Fault Characteristics And Collector Line Protection Within A Large-scale PV Power Station

In recent years,large-scale photovoltaic(PV)power stations are developed rapidly,becoming one of the popular PV generation modes in China.Within a large-scale PV power station,thousands of PV units are collected via cables and overhead lines into the booster substation.Once a fault occurs within the station,the protection’s incorrect operation may lead to the disconnection of the non-fault sections.The protection would cut the whole branch and the true faulted position cannot be pinpointed.Then the fault may be remained for a relative long time and leads to the generation loss.Therefore,there is an urgent need to study on the collector line protection and the fault location within a large-scale PV power station.The study on the collector line protection is based on knowing the PV fault characteristics with the PV station.A detailed model of the PV unit was built to discover fault characteristics under various control strategies.And a consolidated expression for the PV fault current was calculated suitable for variant controls,when considering the fault response of the PV panel.Then,the fault analysis and the built model were verified using the field-testing data.Based on the fault current analysis,the performance of the current differential protection and the current protection of the collector network was evaluated.The weak power feature of the PV would reduce the sensitivity of the current differential protection.The existing current protection experiences mal-operation and mis-operation.To overcome the incorrect coordination of the current protection and distinguish the faulted line from the non-faulted one,a distance protection scheme was proposed on the PV side of the overhead line considering the steady power frequency current from the PV side.The proposed protection scheme enhances the ability of isolating the fault on the overhead lines from the PV side.For the prompt restoration within the station,a new method was proposed to locate the minimum faulted section.The compressive sensing(CS)algorithm is used to solve the undertermined node voltage equations and recover the fault current vector to determine the faulted node.Simulation results indicate that the proposed method can locate the faulted effectively using non-synchronized data from sparse measurements,while considering various fault types,fault resistances and signal noise.The proposed method can help the personnel to clear the fault immediately and then decrease the time consumption for the restoration.