Market Equilibrium in Congested Transmission Networks with Transformer Tap-Ratio Control

In this paper, the impact of transformer tap-ratio control on the electricity market equilibrium in congested transmission networks is investigated. The analysis is performed using a primal-dual nonlinear interior point algorithm for determining the Nash Supply Function Equilibrium (SFE) of bid-based electricity markets, formulated using ac network model representation. Numerical results demonstrate the effect of tap-ratio control on the bidding strategies of the generating firms for different cases of transmission line congestion conditions, with direct impact on nodal prices and profits. The results show that the impact of the transformer tap-ratio control on the market equilibrium depends on the degree of transmission line congestion in the network.