Research On The Adaptive Single-phased Current Differential Protection For Power HV Transmission Line

The power grid that is going to more and more complex and multiple day to day, and the rapid development of power system, will make the single-phase current differential protection be the main protection for power HV/EHV transmission line. However, the digital single-phased current differential protection device existing in currently has some defects on criterions and communications, this make its performance unsatisfied. Aiming at the direction, the research of this paper is to design a new single-phased current differential protection with the better performance and more meeting to the needs of power development at present, using the newest digital protection technology and communication technology. Criterion is a perpetual topic of relay protection. After analyzing the advantages and disadvantages of the domestic and alien current differential protection criterions, an adaptive single-phased current differential protection criterion is put forward. The new criterion is the fault component with variable vector windows fitting in high-low threshold inverse time leg tipping in 50 ms fault time, and the whole current differential protection, the fault component protection, zero-sequence and negative-sequence current protection after 50ms fault time. The feasible solutions to capacitance current, TA saturation, TA wire break, weak feed system, are presented. While, the way using directional element not identifying TA saturation, to TA saturation problem is an innovation in this paper. Synchronic adjustment of each terminal data is a key to making current differential protection into reality. Basing on analyzing the ways of Synchronic adjustment, an improved means using data amendment based on the number of sample. The theory of this means is very simple, and it can meet to the requirement of sync not add to any hardware component. Additional, the present mode of communication between the current differential protection devices is lack of adaptability. To overcome this shortcoming, the adaptive communication mode which combines the special optical fiber channel and compound PCM is designed. That is to supervise the commutation channel, recognize the working condition and realize the switchover between them, improve the reliability of channel greatly. At last, the results of ATP emulation and static simulating trial indicate: the adaptive single-phased current differential protection researched in the paper is a more desired protection for transmission line. It can change its operating criterions, communication mode to optimize the performance of protection on real time, according to the running condition of power system and communication equipments, and the alteration of fault status.