Voltage Sag Optimal Monitors Allocation Method And Fault Location Estimation

As the construction of smart grid and the concern on power qualtiy, power grid companies are actively promoting the construction of power quality monitoring system (PQMS), which can real-time monitor the power quality of whole gird. Voltage sag is one of the most serious problems affecting power quality. There is a vital need to deal with the large amount of data extracted from PQMS. Voltage sag is mostly caused by faults in power system, propagates through the system and affects loads far away from the fault location. Therefore, estimating the fault location of voltage sag and evaluating the area influenced by voltage sag are of great significance. It can help distinguish the responsibilities between power suppliers and consumers, analyze the influence of voltage sag, provide reliable data for safety accident investigation and economic loss estimation, as well as help the customer service center to respond quickly.Firstly, this paper proposes different voltage sag analysis methods respectively based on the characteristics of transmission network and distribution network, then programs these two methods in MATLAB. The simulating results in different types of fault show the effectiveness of proposed methods.Considering the propagation rules of voltage sag in power grid, this paper proposes the method of optimal monitors allocation based on power grid partition, and comes up with the partition principle and nest-loop partition algorithm. Bus-MRA (monitor reach area) matrix and line-MRA matrix are defined to maintains the continuity of lines, which is more reasonable. The improved allocation method is realized by MATLAB and simulated in PSCAD.The results verify the correctness and feasibility of proposed mthod.Fault location is not a new issue on power system research. Traditional fault location methods can be classified in two categories:one is obtaining the relative position (upstream or downstream) of the fault for a given monitor, the other is to get the exact fault location by multi-search criteria or intelligent algorithm. The formmer can not get the exact location of fault, while the latter mostly ignores the influence of fault resistance and calls for high requirements of the allocation of PQMS. Therefore, this paper proposed a novel fault location estimation method for voltage sag, which is based on the improved optimal monitors allocation. By this method, fault position and fault resistance can be estimated by particle swarm optimization algorithm (PSO). Multi-source information fusion is used, to narrow the search area of fault location and improve efficiency and accuracy of proposed method. Based on the location result, voltage sag influence area can be analyzed.Finally, two examples are given to demonstrate the availability and accuracy of proposed method in MATLAB. The 560-bus practical example shows the accuracy and practicability of proposed fault location estimation method. The IEEE 33-bus system example results show that improving the measurement accuracy is more effective than by increasing the number of PQ monitors, in order to promote the location estimation accuracy. Therefore, if economic conditions permit, choosing the monitoring device with high measurement accuracy is a better choice.