Principle And Simulation Research Of Relay Protection Based On Micro PMU For Active Distribution Network

With the gradual depletion of fossil energy and the increasingly serious environmental problems in the world,Distributed Generator(DG),has rapid development as a clean and sustainable alternative to energy.Large numbers of DGs like wind and photovoltaic,etc.are integrated into distribution network,which brings great challenges to the safe operation and the relay protection scheme of conventional distribution network.In this paper,a distribution network integrated DGs are simulated in DIgSILENT and the impacts of the DG integration on the conventional relay protection are analyzed.Additionally,three protection schemes suitable for the distribution network with DGs are proposed based PMU(Phasor Measurement Unit).DIgSILENT plays an important role in the simulation of relay protection due to its accurate modeling of DG and the way to layered modeling of relay protection schemes.In this work,relay protection modeling,simulation principle and modeling architecture in DIgSILENT are investigated.By using the relay protection function modules,models of over-current protection and distance protection is established.The built models are verified by fault event simulated in DIgSILENT.Meanwhile,the impacts of DG integration on conventional over-current protection and distance protection are analyzed,and the effects on two protections are compared.It is concluded that distance protection is less sensitive to DG and the conclusion is validated by simulations.PMU enables real-time and simultaneous measurement of the operating status of the distribution system.As the conventional fails to meet the demand of the distribution network with DG,a protection scheme for distribution network integrated DG is presented based on the characteristics of the difference between two phases of incoming and outgoing currents on the bus.In order to overcome the shortcomings of the conventional longitudinal protection,the positive sequence fault components are introduced.The effects of the high impedance faults on the conventional longitudinal protection are reduced by the differential current protection and the phase differential protection.The method is verified with simulation results.