Study On The Wide Area Backup Protection Of The Transmission Line

To 2010,three huge interconnected power girds in north, middle and south of China will come into being. With power grid interconnecting widely, a higher demand to the stability of the power system has been put forward. It is desired that not only faults can be isolated fastly,accurately and dependably, but also system can preserve steady operation while greater disturbances take place. Conventional line backup protection relays based on their locally measured information are component protection. The backup protection relays are accomplished through the cooperation of the action times, action values and action regions. With the increase of the power system capability and the complicated system structure, it troubles the cooperation of the protection value and action time,and the component protection consider little of the impact the whole system.Wide area protection systems have wide view of the power grid based on their wide measured inputs. They can offer more accurate and dependable faults isolation, and at the same time, they considerate the influence on the system operation and prevent disturbances from protection actions.In this thesis, the characteristics, function making up and system structures are discussed. In this dissertation, the background and research situation of the wide area protection are introduced.The principle of transmission lines' directional protection is discussed in this thesis, wide area backup protection based on directional comparison principle of fault components of voltage and current is introduced.Power direction is judged by the directional component based on zero-sequence current and negative-sequence current, then the result of power direction is used by the directional arithmetic and fault position is determined. Theory analysis and simulation experiments show that: the method has high sensitivity while fault happens in the zone of protection. But the reliability is poor. To assure the reliability when power system is nomal or the outer fault is cut off, the amplitude of fault components of voltage and current must be used in the method.The principle of transmission lines' current differential protection and the topological structure of power system are discussed in this thesis, An wide area current differential backup protection based on topological tree is introduced. Protection zones are determined with the help of topological trees, and the calculations of differential current are accomplished in thire protection zones. Theory analysis and simulation experiments show that: the mothed can judge out the fault locates correctly and cut off the fault in minimum zones. The shortage of the mothed is that the numbers of current sample values are huge, with the widen of protection zones, the exchanged information of current is increase,and the request to communication system is higher.