Impact of Active Distribution Network on Contingency Analysis of Transmission System

Conventionally, the power system security is ensured through transmission system (TS) contingency analysis. The distribution system (DS) is considered as a fixed aggregated load at the point of connection bus where the quantum of load indicates the power demand of DS from the grid. However, this demand is no longer fixed with the proliferation of renewable energy based distributed generation (DG). The temporal variations associated with the power output of DGs eventually produces uncertainty in the power drawn by a DS from the grid. Thus, any component outage which is not severe may become critical under the instance of sudden increase in load (power demand by DS) and alters the result of contingency analysis (CA). Hence, to prevent missing out alarm signals during such events, the system operators need to communicate with each other for performing security analysis. In this paper, a transmission contingency analysis method has been proposed that considers the impact of active distribution network with exchange of limited data at the point of connection bus between the system operators. To shorten the computation time, criteria for selecting the sensitive load buses is also proposed. Numerical simulations are performed on various test systems to show the impact of uncertainty of renewable energy (RE) based DGs on transmission line flows and bus voltages that can alter the list of critical contingencies.