Research On Fault Analysis And Relay Protection On Distribution Networks With Distributed Photovoltaic Generators

Due to the characteristics of distributed photovoltaic(PV)are different from the synchronous machine,the conventional fault analysis methods are not suitable in distribution networks.What’s more,the sensitivity,selectivity,and reliability of the line relay protection are affected by the PV connection,it is necessary to extend the fault analysis and line protection methods.This thesis studied the fault analysis and line relay protection in distribution networks with PV connection.The following works were investigated in this thesis.1)A new fault analysis method was proposed for distribution networks connected with PV in this thesis.The backward/forward sweep(BFS)method was improved and used to estimate the normal and fault voltage components in the proposed method.To calculate fault currents in meshed networks,the multiport equivalent compensation method was utilized in the looped systems.The new method can obtain results without using the node impedance matrix and the calculation time was less than the conventional methods,which can be used in radial and weakly meshed distribution networks with PV connection.2)A phase domain fault analysis method for unbalanced systems connected with PV was developed in this thesis.The proposed method improved and extended a canonical analysis method in phase domain to analyze faults occurring at any position of the faulty line,considering the network characteristics and PV control strategy.In comparison with the existing fault analysis methods,the new method can analyze fault with a better adaptability and generality.3)A new inverse-time distance(ITD)protection for distribution networks with PV connection was proposed in this thesis,based on analyzing the effect of PV connection on relay protection.The proposed scheme used the inverse-time characteristics to set the operating time,which can meet the FRT requirements of PV as well as the selectivity of feeder protection system.To mitigate the fault resistance and infeed effect on the measured impedance,a method was developed,based on transmitting signals between adjacent relays.The aforementioned methods and scheme can extend the fault analysis and relay protection methods.