Introduction: In the last 2 years, there have been significant difficulties in managing voltage levels during minimum demand periods. Analysis of this issue has shown that the root cause is likely to be related to the significant decline in reactive power relative to active power. Whilst minimum active power demands have fallen by around 15% in the last 5 years, reactive power has declined by 50% in this time. Current trends for 2012 show that this reduction is continuing, broadly, across the country. In order to better understand the challenge of managing voltage levels within limits and to plan for additional future reactive compensation requirements, a thorough understanding of the reactive power trend needs to be developed. A previous paper has highlighted some possible causes such as embedded generation growth, increasing use of energy efficient equipment and impact of austerity measures (e.g. reduced use of street lighting). Further work on these and other potential causes (e.g.combined heat and power, electric vehicles) is required.

Objectives: The key objectives are to determine:

a) The factors behind the significant decline in reactive power demand and increase in the distribution network operator (DNO) system reactive power gain as observed at the Transmission/ DNO interface during periods of minimum daily demand observed over the last 5 years

b) Its relationship to the overall decline in active power at these interfaces during these periods.

Having looked at these factors, the project should then determine the most likely trends for reactive power in future years and produce a report providing forecast scenarios for the active and reactive power at these DNO supply interfaces. The assessment of the decline should attempt to identify how far the trend will decline (and at what point a “floor” might be reached) of reactive power exchange to the power system that might be expected overnight. Against this floor, further case study evaluation of the response of the network under such stressed conditions overvoltage disturbances (e.g. failure of a shunt reactor or major provider of reactive power absorption) is to be used to determine minimum pre- fault levels of voltage profiles available to be adopted to prevent insulation breakdown and other modes of cascade failure emerging.

The project will need the Energy Networks Asssociation (ENA) and DNO engagement with the university project. The later stage of the project is more transmission network focussed. Network gain should be broken down into the fixed component of the transmission network - DNO interface mentioned above, the loading of the transmission system at the time, and the inherent characteristics of that network {susceptance, saturation characteristics, controller & protection response} so as to improve understanding across these areas.