Optimal power flow evaluation of distribution network capacity for the connection of distributed generation

Distributed generation capacity will increase significantly as a result of UK Government-led targets and incentives. Whereas the technical problems arising from distribution-level connections may be mitigated for individual connections, the anticipated connection volumes imply a potential risk of conflict between connections, in that inappropriately sized or located plant could constrain further development of the network and consequently threaten the achievement of renewable energy targets. One means of addressing this risk is to encourage development at sites that are more suitable and at the same time discouraging those at inappropriate ones. First of all network operators must be able to evaluate the available capacity on the system (i.e. the headroom). A technique is presented that facilitates such an analysis. Termed 'reverse load-ability', the approach models fixed-power factor distributed generation as negative loads and uses the optimal power flow to perform negative load shedding that effectively maximises capacity and identifies available headroom. The technique is applied to an extensive distribution and subtransmission network. It rapidly identifies available headroom within the imposed thermal and voltage constraints. Furthermore, its use is demonstrated in examining the consequences of a sequence of connections in terms of the impact on available headroom and in sterilising the network.