Preventive flow control for transient stability by phase shifting transformers

Interconnections make economic use of the power generated and generally improve overall reliability, but the complexity exists in the power system. Synchronous generators thousands of kilometers apart must operate stably in synchronism even the power transfer conditions such as equipment outages or power disturbance are occurring. If one group of generators accelerates another group, instability and loss of synchronism will be caused. In order to ensure and improve the transmission reliability and capacity against these unexpected accidents, this paper proposes a concept to improve the transmission capacity of the network by phase shifting transformers (PSTs). The concept is, in advance, shifting power flow of the line where an accident is considered to occur to other lines by PSTs. Consequently, the influence of the contingency on the generators can be relieved a lot and operate more stably to prevent from the cascading of failures and the area affected. The effectiveness of the proposal is confirmed through the simulation studies in a three-unit six-bus model system.