This paper first outlines developments over the past 25 years in hourly modeling of native load supplied by Hydro-Quebec. A brief description is then given of the forecasting models used, their performance and derived applications. Beyond hourly forecasting of Quebec demand, these models are used to compute the hourly Np factor, week-ahead probabilistic forecasts, and statistics on normalized energy consumption and peak load. The potential over those 25 years for using analytical model developments is shown. Frequent tuning of model parameters and adjustment to new load contexts ensure that forecasts and derived products are of high quality.

This paper deals with the simulation of long-term responses of power systems to large disturbances in the presence of discrete events. After outlining the power system model under the quasi steady-state (QSS) approximation, a method combining detailed and QSS time simulations is presented, the former being used for accuracy and the latter for efficiency reasons. Detailed time simulation is used to analyze the short-term period following a large disturbance and identify the discrete controls triggered. Next, QSS simulation is used to simulate the same time interval with the discrete controls imposed as external events, before letting the system evolve as usual in the long-term. This simple method has been successfully tested on the Hydro-Québec system.

The quasi steady-state (QSS) approximation of long-term dynamics relies on time-scale decomposition and consists of replacing faster phenomena by their equilibrium conditions, in order to reduce the complexity of the whole model and increase the computation efficiency of time simulations. This paper describes the extension of a QSS model extensively used in long-term voltage stability studies, to readily incorporate the frequency dynamics that takes place over the same time scale. This extended QSS model relies on a common-frequency assumption. Its advantages, limitations and possible improvements are discussed through simulation results on the hydro-Quebec system, where it has been compared to full time scale simulations. Disturbances with an impact on either frequency or voltages are considered and the coupling between these two aspects of long-term dynamics is briefly discussed.