The redistribution of power flow in cascading failures

Understanding the redistribution of power flow is crucial to understanding the dynamics of cascading failures. Such redistribution is complicated, with monotonicity being the exception rather than the norm. We study the monotonicity of a quadratic function of branch power flow with respect to link failure and load shedding, respectively. The quadratic function can be considered as a measure of the aggregate network loading. We show that the value of this measure increases when (more) link failure occurs. On the other hand, while arbitrary load shedding can increase the measure value, we establish the existence of load shedding that can guarantee its reduction. Utilizing these monotonicity properties, we show that the failure of a link will cause the power flow over its adjacent link to have a change in the same direction (away or towards their commonly incident bus) as the original flow over the failed link.