Research On The New Line Differential Protection Based On Optical Current Transformer

Protection is the safety barrier of the power system, current differential protection as main protection of transmission lines, the protection performance is related to the safe operation of power grid. The traditional current differential protection have two concerns: the shortage-problem of reliability caused by the the transient characteristics of electromagnetic current transformer and low-speed action performance caused by the amount of power frequency protection. As a result of the limitation of principle, the developed method is very difficult to solve the problem at all. According to the above problems, optical current transformer is presented in this paper, and study a new type of full waveform, instantaneous value differential protection scheme, the main research contents include:First of all, aimed at the shortage-problem of reliability, this paper analyses the main reason is caused by electromagnetic current transformer measurement performance defects, the use of optical current transformer to replace traditional electromagnetic transformer, study of the reliability. The results show that:electromagnetic current transformer with iron core saturation problem, easy cause protection misoperation when there is a failure out of the area, reduces the reliability;optical current transformer has no magnetic saturation problem, and able to measure non-periodic dc component, and laid a solid foundation for enhanced reliability.Then, aimed at the low-speed action performance, this paper analyses the main reason is caused by by the amount of power frequency protection. This topic make use of the fault current waveform information, based on the current and the instantaneous value, and puts forward a kind of “energy method” differential protection algorithm. Make “Outside-fault is not maloperation and reduce the action time” as a principle, through the way of setting calculation and checking, through the way of setting calculation and checking, determine the braking coefficient ‘K’and the integral time as window delta ‘t’. The results show that: using the new protection algorithm, may be started after the failure of four week period protection,the action-time can be effectively improved.Finally, in order to further improve the sensitivity of light load line when there have a fault, this paper put forward a “floats momentum” protection algorithm.Making use of “energy method” protection criterion and “floats momentum”protection criterion, this paper proposed a protection plan. The simulation results show that: when the failure occurred out of the area, the full waveform differential protection has good selectivity, not maloperation; when the failure occurred in the area, the full waveform differential protection has good sensitivity and quick action.These results prove the correctness and reliability of the full waveform protection algorithm.The full waveform differential protection has good sensitivity and quick action,providing a new solution for the transmission line protection. This topic research has a positive role to improve the safety level of power grid.