Approximate steady-state solutions for Markov systems based upon the transition-rate matrix deviation concept

This paper derives an approximate method for solving the steady-state Markov equations. The approximate solutions are determined using the known or easily obtainable solutions of a Markov system whose transition-rate matrix slightly differs from that of the original system. The method suggested makes it possible to derive approximate analytic expressions for the steady-state probabilities of system states and associated reliability indices and/or to calculate their numerical values. The expressions for the error bounds for the method are provided. The method is applied to derive expressions for the state probabilities of two transmission lines sharing the same right of way and exposed to common cause failures, as a demonstration.     

Power system operating cost and committed generation capacityplanning

A realistic simulation model is presented for the evaluation of generating units variable cost and the cost of undelivered energy, taking into account existing limitations and uncertainties. A criterion for committed capacity reserve planning is also suggested, aimed at minimizing the total power system operating cost. The model and the committed capacity reserve planning criterion are applied to the IEEE RTS, for demonstration purposes     

Grounding effects of HV and MV underground cables associated withurban distribution substations

This paper derives a model for the evaluation of the performances of composite grounding systems of urban main distribution substations and associated power cable networks. The effects of the cables upon the dangerous voltages, transferred potentials and ground fault current distribution are encompassed including the conductive and magnetic coupling among grounding system elements, as well as the nonlinearity of cables sheaths impedances. An application example is presented, as are some experimental data     

Maximum step voltages of combined grid-multiple rods groundelectrodes

Expressions are suggested for assessing the maximum step-voltages and associated parameters of combined grid-multiple rods ground electrodes buried in uniform soil. The expressions proposed are successfully verified by comparison to exact computer calculations performed for a wide set of square and rectangular ground grids reinforced by ground rods distributed around the grid perimeter and within the grid     

Sensitivity analysis of experimentally determined grounding gridimpulse characteristics

The paper presents an experimental determination of the grounding grid impulse characteristics procedure. The measuring circuit configuration and characteristics of the applied equipment are given. Some of the numerous experimental results for three grounding grid configurations are presented. The paper provides the analysis of the results obtained for various impulse current shapes, magnitudes and discharge points. The results shown are related to the cases without soil ionization around the grid elements     

Optimal sparing strategy for a group of substations

The authors derive a method to optimize the sparing of the equipment for a group of substations during a planning period. The amount of spares which have to be stored at the beginning of each year is optimized to achieve the minimum total cost associated with sparing, which includes the investment cost for spares and the load curtailment and loss of revenue costs. Various sparing strategies are evaluated, including common and individual-inventory concepts. The application of the method and the benefits it provides when compared to other sparing concepts are demonstrated for several typical examples     

Enumeration of minimal paths of modified networks

A method is presented for enumeration of minimal paths of networks generated by sequential modifications of an initial network, based upon step wise reformation of minimal paths sets associated with network modifications. The method can be applied for an effective enumeration of minimal paths of various extensions and reinforcements of an existing network in the network reliability analysis for the expansion planning. An illustrative example is included.     

Nonuniformity correction factors for maximum mesh-voltages ofcombined grid-multiple rods electrodes

Correction factors for evaluating maximum mesh-voltages associated with combined grid-multiple rods ground electrodes in two-layer soils are calculated for a wide set of ground electrodes to expand the application of available uniform soil expressions to nonuniform soil cases. Square and rectangular grids are examined reinforced by rods of fixed length distributed along the grid perimeter only and along the grid perimeter and grid diagonals. Results of the calculations of 2200 cases generated by varying electrodes and soil parameters are displayed as graphs appropriate for practical application. Approximate analytical expressions for correction factors are also derived matching reasonably well with the calculated data. These expressions offer an insight in the most effective ground electrodes parameters which might serve in the design process     

Failure-Frequency Evaluation of Complex Systems Using Cut-Set Approach

The paper develops a new method for evaluating failure frequency of complex systems with 2-state components, from corresponding cut sets. The method is derived by direct application of cut-set techniques to the failure frequency formula obtained by Buzacott and Singh. The method is suitable for computer implementation and can be used for cut-set diagrams with overlapping and non minimal cut-sets. Two examples are presented and the results are compared with those obtained by a common approximate approach.     

Modeling the base load generating units with derated states in composite power system reliability evaluation

Contents A novel approach for the construction of the equivalent two-state models for base load generating units with derated states is suggested in order to reduce the computational burden in composite power system reliability (adequacy) evaluation. The proposed equivalent is conceived in such a way to preserve the invariance of the failure probability of the generation system taken alone, under assumption that the network effects upon the generating units models are slight and can be ignored. The equivalent model suggested has been successfully tested and compared with the EFOR based model for the IEEE RT System.

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Modellierung von Grundlast Generator-Einheiten mit geschwächten Zuständen in der Berechnung der Zuverlässigkeit von elektrischen Verbundsystemen

Übersicht Ein neues Verfahren für die Zusamenfassung von den Zwei-Zustand Ersatzmodellen für die Grundlast Generator-Einheiten mit geschwächten Zustäden wird vorgeschlagen, um die Rechneranlagen-Anforderungen zu vermindern. Das entwickelte Ersatzmodell bewahrt die Invarianz der Ausfall-Wahrscheinlichkeiten des allein betrachteten Generatorsystems unter der Voraussetzung, daß der Einfluß von Übertragungs-Netzkomponenten bei Generatormodellen vernachlässigbar ist. Das vorgeschlagene Ersatmodell wird erfolgreich für das IEEE RT-System überprüft und mit dem bekannte EFOR-Modell verglichen.