Extended Ward equivalent of external system for on-line security analysis

Today´s power systems are more and more intensively interconnected. The monitored part of the power system that these measurements cover normally consists of the energy control centre´s own system which is called the internal system, and the neighbouring system which is called the external system. Usually, the external system is far bigger than the internal system and a modern energy control centre for a number of the interconnections is responsible for the control of the internal system. So external network modelling is becoming an important component of on-line security analysis. This paper investigates the extended Ward equivalent method. A new equivalent modelling, with sparsity technique, for on-line power system security analysis is presented. The extended Ward equivalent has been tested by simulation on the IEEE 30-bus, IEEE 118-bus load flow test system, and the 706-bus interconnected power system of the NGC. The results show that extended Ward equivalent has suitable properties for practical use and further development