Distributed Regional Longitudinal Protection And Power Restoration System Studies For Smart Distribution Grid

Smart distribution grid is more secure and reliable than traditional distributed grid because it integrates advanced distribution technology, advanced sensor measurement, control technology, and supports many distributed generations. It requires the protection system to isolate the fault and restore power supply rapidly. However, with so many distributed generations connected to distributed grid, the structure of traditional distribution grid and power flow direction changed. The protection may fail to operate because the connection of distributed generation to the system changes the fault current direction and magnitude. Hence the traditional protection can’t meet the requirements of smart distribution grid. Therefore, it is necessary to propose a new fault isolation algorithm. Additionally, the system should not isolate the distributed generation immediately when there is a fault in distribution grid because it is harmful to the stability of system. In this paper, based on the requirements of fault isolation and power restoration in smart distribution grid, the research on isolation and recovery are studied. The concrete research content is as following.Firstly, based on previous research and considering features of smart distribution grid, this paper put the pilot protection which is widely used in transmission network into use in smart distribution grid form a distributed regional longitudinal protection system. Owning to the complex structure of smart distribution grid, the pilot protection can’t be used directly in smart distribution grid. We should deal with several key issues to adapt distribution grid structure, such as the smart distribution terminal unit should communicate with which smart distribution terminal unit, and communicate which the type information.This paper solves the first issue using matrix calculation method to determine the associated area for every smart distribution terminal unit. The protection host computer make use of technology structure information to determine every smart distribution terminal unit needs communicate with which units and send results to every unit. Then smart distribution terminal unit can complete the function of isolate fault independently. This stytem combine advantages of centralize and distributed structure, so it operate quickly. The information which smart distribution terminal unit communicates with each other included fault direction information and over-current information to improve the fault tolerance and reduce unnecessary calculation. This paper presents a modified principle of over-current protection which can response this line and next adjacent line short-circuit fault. Finally, a fault isolation algorithm of distributed regional longitudinal is given in this paper using logical operation to isolate the fault.Secondly, the structure of smart distribution grid is more complex, it is necessary to get the sequence of switches to recover the power for users to reduce the economic loss. Based on multi-agent technology application in power restoration, this paper presents a distribution power restoration which calculate faster but the result is not the best for the system. Since this method doesn’t need the control host computer collect information, smart distribution terminal unit can finish recovering power function independently, this method is faster than traditional. After fault isolation, the system first islanding and the smart distribution terminal unit in non-fault power supply interrupted district as a starting point hunting routes of power recorvey. After knowing all routes, the smart distribution terminal unit which connectted to interconnection switch communicates with their associated area to decide the size of recovery area.