Modelling the short-term and long-term aggregate response of multiple loads fed through a sub-transmission network

This paper addresses the problem of representing the aggregate response to voltage changes of a set of loads fed through distribution transformers connected by a sub-transmission network. A simple, while accurate equivalent is proposed. The latter involves standard network components and includes a single internal bus. This equivalent matches both the short-term and the long-term response of the original system, the long-term dynamics coming from the load tap changers that control the distribution voltages. A procedure to identify its parameters from step responses of unreduced system is detailed. The method is illustrated and validated on a large sub-transmission-distribution system of Hydro-Quebec