Investigating the declining reactive power demand of UK distribution networks

The significant decline of reactive power (Q) demand in the UK is considered one of the factors that led in 2011 to over-voltages in the 400kV network. To examine this, a distribution network known to have this decline is modelled in detail (from the transmission interface, 132kV, to 33kV) and validated using monitoring data. In particular, the effects from replacing overhead lines with cables as well as P and Q demand trends (at primary substations) on Q exchanges at the GSP are investigated. Results for this particular distribution network show that high cable penetrations in 132kV circuits lead, during minimum demand, to Q gains many times larger than its 2013 level. In addition, the identified P and Q demand trends at primary substations highlight the future larger Q injections through the transmission interface. These findings can be used to coordinate operational and planning actions between networks operators.