Reactive Power - Voltage Nodal Controller for Integration of Windfarm Clusters Connected to the Distribution Grid

The System Non-Synchronous Penetration (SNSP) level for the Irish power grid is currently limited to 60 %. It is intended that this will ultimately be increased to 75 % which is related to achieving Ireland’s EU 2020 targets for electricity from renewable energy sources. Thus, at times, up to 75 % of the instantaneous power demand will be supplied from non-synchronous energy sources. This poses many engineering and technical challenges for the Irish power system. One such challenge is the shortfall of reactive power which is needed to manage the voltage levels on the power grid. A high wind dispatch means less conventional power plants on the system, which would otherwise have been a source of reactive power support. To the extent that it makes sufficient engineering sense to do so, some windfarms should contribute to this shortfall. Topology and electrical distance from the TSO-DSO boundary heavily influence whether and to what extent the reactive power capabilities of distributed energy resources should be used for local voltage optimisation or offer a degree of support to the transmission system. For a designated subset of windfarms a control technology is needed to allow ESB Networks as the licenced distribution system operator in Ireland to utilise the reactive power capability to provide voltage support to the transmission system. A reactive power - voltage device, called a nodal controller, is described in this paper. It allows reactive power to flow safely through the distribution network while maintaining safe distribution system voltages and currents. The nodal controller is a radically new concept and seeks, for identified types of larger windfarms, to use centralised and automated intelligence to allow as much reactive power support as possible to be delivered to the TSO-DSO interface whilst at the same time respecting voltage and thermal limits on the distribution network. The architecture and operation of the nodal controller for windfarm clusters are presented. The nodal controller uses a novel computational method that controls the reactive power generation of the connected windfarms and voltage of the 110 kV / 38 kV (or MV) transformer to endeavour to meet the reactive power / voltage set-points at the TSO-DSO interface. The proposed reactive power - voltage nodal controller was modelled and tested in a simulation environment using a part of the distribution system model. The simulation results are presented. A trial installation is under implementation at Cauteen windfarm cluster in County Tipperary, Ireland. It is anticipated that once the concept is proven operationally it will be implemented to more windfarms across Ireland.