1996

Seppälä, Anssi

The topics introduced in this thesis are: the Finnish load research project, a simple form customer class load model, analysis of the origins of customers load distribution, a method for the estimation of the confidence interval of customer loads and Distribution Load Estimation (DLE) which utilises both the load models and measurements from distribution networks. These developments bring new knowledge and understanding of electricity customer loads, their statistical behaviour and new simple methods of how the loads should be estimated in electric utility applications. The economic benefit is to decrease investment costs by reducing the planning margin when the loads are more reliably estimated in electrc utilities. As the Finnish electricity production, transmission and distribution is moving towards the de-regulated electricity markets, this study also contributes to the development for this new situation. The Finnish load research project started in 1983. The project was initially coordinated by the Association of Finnish Electric Utilities and 40 utilities joined the project. Now there are over 1000 customer hourly load recordings in a database. A simple form customer class load model is introduced. The model is designed to be practical for most utility applications and has been used by the Finnish utilities for several years. There is now available models for 46 different customer classes. The only variable of the model is the customers annual energy consumption. The model gives the customers average hourly load and standard deviation for a selected month, day and hour. The statistical distribution of customer loads is studied and a model for customer electric load variation is developed. The model results in a lognormal distribution as an extreme case. The model is easy to simulate and produces distributions similar to those observed in load research data. Analysis of the load variation model is an introduction to the further analysis of methods for confidence interval estimation. Using the `simple form load model, a method for estimating confidence intervals (confidence limits) of customer hourly load is developed. The two methods selected for final analysis are based on normal and lognormal distribution estimated in a simplified manner. The simplified lognormal estimation method is a new method presented in this thesis. The estimation of several cumulated customer class loads is also analysed. Customer class load estimation which combines the information from load models and distribution network load measurements is developed. This method, called Distribution Load Estimation (DLE), utilises information already available in the utilitys databases and is thus easy to apply. The resulting load data is more reliable than the load models alone. One important result of DLE is the estimate of the customer class share to the distribution systems total load.