A new protection scheme based on distributed decision in smart distribution grid

With the development of smart distribution network, the distribution system is introduced with a large number of distributed generations (DGs). It becomes an active network that both the load and fault currents flow two-way, which leads to serious impacts on the protection's selectivity and sensitivity. In this paper, by analyzing current characteristics of a typical distribution network with DGs, a new distributed decision protection method which combines traditional over-current scheme and distributed wide-area protection is proposed. In this method, each line needs to install a smart terminal unit (STU) which obtains local data of current amplitude and direction in real time and processes them into logical values used to realize a specified logical operation. According to local and adjacent STU's calculation results, STUs can judge the fault area without synchronous sampling and isolate the fault by controlling the local protective devices accurately and quickly.