Analysis and mitigation countermeasures of a new SSO phenomenon

In Inner Mongolia of China, the generators in several power plants are experiencing a new subsynchronous interaction problem. It belongs to subsynchronous torsional interaction (SSTI) between the generators and HVDC, but has many different characteristics from conventional SSTI. This paper describes the different characteristics according to the actual recording. Preliminary analysis is made for the root cause as well as the probable disturbance source. PSCAD/EMTDC is used to build up equivalent model of the power system and complex torque coefficient approach is utilized to scan the electrical damping characteristics of the system. A stimulation method is presented to simulate the similar disturbance as actual condition. The feasibilities of several mitigation countermeasures are analysed in detail and finally the countermeasure that STATCOM at the generator terminal is recommended.