Research On Optical Differential Protection Criterion And Dynamic Model Test

Relay protection is the key to ensure the security of power system and it is the most effective way to ensure the security and stability of the system.Based on the principle of Kirchhoff,current differential protection is widely used as a main protection to transformers,transmission lines and bus and other components because of its simple principle,short operation time and high reliability.At present,the current differential protection is mostly based on the traditional electromagnetic transformer,but the transient performance of electromagnetic transformer can be reduced due to the magnetic saturation caused by decaying DC component in power system fault.In addition,the Fourier transform of the whole frequency or half cycle of the current power frequency as the differential protection criterion makes the operation speed of protection relatively fast.In order to better adapt to the development of modern smart grid,make the relay protection of the rapid and reliable performance superior,the study of optical based differential protection has become particularly important.Optical differential protection uses optical current transformer and optical protection device realize the action criterion of differential protection and it is a new concept of relay protection in power system.This paper is based on the project "research on improving the whole group action time based on the new principle of optical relay protection" and research the sensing principle of optical current transformer and the action criterion of optical differential protection.Based on the analysis of the integral time window in the protection criterion,a reasonable time window is obtained,which has good selectivity and high speed.Based on the analysis of the braking coefficient of the protection criterion,the suitable range of the braking coefficient is obtained.The effect of frequency offset on the braking ratio of out of area fault is analyzed.Through the Matlab/Simulink software on both ends of the power transmission line modeling and simulation,comparative analysis of the conventional differential protection with optical differential protection when external fault brake ratio characteristics,sensitivity analysis and transition resistance under different protection.Finally,the scheme of double terminal optical differential protection is proposed,and a real-time simulation model of the system is built on RTDS.A complete closed circuit protection test system is established by connecting with the twice protection equipment,thus the functional test of the prototype of the optical differential line protection principle is carried out.Through the simulation and test results analysis,it isshown that compared with the conventional differential protection,the speed of the optical differential protection is faster and the sensitivity is higher and the action is correcter,thus the accuracy of the optical differential protection criterion and the superiority of the protection principle are verified.