Research On Relay Protection Technology Of Distributed Network With Distributed Generator

Distributed Generators(DG)mainly include photovoltaic power generation,wind power generation and other renewable clean energy,which have obvious randomness and intermittency.Power supply structure and trend direction of power grid are changed with DG accessing to distribution network,and a series of problems such as rejection,maloperation,desensitization,and automatic reclosing failure in original relay protection device are found.Therefore,it is of great significance to study the influence of distributed generator accessed to distributed network on the original relay protection configuration and design a new protection scheme.Firstly,the power supply structure,working principle,control strategy and fault characteristics of Inverter Interfaced Distributed Generator(IIDG)are elaborated,and models of HDG with constant power control in PSCAD/EMTDC simulation software are built.Secondly,the three-phase current and automatic reclosing protection of the traditional distribution network are analyzed in principle.The influence of relay protection of the distribution network is analyzed theoretically from the different fault position,the changeable IIDG capacity and so forth with IIDG accessing to the distribution network,and the 10kV distribution network system with IIDG in Jining area is simulated and analyzed in the PSCAD/EMTDC environment.The simulation results show that the traditional protection configuration cannot meet the requirements of the new power supply structure with IIDG distribution network.In order to meet the new requirements of relay protection,an improved adaptive current quick-break protection scheme and an improved three-stage current protection scheme are designed.The improved adaptive current quick-break protection can reflect the voltage and current value of the protection device in real time and can be adjusted online.The improved three-phase current protection scheme takes the access capacity of the IIDG into account and sets it as one of protection setting condition to adjust offline.Finally,the two protection schemes are simulated and analyzed in PSCAD/EMTDC environment.The simulation results show that the relay protection devices can operate reliably and have better selectivity and sensitivity to ensure the safe operation of power system with different IIDG grid capacity,different fault type and location of relay protection device.