Comparing the techniques of defining the synchronous machine load angle

The low-frequency oscillations are natural for power systems and may arise due to both small variations of load and large disturbance. The effect of slight load changes may significantly differ for cases of low-magnitude permanent oscillations, which may be considered acceptable, and unstable oscillations, which may lead to a major system emergency. The existing trend of increasing the capacity of long-range power transmission has led to the situation where inter-area oscillations may appear underdamped or even rising in terms of magnitude. Effective oscillations detection with the corresponding countermeasures along with eliminating the prerequisites leading to the oscillations is a guarantee of minimizing their negative consequences. Therefore, it is of crucial importance to perform continuous monitoring which is to provide the information on the "source" of oscillations – a generator or a group of generators, which do not contribute to the oscillations damping or even support their development. The algorithm of quantitative estimation of synchronous generators participation in low-frequency oscillations damping based on synchronized phasor measurements has been proposed previously. It implies utilizing the concept of synchronizing power as a measure of the capability of the machine to maintain synchronous operation. The load angle of the generator is necessary to define the value of the synchronizing power and since the direct measurement of the load angle is generally not available the techniques of its derivation have been developed. The comparison of these techniques is presented with the estimation of the adopted assumptions effect on the synchronizing power evaluation results.