Computing Dynamic Instability of a Power System after Relay Failures

This paper discusses analyses of power system instability due to relay failures related to grid faults. Different power systems differ significantly in their response to a disturbance and in their behavior in disturbed conditions. Therefore, the vulnerability of the system also to relay misoperations is highly case-dependent. When stability is the issue, a system breakdown most probably occurs when fault duration is extended or when several components trip unselectively, which both can lead to an unstable condition. When considering the method for evaluating the power system consequences of disturbances, a steady-state approach is not sufficient for systems limited by dynamic stability criteria. In these cases, system wide dynamic simulations are needed. This paper describes the dynamic simulations of the Nordic power system after relay failures and concludes that the frequency of a system breakdown differs significantly according to the direction and amount of power transmission.