Research On Fault Line Selection Analysis Method For Multi-circuit Lines On The Same Tower

Both domestic and foreign researches or practices of multi-circuit transmission technology on the same tower show that the use of multi-circuit transmission lines on the same tower is an effective method to well deal with the tension in the transmission corridor,saving land resources,increasing transmission capacity,and better achieving coordinated development of not only power grid construction but also local development.So this essay focuses on the analysis of fault selection criteria for symmetrical double-circuit transmission lines on the same tower,asymmetrical double-circuit transmission lines on the same tower,symmetrical four-circuit transmission lines on the same tower,and special T-type transmission lines.After these analysis we can get the following results and conclusion:Based on the symmetrical component transformations,according to the characteristics of the line and the operating mode,a double-circuit transformation matrix suitable for uniform distribution is derived after two diagonalization calculations.This matrix is a matrix of the time-domain algorithm,which costs less calculation than symmetrical component transformations.Using the modulus relationship between the transformation matrix and the current component,new parameters named W₁ and W₂ are defined,according to the different of the two parameters between various faults,a new fault line selection criterion was then proposed.Thus the two asymmetric parametersf₁ andf₂ were introduced,and through further mathematical calculations,the double loop transformation matrix suitable for the asymmetry parameter was then derived.After the transforming of matrix and current components,it is found that the introduced asymmetry parameters will not affect the criterion of the line selection.And what need our attention is that this method is also applicable for four-circuit lines.The six-order impedance matrix is increased to twelve-order on the base of two-circuit line with symmetrical parameters.Using the same principal ideas,a phase-mode transformation matrix suitable for four-circuit lines could also be derived.Twelve modes can be extracted from the current component,and a new fault line selection criterion is proposed after four new defined parameters,W1’,W2’,W3’and W4’.Experimental simulations are carried out under the different distances,transition resistances and fault types conditions.The results show that the proposed criterion is efficient,simple and accurate.As for the actual applications of transmission lines,T-type transmission lines can flexibly change the connection mode,reasonably allocate power resources and improve the utilization rate of electricity according to users’required power demand.To conclude,through this paper,the line selection of a special T-type transmission line composed by a four circuit line and two single circuit lines is analyzed.The reverse sequence current extracted from the four circuit line is used to analyze whether there is any fault on the four circuit line,if so,the voltage-difference method can be used to determine which circuit it occurs in,otherwise,in order to judge the fault of the other two single circuit lines,the current vector differential method will be carried out.Lastly,PSCAD/EMTDC experimental simulation shows that the proposed transformation matrix and fault line selection scheme which was mentioned in this paper are effective,reliable and not sophisticated.What’s more,it also shows that the method would not be effected by fault distance,transition resistance and fault type.