A method of determining remedial control actions for a power system in an insecure and unstable operating condition is provided. The power system has a plurality of generators injecting power into a network and each generator has a generator injection impedance and a stability boundary in the injection impedance plane. A system safety boundary is calculated based on a predetermined network operating safety margin for each generator, the generator injection impedance is compared with the safety boundary and it is determined whether each generator is safe or unsafe. A remedial control action is determined comprising a scheme for re-dispatching power generation for each unsafe generator to thereby establish a secure operating condition for the power system.A new safe operating point in the impedance plane for each unsafe generator may be determined, and a distance between the generator injection impedance and the new safe operating point is calculated under the assumption of constant voltage magnitude for each unsafe generator. The unsafe generator operation is remedied by reducing power generation of the unsafe generator.