Capability Assessment of Distribution Network Reactive Power Supports for Transmission Network Using Linear Estimation

Transmission System Operators (TSOs) are currently experiencing a voltage rise problem on their network, especially during the periods of low demands. It is costly to mitigate the excessive voltages by installing reactors or Var compensators in transmission network. Recently, an alternative method of utilising the existing parallel transformers of distribution network is proposed. It uses a tap stagger technique, to address this problem. This paper investigates the VAr support capability of the tap stagger technique with the method of linear estimation. Two real different-sized subdistribution networks are modelled and their load flow results with the tap stagger operation are studied. Then the capability for the whole distribution network is estimated by the linear estimation method. The results indicate the capability is high and show the potential to provide sufficient reactive power services to transmission systems.