A.S. Farag

Economic load dispatch multiobjective optimization procedures using linear programming techniques

This paper outlines the optimization problem of real and reactive power, and presents the new algorithm for studying the load shedding and generation reallocation problem in emergencies where a portion of the transmission system is disabled and an AC power solution cannot be found for the overloaded system. The paper describes a novel and efficient method and algorithm to obtain the optimal shift in power dispatch related to contingency states or overload situations in power system operation and planning phases under various objectives such as economy, reliability and environmental conditions. The optimization procedures basically utilize linear programming with bounded variables and it incorporates the techniques of the Section Reduction Method and the Third Simplex Method. The validity and effectiveness of the algorithm is verified by means of two examples: a 10-bus system and the IEEE 30-Bus, six generators system. >

On-line partial discharge calibration and monitoring for power transformers

Partial discharge (PD) is one of the major factors causing insulation damage of power transformers. This paper describes the development of on-line partial discharge monitoring system for transformers. The developed set can monitor up to four power transformers continuously. It uses various methods to reject interference and enhances monitoring sensitivity of PD effectively. The optical cable is applied to communicate between measurement system near transformers and the upper computer in the main control building. On-line calibration of partial discharge quantity is requisite for on-line detection or monitoring. This paper describes an on-line calibration method using pulse injection through tap of high voltage transformer bushings. It also discusses the influence of limit inductance and bushing capacitance, from tap of bushing to ground, in on-line calibration circuits. Influences of multi-grounding of the transformer tank for monitoring and calibration are also discussed. Simulation in laboratory and site test shows that the method is practically valid for on-line PD calibration of power transformers within permissible engineering error range under certain defined conditions. This system has been in operation steadily in 500 kV substations for more than 2 years.

Occupational exposure assessment for power frequency electromagnetic fields

Exposure assessment is the determination or estimate of the magnitude, frequency of occurrence, and rate of exposure of an individual or a group to an environmental agent. The agents of interest in this case are the electric and magnetic fields (EMF) in the extreme low-frequency range that includes the power frequency of 50/60 Hz. There are an increasing concern that exposure to EMF may be associated with biological and health effects. This concern has prompted numerous measurement projects and the development of instrumentation, methodologies, and exposure models and simulations. This paper identifies the status of EMF exposure assessment research related to occupational exposures. It draws the recent results to emphasize the unique aspects of EMF exposures in the home and utilities environments, and highlights the research needs. The intensities of electromagnetic fields have been measured under power transmission and distribution lines, at substations and industrial plants and near various electric devices including domestic electrical equipment. The field intensities have been related to the exposure time (duration of staying) in the different areas and have been compared with the internationally established standards. The data presented are useful for understanding the levels of electromagnetic fields that can be encountered in various places and also for estimating possible occupational and residential exposure levels.

Underground cable magnetic field simulation and management using new design configurations

This paper addresses one of the most important sources of magnetic fields: underground power cables. New design configurations for one, two, three and four cables per phase are presented from a magnetic field perspective. Different management techniques are studied in detail. Judicious placement of cable phases in multiconductor lines to reduce the field effect is implemented by computer modeling and simulations. The state-of-the-art magnetic field simulation package PCFIELD developed by EPRI is used to quantify and present the tool used to manage the field values. The new design configuration cases are very useful from a magnetic field point of view and have low cost schemes that can be easily implemented.

Implementation of shielding principles for magnetic field management of power cables

Adverse health effects due to magnetic fields is a matter of great concern and has been widely debated in recent years. Managing these fields is a challenge to researchers. One of the important sources of magnetic fields is power cables. Different management techniques have been studied. In this paper, passive shielding schemes are implemented to manage the magnetic fields of power cables. The various shielding schemes can be separated into two broad categories: shielding subject and shielding source. Both schemes are implemented in this paper. Passive shielding schemes are found to be the most powerful technique as the reductions obtained are sometimes as high as 97-98%. This scheme is a costly one, should be used only in assigned locations, and as such, there has to be a trade-off between the cost and the level for reduction desired and the health desired and the health hazards.

Magnetic field management techniques in transmission underground cables

Magnetic field management is concerned with the minimization of the effects of such fields on the public health, without sacrificing the effectiveness or reliability of the power system. The essential management techniques used for the underground transmission cables comprise geometry manipulation phase placement, and source shielding. In this paper, the simulation results of the standard recommended stack, triangular and flat configurations are presented. The simulations have been carried out for single and three phase cables. The resulting fields for different depths have been evaluated and compared. The results led to the conclusion that judicious placement of phases is a very powerful management technique to reduce the magnetic field as cost has not been changed. The appropriate phase placements corresponding to minimal field values are obtained.

Transient approximation of a bilinear two-area interconnected power system

Abstract A balancing model reduction scheme for high order bilinear systems, similar to the linear balanced reduction algorithm, is applied to power system modelling. An original 17th-order two-area interconnected bilinear power system is reduced, using both linear and bilinear balancing algorithms, to a 10th-order reduced model. Overall superiority of the bilinear reduction scheme over linear balancing is observed in the performed simulation study. The reduction scheme also leads to a very acceptable approximate response compared with that of the original system.

Failure Analysis of Composite Dielectric of Power Capacitors Used in Distribution Systems

This paper describes the study of the reliability of capacitor units installed and operated in distribution system during the period 1980 through 1990. Failures of capacitor units in distribution substations can be very costly to the supply of reliable power to consumers. To enhance utility reliability, failure analysis, and rates, failure origin and physical damage causes were performed for these capacitor units. Two approaches, statistical and physical, were utilized in this study. In the statistical area, failure modes, reliability levels and failure causes are analyzed. The physical study mainly deals with the mechanism of deterioration of the composite dielectric. This paper models capacitors failure mathematical mode and calculates their failure rate. The results of the study of 2912 capacitor banks including 8736 capacitors installed at 153 distribution substations showed that the failure mode of capacitor units may be represented by Weibull distribution and each capacitor manufacturer has a diffe...

New comprehensive reliability assessment framework for power systems

Existing reliability assessment methods are not consistent, and the approaches used produce inefficiencies in resource allocation. In this paper, a comprehensive new probabilistic reliability assessment framework is proposed and new reliability assessment methods and approaches are developed. Novel approaches dealing with probabilistic voltage stability analysis, angle stability, power balance and integrated reliability planning for bulk power systems are also developed in this work. Seven performance states have been proposed to define the power system conditions. System issues and a Markov model defining these states are also presented. New probabilistic voltage and angle stability assessment approaches are developed, including new voltage stability measures (Q-indices) based on machine and system reactive margins. Application consideration of the new reliability framework is also presented. All model developments were tested with a real electric power system of the western U.S.A.

Voltage stability estimation and prediction using neural network

This paper proposes a neural network-based method for on-line voltage stability estimation, prediction and monitoring at each power system load bus. The training of the radial basis function neural network (RBFNN) was accomplished by using load flow voltage magnitude and phase as input information, and fast indicators of voltage stability information covering the whole power system and evaluated at each individual bus as output layer information. The generalization capability of the designed networks under a large number of random operation conditions and for several power systems has been tested. Fast performance, accurate evaluation and good prediction for the voltage stability margin have been obtained. Results of tests conducted on standard IEEE 14-bus test system are presented and discussed.