, or switching to the IEC standard. In the process of revising the flicker standard, the design of flicker planning level is important. For this purpose, this letter presents comparative statistical analyses of flicker measurements based on present Pst and \DeltaV10 standards. Besides the comparison of synchronous flicker severity indices in 10-min intervals, analyses are also conducted using daily flicker statistical reference values measured at the point of common coupling (PCC) of ac and dc electric arc furnace facilities. [ABSTRACT FROM AUTHOR]