the demand varies linearly with the voltage. Thanks to a tool that simulates U.K. residential demand (per appliance) and load models for individual appliances available in the literature, the only information required for each primary substation is the number of residential customers and the total peak demand. Despite the fact that the component-based approach is limited to residential customers and depends on other models, it manages to realistically capture the aggregated variability in the demand composition. As shown in Figure 6(b), during early hours of the day, appliances that cool and heat such as space heaters (representing only ~20% of residential Realistic Load Model The Voltage-Demand Relationship Measurement Based Component Based Voltage Capability The Extent to Which the Voltage Can Be Reduced EHV Influence HV Study LV Influence EHV Voltages During Normal Operation Studies on Real HV Networks with LV and EHV Influences Maximum Voltage Reduction Acceptable to Customers Demand Reduction How Much Demand Reduction Can Be Unlocked HV Study Studies on Real HV Networks Considering: * Realistic Load Model * Voltage Capability figure 5. A methodology overview showing how the demand reduction of a given primary substation is quantified. 16 More Light Other Light Wet Heating and Cooking Electronic More Electronics Cold 14 Primary Substation (Hundreds of Secondary Substation) Demand (MW) 12 Secondary Substation (Hundreds of Houses) House (Dozens of Appliances) 10 8 More Heaters 6 4 2 Appliance 0 00:00 (a) 1.3 06:00 09:00 12:00 15:00 Time (hh:mm), 24 h (b) More Responsive (More Heaters) 1.2 Load Model-np 03:00 18:00 21:00 More Responsive (More Light) 1.1 1.0 0.9 Less Responsive (More Electronics) 0.8 0.7 00:00 03:00 06:00 09:00 12:00 15:00 Time (hh:mm), 24 h (c) 18:00 21:00 figure 6. (a) An overview of the component-based approach, (b) the estimated primary substation demand with breakdown per appliance type, and (c) the estimated time-varying load model for the same primary substation. may/june 2017 ieee power & energy magazine 59