Planning engineers are challenged by high residential and industrial growth that place demands on local transmission pipeline systems. Pacific Gas & Electric Company (PG&E) engineers have found that capital investments can be optimized by applying load growth to smaller geographic zones rather than using global growth rates across a large area. Capital investments can be further optimized utilizing a methodology involving future projected growth trends rather than relying on historical growth patterns. PG&E obtained detailed GIS based growth information from cities and counties and incorporated this data into the gas system models. This process made it practical to use the large amounts of detailed growth information. PG&E engineers developed a systematic method to gather and apply growth to local transmission models. This paper will:

  • Provide an overview of how growth was formerly applied to local transmission system models and the issues involved

  • Describe the project goals and solutions that were developed to improve the process

  • Summarize the results and benefits obtained

  • Provide a description of the applications developed The paper will discuss significant efforts by PG&E to streamline the application of growth and develop optimum long range capital investment plans.


One of the most challenging aspects of modeling gas transmission systems is determining demands for residential, commercial and industrial customers. Once a method is developed to accurately determine current customer loads and profiles (see 2004 PSIG Paper 0411, Avella, Jones, Korta, Phelan), the next significant challenge is to project future load growth. The quality of growth information impacts the quality of the analyses performed to support operation and capacity investment decisions. Accurate loading can save millions of investment dollars. Various techniques are used to project growth, with varying degrees of difficulty to apply. An engineer's time to develop growth projections is proportional to the level of model accuracy. Sustained rapid growth continues in the PG&E territory requiring large investments to meet the demand. The objective for developing a growth forecasting technique is to (1) locate growth areas using GIS based information, (2) project the time frame for needed investments, and (3) improve efficiency in projecting growth.

PG&E Gas Transmission and Distribution Systems

PG&E operates one of the largest gas systems in the United States. The service territory covers about two-thirds of the state of California. PG&E delivers about 875 billion cubic feet annually to 4.1 million customers in northern and central California. The gas transmission system consists of approximately 2,000 miles of ‘backbone’ transmission pipeline and 4,300 miles of ‘local’ transmission pipeline operating above 60 psig. Backbone transmission pipeline consists of 3 major pipelines which import gas into California. Local transmission pipelines transport gas from the backbone pipelines to the 40,000 miles of gas distribution pipelines, which operate at or below 60 psig. PG&E employs 9 engineers responsible for long-term capacity planning of 29 backbone and local transmission systems, and 19 engineers responsible for the capacity planning of 237

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