TRANSIENT STABILITY ENHANCEMENT BY 120-DEGREE PHASE ROTATION.

The concept is to disconnect two generators or two groups of generators when loss of synchronism is imminent (large rotor angle difference due to a fault or other disturbance). The systems are then reclosed with 120-degree phase rotation. Stability can be improved because fast valving, excitation control, or governor control is allowed more time to become effective. The technique is analyzed for radial connection of a fossil-fired steam-turbine unit connected to a large system via long EHV lines and for two large systems with a relatively weak interconnection. For the radial system, the effect of the switching on transient shaft torques and on transient overvoltages is investigated. Also, comparisons with alternate stability enhancement methods are made.