Voltage Support from Distribution Level Resources in South-East England

This paper demonstrates the effectiveness of distribution level (≤132 kV) resources to tackle the voltage problem at the 400 kV transmission system in the south-east of England. Such voltage problem is a major concern for the UK transmission system operator, National Grid, and is set to aggravate once Dungeness, the only synchronous power plant in the region, is decommissioned. Aggregate reactive power capability of the grid interface converters of distributed generation (DG) in the region is shown to mitigate both under- and over-voltage problems. Tap-stagger operation of the 132/33 kV parallel transformers is also exploited in the over-voltage case. Critical double-circuit outages in the 400 kV network and a range of credible import-export conditions through the HVDC interconnectors to Europe are considered to assess the capability of the distribution level resources to support the voltage at 400 kV level. Representative dynamic models of the 400 kV transmission system from National Grid and 132-33 kV distribution network from UK Power Networks are used in this study to reflect the actual problem as closely as possible.