New Differential Protection Theory Research And Its Application In Wide-Area Protection

With the rapid developments of Chinese economy, the demands of electricity isgrowing which leads to the gradually expansion of power system capacity and thecomplication of power grid construction. The intricate running status have given rise tothe complication and diversification of the potential safety hazard. To eliminate the safetyhazards, the standard of relay protection must be more restricted. Meanwhile, thefrequently occurrence of mal-operation and the accidents of power cut in several areashave indicated the traditional protection system can not guarantee the safe running of thewhole power system. How to make the running power system safer and more stable,scholars have made massive studies in two sides as follows: firstly, expand traditionalmain protection theory and fulfill its intellectualization and self-regulation; Secondly，replace traditional backup protection with wide area backup protection using wide areamultipoint information.This thesis will also study from these two sides.It has been the focus of study to improve the security and sensitivity of transformerdifferential protection recently. Because of the higher sensitivity, differential protectionbased on fault component has been wildly used in practice. But it is impossible fortraditional criterion of differential protection to improve both the security and sensitivityof protection by means of setting fixed characteristic curve. A new criterion for adaptiveprotection that can adjust the parameters of protection characteristic according to runningstate of power grid is proposed. Compared to traditional fault component baseddifferential protection, this new protection criterion has higher sensitivity and security,which can distinguish internal fault from external fault reliably. The main protectionmal-operation accident under the circumstance of core over excitation is also analyzed,and an improved setting calculation method that can adjust the threshold currentaccording to flux density of the transformer core is proposed to solve this problem. Thefeasibility and superiority of this method is proved by lots of dynamic simulation tests onUHV transformer. The ability of the new criterion to avoid mal-operation under thecircumstances of TA partial transient saturation is also analyzed.The basic function of wide area protection system and the necessity of divideassociated area for protection IED is analyzed. This thesis also put forward a fewcommon wide area protection structure，and made a comparison between them. Besides, the working mode of wide area relay protection system is discussed and then theprinciple to divide protection IED associated area based on Petri net theory is proposed.Double-bus and double-circuit connection and one and a half circuit breaker connectionare taken as the examples to study network topology to meet the requirement ofprotection associated area division.In the last part, this thesis chose differential protection criterion as the operationcriterion of wide area protection after comparisons between the two common operationcriterion. Then the wide area protection algorithm based on the tuples is proposed, andthe feasibility and superiority of this criterion is proved by analyzing the IEEE5nodalpoints system and by making comparisons between this algorithm and the algorithmbased on graph theory.