Safety conditions in manholes in the vicinity of substations

In many cases, the manholes for maintaining various installations including power and telecommunication cables, water-, remote heating-, and gas-pipes are located in a close vicinity of power substations. The paper analyzes the risks of the occurrence of dangerous potential differences within the manhole and on the surrounding ground surface during ground faults in the substation. Possible protective measures are discussed.     

Earthing effects of uncoated underground cables and transferred potentials

Contents A model for the analysis of earthing effects of uncoated metallic sheathed underground cables is suggested. The model includes the proximity effects between the cable sheath and the earth electrodes of the transformer stations at the cable's terminals. Diagrams for assessing apparent sheath impedances to earth as well as transferred potentials and dangerous voltages at terminal stations are constructed appropriate for practical design.

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Wirkung von Erdkabeln mit nichtisolierten Mänteln und die erzeugte Potentialverteilung

Übersicht Ein Modell für die Analyse der Erderwirkung von Kabeln mit nichtisolierten Mänteln wird vorgestellt. Das Modell berücksichtigt die gegenseitigen Beeinflussungen zwischen Kabeln und Erderanlagen an den Kabelenden. Diagramme für die Beurteilung der Erdausbreitungsimpedanzen von Kabeln, der erzeugten Potentialverteilung und Berührungs- und Schrittspannungen entlang der Kabeltrassen werden für die praktische Anwendung angegeben.

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List of symbols J fault current at the HV/MV station flowing into the earth - u _k potential of earthing system elementk - i _k current emanating into the soil from elementk - E _t,E _s touch- and step-voltages - Y longitudinal admittance of a cable sheath segment - Y _n admittance to earth of the earthing structure bonded with the terminal station earth electrode - r _kj mutual earth resistance for elementsk andj - r _kk self resistance to earth of elementk - r _kM mutual earth resistance of elementk and pointM - Z _eq equivalent system impedance to earth as viewed at HV/MV station - Z _a apparent cable's impedance to earth - l(l ₁) cable (characteristic) length - s sheath's segment length - H, d cable's depth of burial and diameter - D diameter of the equivalent plate modeling HV/MV station electrode - l _r,d _r rod length and diameter - earth resistivity     

Iterative Method for Steady State Reliability Analysis of Complex Markov Systems

An iterative procedure for evaluating steady-state probabilities of complex Markov systems is proposed; it is based upon a generalization of Seidel's method for solving systems of linear algebraic equations. The probabilities are evaluated with desired accuracy by sequentially solving equation sets of much lower order than this of the entire system. For the systems with states transmitting only to states of higher and (or) lower probability magnitude orders, simple, easily composable recurrent formulas for state probabilities are obtained. An illustrative example is included.     

Security modeling for power system reliability evaluation

This paper presents conceptual development, computation procedure and simulation results of the methodology for modeling security within reliability evaluation of power systems. The proposed approach takes into account activation of protection and automatic controls, local actions of operators, as well as centralized decisions taken by system operators. Transient stability, frequency variation during governor control, emergency and normal levels of line thermal protection, automatic generation control, overload rotation and economic dispatch are the main points of the developed procedure. It can be directly incorporated into the hybrid model for reliability evaluation of different operating states     

Subacute bacterial endocarditis masquerading as type III essential mixed cryoglobulinemia

An adult man presented severely ill with vasculitis of his lower extremities and with impaired kidney function. After detailed evaluation at a local hospital, a diagnosis of essential type III cryoglobulinemia was made. High-dose steroid and cyclophosphamide therapy was begun. The patient improved dramatically. However, 6 wk later when his steroid dose was reduced to 30 mg daily, vasculitis recurred. Intensifying his immunosuppressive therapy only worsened his condition. He was than transferred to the Ohio State University Medical Center for consideration for plasmapheresis for the presumed essential type III cryoglobulinemia. However, our evaluation showed that he had bacterial endocarditis causing his type III cryoglobulinemia. When immunosuppressive drugs were stopped and antibiotics were begun, his condition resolved completely. This case illustrates the difficulty of identifying infectious causes of cryoglobulinemia and emphasizes that an initial, highly favorable response of vasculitis to immunosuppressive therapy does not exclude an infectious cause for the vasculitis.     

Exact enumeration of minimal paths of partitioned networks

The accuracy of the available approximate approaches for the enumeration of minimal paths of networks decomposed into two sub networks through a cut is discussed and two theorems on the sufficient conditions for a sound application of these approaches are formulated. A method is suggested which extends the applicability of the partition approach for an exact reliability analysis of composite networks with an arbitrary number of sub networks common nodes. Two illustrative examples are also included.     

Digital calculation of earthing systems in nonuniform soil

Contents The mathematical model of earthing systems consisting of straight-line elements in the nonuniform soil is developed. The method presented enables the evaluation of all earthing system characteristics by applying a general algorithm, appropriate for digital computing, based upon elementary data of the earthing system and soil configuration.

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Digitale Berechnung von Erdungsanlagen im inhomogenen Erdreich

Übersicht Es wird ein mathematisches Modell für die aus geradlinigen Elementen zusammengesetzten Erdungsanlagen in geschichtetem Erdreich entwickelt. Die vorgeschlagene Methode ermöglicht die Berechnung aller Kennlinien der Erdungsanlage bei Anwendung eines allgemeinen Verfahrens, das auf der elementaren Daten über die Konfiguration der Erdungsanlage und des Erdreiches beruht.

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List of Symbols u electric potential (voltage) - e _c contact voltage - e _p pace voltage - i,i _g current - R resistance to earth - r self or mutual resistance - ₁ earth resistivity of the upper soil layer - ₂ earth resistivity of the bottom soil layer - n depth of the upper soil layer - l length of the earthing system element - d diameter of the earthing system element - V general symbol for the rectangular space coordinatesX, Y, Z of a point - R(M, K) distance between pointsM andK Other symbols are defined in the text.     

Optimal planning of rural medium voltage distribution networks

A model is suggested for selection of main initial parameters and timing of the reconstructions of rural distribution networks in long-term planning to meet the increasing load demands with minimum total present worth cost. The model incorporates capital and exploitation costs as well as the costs due to undelivered energy and load curtailments. The optimal investment policy is determined using a constrained dynamic programming technique which indicates the best choice among possible options while taking into account all relevant technical criteria and common-sense rules.     

Rationalization of operation of an industrial network

The paper deals with the rationalization of the electric power supply of an industrial network. The relevant indices characterizing daily load diagrams are defined, and measurement data are statistically processed to select the representative days for the optimization of reactive power compensation. Mathematical models for the optimization of compensation and load shifting are provided and efficiently processed by applying the Hooke and Jeeves’ discrete search approach. Optimal allocation of capacitor banks at available network load points and their sizes have been determined to maximize the annual cost saving related to real and reactive energy consumption charges. The optimal solution recommended is analyzed for harmonics resonance conditions. The optimal phase shifts of daily load diagrams of feeders supplying various groups of loads are determined potentially minimizing the peak of the aggregated load and associated charges.