A comparative analysis of power system transient stability assessment by direct and hybrid methods

The paper presents the fundamental differences between two different approaches in transient stability assessment for electric power systems: time domain simulation and direct methods which make use of transient energy functions (TEF). After having examined the most significant advantages and drawbacks of the above approaches, the paper reports the features of the so-called hybrid methods, i.e. stability assessment tools based on simulation and on TEF concepts, which are expected to benefit the advantages of both methods. Results of a preliminary comparative analysis among the different approaches carried out on a test system are reported. Some comments in view of applications of hybrid and direct methods for on-line security assessment are expressed.