Introduction: It has been some time since the modelling assumptions underlying current composite demand models have been challenged with respect to voltage sensitivity. During this time the types of loads, and their performance characteristics, have changed, meaning that currently used models may not be representative. A number of important system planning and operational tasks (including voltage stability and the identification of initial conditions for fault level studies) would benefit greatly from revised models with improved representations of Voltage Dependency of Load (VDL). This project will consider quasi-steady-state modelling only. Through liaison with DNOs it will improve the understanding of the composition of loads currently connected to the transmission system and develop updated models for use in system analysis studies to represent

Objectives: The project will investigate the composition of loads connected to DNO networks, evaluate the current load models used in analysis work, and, if appropriate, recommend updated models. The project will undertake some validation of the models by comparing study results using them with measurements taken during large system voltage disturbances.

There will be two deliverables:

• A report describing revised composite load models applicable for the UK and indicating their impact within load flow studies in relation to VDL

• A report documenting the comparison of measured responses against a theoretical model based on current assumptions.