**Long Term Load Forecasting in Power System:**

Long Term Load Forecasting – If the load forecasts are required for planning purposes, it is necessary to select the lead time to lie in the range of a few months to a few years. In such cases, the load demand should be decomposed in a manner that reflects the dependence of the load on the various segments of the economy of the concerned region. For example, the total load demand y(k) may be decomposed as

where a_{i} are the regression coefficients, y_{i}(k) are the chosen economic variables and e(k) represents the error of modelling. A relatively simple procedure is to rewrite the model equation in the familiar vector notation

where

The regression coefficients may then be estimated using the convenient least squares algorithm. The load forecasts are then possible through the simple relation

where x̂(k) is the estimate of the coefficient vector based on the data available till the kth sampling point and ĥ(k + 1/k) is the one-step-ahead prediction of the regression vector h(k).

**Reactive Load Forecast:**

Reactive loads are not easy to forecast as compared to active loads, since reactive loads are made up of not only reactive components of loads, but also of transmission and distribution networks and compensating VAR devices such as SVC, FACTs etc. Therefore, past data may not yield the correct forecast as reactive load varies with variations in network configuration during varying operating conditions. Use of active load forecast with power factor prediction may result in somewhat satisfactory results. Of course, here also, only very recent past data (few minutes/hours) may be used, thus assuming steady-state network configuration. Forecasted reactive loads are adapted with current reactive requirements of network including var compensation devices. Such forecasts are needed for security analysis, voltage/reactive power scheduling etc. If control action is insufficient, structural modifications have to be carried out, i.e., new generating units, new lines or new var compensating devices normally have to be installed.