The application of synchronous grid connection in power supply system

When large power supply system becomes isolated after fault occurred, the best method is finding a suitable grid-connected point to connect with external power system to maintain stable. This paper presents different connection methods on different operation conditions based on one actual power supply system. If active power in isolated system is larger than load demand, cutting-generator is adopted; if less, low-frequency load shedding is adopted to keep system stable firstly, then synchronous connection conditions are checked to connect isolated system with external power system in steady state. This connection method is safe and reliable. When there are fewer generators in isolated supply system, stability can´t be remained by load shedding, it is necessary to rapidly connect with external power grid in order to remain power supply stable, this time grid connection must be conducted in transient state. In this situation connection conditions are decided mainly by phase and frequency difference. This rapid connection method is analyzed and verified, and connection conditions are derived by calculation.