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Microelectron. Reliab., Vol. 35, Nos 9-10, pp. 1333-1345, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0026-2714/95 $9.50+.00

RELIABILITY ANALYSIS OF INDUSTRIAL POWER SYSTEMS WITH SENSITIVE LOADS

M.H.J. Bollen 1
Abstract A method for the reliability analysis of power system has been developed that includes the behaviour of the systemduring a disturbance. The power system is modelled as an electrical network in which branches are removed and inserted by stochastic events, generated by a Monte Carlo simulation. This method considers short circuits followed by an interruption of the protection, in stead of just the removal of a component. By using a maximum-permissable voltage sag as an interruption criterion the method can beused for industrial power systems with sensitive loads. The (correct and incorrect) behaviour of the protection, ageing of components, and the influence of preventive maintenance are also included in the method. An example of the use of the method is given: a power system feeding four industrial plants. The influence of plant voltage solidity and of preventive maintenance in the feeding network areinvestigated. Both turn out to have considerable influence.

1. Introduction Industrial power systems are often characterized by high costs of

interruption. This makes it necessary to include reliability considerations in the design of industrial power systems. Many industrial power systems use single (or even double) redundancy, automatic transfer systems or emergency generators to obtain ahigh reliability. The reliability

considerations become complicated as industrial plants are often very sensitive to voltage sags (Diliberti et al., 1990; IEEE, 1991; Koval et al., 1992; McGranaghan et al., 1991; Morgan, Ihara, 1991; Mulukutla,

Gulachenski, 1991 ; Spijkers, 1989; Warren, 1991 ;). In 1989 the Group of Electrical Energy Systems of Eindhoven University Eindhoven University ofTechnology, Group of Electrical Energy Systems, Eindhoven, The Netherlands. Currently at UMIST, Dept. of Electrical and Electronic Engineering. Manchester, UK.
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M.H.J. Bollen

of Technology started a research project after reliability and design of industrial power systems. The research was performed in cooperation with Tilburg University and some large compagnies (Bollen eta1.,1990). One of the results of this cooperation is a computer program for reliability analysis of industrial power systems with sensitive loads (Bollen, Massee, 1992). The method on which the program is based includes the influence of voltage sags on those sensitive loads. This method considers short circuits followed by an intervention of the protection in stead of just the removal of a component.The power system is modelled as an electrical network in which branches and nodes are removed and inserted by stochastic events. After each event the voltage at the plant busses is calculated by using the electrical network. A maximum permissable voltage sag is used, for each plant different, as an interruption criterion. If the voltage shape during a disturbance comes below the maximumpermissable sag of a load, that load experiences an interruption. The (correct and incorrect) behaviour of the protection, ageing of

components,

and the influence of preventive

maintenance are also

included in the method.

This paper will first give an overview of the power system model used. The paper will go into some details of the interruption criterion and the protection model. To showsome of the possible applications of the method, an example of its use is given.

2. Basic parts of the method

2.1. Overall structure

In this method a Monte Carlo simulation is combined with an electrical network model; the overall structure is shown in Figure 1. The Monte Carlo simulation method generates events in "stochastic components" (e.g. the occurrence of a short circuit in a...