Forecasting is simply a systematic procedure for quantitatively defining future loads. Depending on the time period of interest, a specific forecasting procedure may be classified as a short term, intermediate, or long term technique,
Because system planning is our basic concern and because planning for the flew generation, transmission and distribution facilities must begin 4 - 10 year in advance of the actual in service data, we shall be concerned with the methodology of intermediate-range forecasting.
For simplicity, the word “Forecast” will usually imply an intermediate range forecast.
Forecasting techniques may be divided into 3 broad classes. Techniques may be used on extrapolation or correlation or a combination of both. Techniques may be further classified as deterministic, probabilistic, or stochastic.
a) Extrapolation
Extrapolation techniques involve fitting trend curves to basic historical data adjusted to reflect the growth. It produces reasonable results in many cases.
Such a technique is to be classified as a deterministic extrapolation, since no attempt is made to account for random errors in the data or in the analytical model. Some standard analytical functions are used in trend curves fitting, including:
1. Straight line
2. Parabola
The most common curve - fitting technique for finding coefficients of function in a given forecast is the method of least squares as will be discussed later
b) Correlation
Correlation techniques are used to relate system loads to various demographic and economic factors. This approach has an advantage of forcing the forecast to understand clearly the interrelationship between load growth patterns and other measurable factors. The most obvious disadvantage, however results from the need to forecast demographic and economic factors, which can be more difficult than forecasting system load. Typically, these factors may be population, employment, building permits saturation and business indicators.
No comments:
Post a Comment