The Protection Method Research For The Distribution Network With Distributed Generation

The contradiction between energy,environmental crisis and economic development is becoming more and more acute,which promotes the rapid development of distributed power generation.A large number of distributed power Grid-connected challenges the protection of distribution network.In this paper,two new protection methods are proposed in view of the impact of distributed power grid connection on distribution network protection.The advantages of the protection method are verified by simulation with MATLAB/Simulink.The influence of distributed generation on current protection in distribution network is analyzed.The steady-state mathematical models of different types of wind turbines and photovoltaic cells are established,and the fault current output characteristics are deduced based on the equivalent circuit.The effects of different grid-connected locations of distributed generators on current protection are compared,and the effects of distributed generators on accelerated protection before reclosure are analyzed.An improved optimal setting method of inverse time overcurrent protection in distribution network is proposed.Taking the minimum total operation time of main protection and backup protection of distribution network as objective function and considering the constraints such as protection selectivity,a mathematical model for optimal setting of inverse time overcurrent protection of distribution network is established.The improved harmony search algorithm is used to solve the problem.By setting dynamic parameters and introducing optimal solution weight,the convergence speed of the algorithm and the ability of obtaining global optimal solution are improved.In order to solve the problem of unsolved protection setting caused by the large difference of short circuit current between different types of faults,two-phase and three-phase short circuit faults are separately optimized off-line,and parameters are automatically matched and optimized in real time according to the type of faults.The correctness and validity of the proposed optimal protection setting model and its solving algorithm are verified by a simulation example of 10 kV distribution system with distributed generation.A protection scheme for distribution network with distributed generation is proposed,which combines current differential protection with over-current protection.Aiming at the difficulty of setting the upstream reverse-time overcurrent protection of distributed generation,the current-to-amplitude ratio differential protection with braking characteristics is configured by means of communication technology,considering the change of the type and operation capacity of distributed generation.In view of the transient steady-state error of current transformer,the braking quantity is quantitatively corrected.In view of the difficulty of taking into account the inter-regional coordination requirements in reverse-time over-current protection,a low-voltage acceleration factor is introduced into upstream protection of distributed power supply.The simulation results show that the protection scheme can effectively improve the operation and coordination characteristics of the protection,and is more economical than the full line differential protection.