Adaptive Distance Protection Of PV Grid-Tied Transmission Lines

As the trend of power generation from renewable resources continues to grow,the increasing installation of grid-connected PV systems,which is closely connected to the loads and has little effect on the electric power grid,is considered as one of the major issues that faces the expansion of PV power systems globally,especially large-scale centralized systems,which may bring new problems to the traditional sectors such as conventional protection system.Distance protection is general power transmission and sub-transmission network line protection.Short circuit current contributed from the photovoltaic(PV)power system is depends on type of inverters and the inverter control strategy,and limited by the grid inverter,with the current superposition of conventional power system supply,the fault location and measurement of conventional distance protection relay have an impact.It is also an urgent problem to study the characteristics and setting methods of protection for power transmission line connected photovoltaic power stations.This thesis deals with the lines protection of the electric power grid that photovoltaic power system integrated with,it analyses the influence of the grid connected photovoltaic system on the conventional distance relays.The weak infeed from the PV system and the existence of the fault resistance leads the measured impedance in the conventional distance protection to be increasingly inaccurate and mislead.Another problem PV connected grid is that the variant values of impedance due to the changing in the power level of PV system.The impact of resistance fault on relay operation for transmission lines included PV power plant has been analyzed for faults at different locations and fault resistance values,generating new relay tripping zone of distance protection is proposed to tackle this impact.A new adaptive distance protection zone was proposed and built in MATLAB\Simulink.The problem of variant values of impedance due to the changing in the power level of PV system(at 100%,at 80%)of the PV rated power has been solved by using the new proposed adaptive distance relay.The new zone has been checked and simulated.The analysis was carried out on 33-kV transmission line including PV power system on the first side and power grid on the other.