Research On Fault Line Selection And Protection Principles Of Four-parallel Transmission Lines On Same Tower

Since four-parallel transmission lines on the same tower (FPTL) have the superiority ofeconomizing land resources, increasing transmission capacity and so on, it becomes aninevitable trend for grid construction in China. However, due to the complicate faults and themutual impedance between FPTL, fault analysis, fault lines selection and Protectionconfiguration are all faced with technical difficulty. This dissertation researches on fault linesselection method, ground-fault distance protection scheme and Current differential protectionfor FPTL. The main contents are shown as following:1. The existing frequency-domain Phase-mode transformation method of FPTL areSummarized. And the characteristics of each sequence component network are analyzed inthis paper, which is the basis for Fault lines selection and protection study of FPTL. Thetime-domain phase-mode transformation method for quadruple-circuit transmission line onthe same tower is studied and two different decoupling matrixes are deduced.2. A new loop flow component fault line selection scheme for FPTL is proposed, whichis based on the characteristics of phase difference between loop flow components andcirculating current component. Due to the circulation components are unrelated with systemimpendence, the proposed method improves accuracy for fault lines selection. The linesselection idea is also extended to more generally applicable asymmetric parameter model. Onthe basis of the feature of phase angles between circulation components, a new approach foridentification the faulty line is also presented. The simulation model of the FPTL isconstructed for the simulation verification based on PSCAD/EMTDC.3. FPTL is usually linked with all kinds of lines to consist of teed line system in complexpower systems. The characteristics of teed structure consisting of FPTL and double-circuittransmission lines on the same tower are analyzed. The mutual electromagnetic effectbetween FPTL is decoupled to obtain the relationship between the inverted-sequence currentof two power source sides. According to that, the fault side is determined and the fault areacan be determined quickly. Positive-sequence voltage difference between non-fault line andfault line is compared. Then the specific fault branch is identified. The simulation resultsshow that the method has high precision and it is independent of fault type, fault resistanceand so on.4. It is not feasible to using traditional ground distance protection in the FPTL single-phase ground fault. In this paper, the relation between the voltage and current ispresented based on the twelve-sequence component method. Furthermore, the compensationcoefficients based on twelve-sequence components are applied to the traditional ground-faultdistance protection. Simulations results show it have high performance.5. Distribute capacitance current on transmission line will decrease sensitivity andreliability of current differential protection. By establishing the Π mode circuit for thetwelve-sequence networks. This paper presents a novel time-domain capacitive currentcompensating algorithm and phasor capacitive current compensation method. Simulationresults verify the time-domain capacitive current compensating algorithm is satified.