A Congestion Alleviation Technique Exploiting Structural Insights on the Interaction of Line Loading Limits, Reactance and Line Outage Security Constraints

Line outage security constraints ensure that a proposed generating schedule will not load any line to the point where its removal causes more overloading elsewhere. These security constraints increase operating costs by occasionally precluding the usage of the cheapest generation sources. That is, power networks frequently suffer congestion in this (N-1) sense. To explore the structural origins of such (N-1) congestion, this paper defines a new metric for branches within a grid, shadow capacity, which gauges the maximum flow on a branch before its removal would tend to overload other lines elsewhere. Using this novel metric, we argue the (N-1) congestion is a consequence of imbalances in the pattern of line reactances and capacities across a network. To further explore the insights offered by the shadow capacity analysis, a novel methodology to relieve (N-1) congestion and hence improve the grid's loadability is developed. This technique adds fixed reactance to certain lines in the grid to boost their shadow capacities. These results show modest alleviation of actual (N-1) congestion, which shows the potential value of optimising power networks through the lens of shadow capacity enhancement.