Research On Distribution Network Line Protection With Inverter Interfaced Distributed Generators

In recent years,with great support from the government,new energy industry represented by wind energy and solar energy has developed rapidly.An increasing of distributed generation has been applied in power grid.The operation mode and control strategy of distributed generation determine the complexity of its fault characteristics.A great deal of distributed generation is applied to the distribution network,which has a great impact on the traditional current protection and grid security of the distribution network.In order to better accept and make full use of renewable energy,and to ensure the safe and reliable operation of the power grid,it is necessary to research the fault characteristics of distributed generation and the distribution network protection with distributed generation.This paper studies the feeder protection of distribution network with distributed generation.The main work and achievements of the thesis include:1.In accordance to the requirements for inverter-interfaced distributed generation by the latest grid-connected standard,inverter-interfaced distributed generation model with low voltage ride through control strategy is built based on PSCAD/MTDC simulation software.In addition,the output characteristics under various fault conditions are analyzed.2.The influence on the distribution network power flow and fault current distribution produced by distributed distributions after being applied in the power grid is studied.In the meanwhile,the application of power current direction component and positive sequence fault directional component in the protection principles of traditional distribution network are applied.The adaptability of the distribution network simulation model based on PSCAD/MTDC software is analyzed.3.Through drawing lessons from pilot impedance protection and using the positive sequence voltage and positive sequence current at both ends of the line,the positive sequence component integrated impedance and positive sequence summation quotient impedance are obtained by symmetric algebraic four-step operation.A new principle of pilot protection based on positive sequence component integrated impedance is proposed.The principle uses the ratio between the difference of two terminals positive sequence voltage phasor of the transmission line and the sum of the two terminals positive sequence currents phasor of the same transmission line to form a positive sequence component Integrated impedance.When the faults occur in outer or internal,the amplitude of the positive sequence component integrated impedance changes obviously.In this way,the internal and outer faults on the line can be distinguished.4.A new principle of pilot protection based on positive sequence summation quotient impedance is proposed.The principle judges faults through utilizing the ratio between the sum of two terminals positive sequence voltage phasor of the transmission line and the sum of two terminals positive sequence current phasor of the same line when fault occurs.When an external fault occurs,the positive sequence summation quotient impedance reflects the capacitance impedance of the line and its value is large.When an internal fault occurs,the ratio ignores the line impedance reflects 2 times the transition resistance or 4 times the transition resistance and its value is relatively small.In this way,the internal and outer faults on the line can be distinguished.Simulative results show that the new principle has obvious characteristics of easy setting,free from the effect of control strategy and the power of the distributed generation,and strong resistance to transition resistance.