ABSTRACT

Operability and reliability of modern day gas transmission networks could be enhanced by application of various techniques or tools provided by automatic control theory. Some basic tools supporting the dispatcher are well known, for example modelling and simulation of the transient gas flow process. But some gas transmission companies are still less familiar with other power full techniques, like state estimation, state estimation based supervision and failure detection, or predictive optimization. This paper presents a network state observer for solving the state estimation problem, i.e. the task of quasi continuous estimation of the complete instantaneous network state of pressure and flow from a small number of direct measurements. We discuss the design of a network state observer, and its implementation as a general purpose software package. The performance of the observer for state estimation and failure detection purposes is demonstrated by results from field tests and industrial on-line applications.

1. INTRODUCTION

For a long time supervision and control of large gas transmission systems has mainly been based on the dispatcher. Besides more or less up-to-date SCADA-systems only little support has been available. Though dispatchers are highly skilled, today it is necessary t o support them by additional tools. Some reasons for this necessity are the enlargement of transmission systems, the more and more time varying loads due to energy conservation strategies of all customers, higher safety requirements, and, of course, a reduction of cost of network control. At the Chair and Laboratory o f Automatic Control of the Technical University of Munich a research project has been started in 1974 in order to develop and realize advanced tools which can support the dispatcher of a gas transmission system in solving his difficult task. Today, these tools are available, and some thirty European companies are already using them as new standard support equipment. In section 2 of our paper we will start with a summary of some well - known, but essential facts : the general task o f a dispatcher and the drawbacks of conventional, i.e. only SCADA-based, dispatching. Then we will show in short how more sophisticated tools based on transient simulation can improve supervision and control of gas transmission systems. We will see that state estimation is a pre requisite for the application of such tools. State estimation means continuous on-line estimation of the instantaneous state of pressure and flow of the total pipe line network. In section 3 we will discuss some approaches to tackle the state estimation problem, especially by using a so-called network state observer. Section 4 presents in more detail this observer approach. We will discuss its mathematical description, its design and realization as standard tool. In section 5 we will show some results from applications of this network state observer for state estimation and failure detection purposes.

2. ADVANCED VERSUS CONVENTIONAL PROCESS MONITORING AND CONTROL

The operator of any gas transmission system is continually trying to satisfy three main objectives: disaster prevention, fail-safe gas supply, economical dispatching.

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