An Online Measurement Approach of Generators’ Torsional Mechanical Damping Coefficients for Subsynchronous Oscillation Analysis

The series compensation capacitor and HVDC are widely used in Chinese power grids to increase the transmission capability of long distance lines, which might cause subsynchronous oscillation (SSO) between the turbine generators and power systems. The torsional mechanical damping coefficient of a turbine generator reflects the inherent damping level of the shaft and, thus, is a critical factor in SSO analysis. However, the torsional mechanical damping coefficient under practical operating conditions is difficult to obtain from the design parameters. In this paper, a novel approach is developed for online torsional mechanical damping coefficient measurements. The torsional interaction mechanism of identical parallel connected turbine generators is investigated, and then the characteristics of in-phase mode (IPM) and anti-phase mode (APM) are described. From this analysis, an active stimulating method for APM is presented, and a practical scheme for online torsional mechanical damping coefficient measurement is designed. This approach takes advantage of the APM features and decouples the generators from the grid. Moreover, the proposed approach has been implemented in the Yimin power plant in Inner Mongolia to realize online measurement of the torsional mechanical damping coefficient. Field test results are presented to demonstrate the effectiveness of the proposed approach.