The Gas Dispatcher Operating Tool (GDOT) is a computerized dispatching aid for the Gas Dispatcher in San Diego Gas & Electric Company's (SDG&E) Gas Operations Control Center (GOCC). GDOT is an integrated computer hardware and software system which models SDG&E's gas transmission and major distribution systems enabling the Gas Dispatcher to predict whether a given operating strategy will meet anticipated gas demands. GDOT can also be used by the Dispatcher and Engineer to improve the gas system's performance and increase the ability to meet gas demands by comparing various operating strategies in a short time period. GDOT will also be used to train new Gas Dispatchers and to help assess system capacity during systems emergencies. GDOT is not designed as a real-time monitoring system, but rather it is designed to operate in an "on-demand" environment. In 1988, SDG&E first investigated the possibility of developing a GDOT type tool with Stoner/DRF.M. The study focused on estimating the potential benefits gained from GDOT and comparing them to the costs of development to determine if GDOT was feasible and economical. Also, the study was intended to determine whether a steady state or transient analysis would be appropriate for the tool. Results of the feasibility study showed that 25%-30% savings in operating costs (mainly compressor fuel) could be achieved if such a tool were implemented for gas dispatching purposes. In 1989 SDG&E management committed to proceed with developing GDOT. Development was completed by June 1990.

I. Introduction

Each day our dispatchers at SDG&E are faced with a myriad of dispatch decisions that dictate system operations to meet daily gas requirements. SDGGE's transmission system is not really a pure transmission system in the truest sense nor is it a distribution system. It is comprised of compressor stations and large diameter pipelines. Unlike a large interstate transmission system, the SDG&E system must rely upon daily packing and drafting of its transmission pipeline to meet gas loads which vary each day. SDG&E's system is transient by definition. SDG&E dispatch operation demands the attention of a dispatcher. They must continually monitor system pack targets, hourly purchase and sendout; and start and stop compressors to meet daily packing requirements. This effort defines a daily operating strategy. Fortunately, SDG&E is blessed with very experienced gas dispatchers that, for years, have been able to mentally assess system performance with a minimum of manual calculation and arrive at a daily operating strategy to meet daily gas load requirements. These strategies often consist of when to start and stop compressors at SDG&E's primary compressor station located at Moreno, California. In 1986 SDG&E added an additional 6,000 HP (2 Cooper Compressor units) at Moreno and doubled the station's capacity. This presented new operating and system dispatching challenges to our gas dispatchers. These new units had different operating characteristics than the old units and, when running, could pump about twice the flow that one or' the older units could. It had been fourteen years since compressors were added to SDG&E's system.

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