Design and development of wide area protection and emergency control for application in distribution networks of embeded generation

The design and development of a wide area protection and emergency control system for application in distribution networks of embedded generation is presented in this paper. The system developed consists of a central unit, and one local unit at each substation of a distribution network. It integrates the functions of monitoring, protection and control. The main control function of the system is to detect whether there is any distribution network islanded from main grid after a power system fault. If it is islanded, as there are embedded generations in the islanded area, the frequency will shift from 50Hz. The system can shed load or trip excess generations to maintain the frequency near 50 Hz to keep the islanded area running, also to meet the synch check criteria for auto-closing an alternative grid standby supply. The system monitors the real time information of currents, voltage and power of each circuit in the distribution network, also the topology of the network, it can make optimum decision for load shedding or generation tripping based on real time information of power flow of each circuit. With this system, the CB of the alternative standby grid supply can be auto-closed and grid supply can be restored to the islanded area quickly (less than 10s). Compared to the traditional control schemes (10 or 20 minutes restoration time), the new system will improve the supply reliability significantly. The system was installed in a distribution network of six 110 kV substations in October 2013, so far its performance is satisfactory.