A discussion of reactive power control possibilities in distribution networks dedicated to generation

There are various control modes available for the reactive power behaviour of modern wind farms. Using a simple scoping load-flow simulation approach, this paper discusses some of the various interactions that may arise between wind farm and transformer voltage regulators. For two sample generation-only distribution networks, a load-flow calculation was run for every minute of a test month, updating wind outputs each period, and imposing the historic transmission system voltage at the appropriate bus. This fine-grained approach, simple as it is, allows some separation of the control effects of slow-acting tap changers at bulk supply transformers, and fast-acting power electronics in wind farms. For three categories of control scheme - local voltage control, power factor control, and active control - the performance of each wind cluster is quantified from the perspective of the transmission and distribution system operator. Information relevant to the transmission system operator is the aggregate response of the wind cluster: how does the net reactive power flow vary with system voltage and with wind power exports? For the distribution system operator, the effects of the various control modes on active power losses and transformer tapping activity is explicitly captured. This simulation approach, while not rigorous or definitive, does draw out some salient relationships and gives a useful basis for discussion of reactive power control possibilities.