Synchronous and Asynchronous Generators Frequency and Harmonics Behavior after a Sudden Load Rejection

This paper describes load rejection tests done at two hydro power plants in Sweden, one equipped with synchronous and the other with asynchronous generators. During the tests, voltages and currents are digitized, recorded, and thereafter offline processed. By this, in the processing of distorted and fast parameter-varying voltages and currents, the powerful estimation technique, the Newton type algorithm, is applied. It was intended to investigate the frequency changes and the distortions of the measured signals. The transient processes at both generators are compared. In particular, the frequency changes after the instance of load rejection are investigated and discussed from the signal processing and physical nature point of view.