On uncontrolled system separation in power system restoration

Since extended power outages causes severe stress on society and the restoration following a black out is a complex and time consuming task, efficient restoration strategies are needed. During the restoration, the power system undergoes continual changes and therefore it is subject to desired and undesired operations and failures which might be devastating. The main contribution of this paper is a new method to estimate the risk of an uncontrolled system separation in case of a loss of a transmission line or a transformer during a restoration process. The method in this paper assigns failure rates to the transformers and the transmission lines. Further, a graph theoretical method are used to find probability bounds for an uncontrolled system separation for a whole restoration sequence. In a numerical example are three restoration strategies applied to an IEEE 14 bus test system and evaluated. It is shown in the numerical example that the restoration strategy has an high impact on the probability for a system separation.