Research On Fault Phase Selection For Multi-circuit Lines On The Same Tower

To save transmission corridor channels,reduce the construction cost of power system,improve the transmission capacity and land utilization,the same tower multi-loop transmission line has become the first choice of high voltage transmission in our country,and the safe and stable operation of the line has a significant impact on the national economy.However,there is electromagnetic mutual inductance influence because of the close distance of multi-loop transmission lines on the same tower,which makes the decoupling step more difficult,and makes the relay protection work such as fault analysis and fault judgment difficult to carry out.Therefore,this paper mainly focuses on the same tower double circuit transmission lines,the same tower four circuit transmission lines with symmetrical parameters and asymmetric parameters for fault phase selection analysis.The main contents are as follows:（1）Referring to the decoupling idea of the traditional double loop using the six sequence component method,the phase mode transformation method derived from the new transformation matrix is used to decouple the double loop.The phase current is transformed into sequence current components by using the comprehensive decoupling matrix,and the characteristics of sequence current components under different fault conditions are obtained by combining fault analysis and fault boundary conditions.The new parameter H is set,and the fault line selection and three-phase fault judgment are completed by the value conditions of H and part of sequence current components.Then,through the range of sequence current component I₁ and the positive and negative relationship between defined parameters I_p and I_q,the specific judgment of fault types and fault phases is completed.The simulation results show that the double-cycle phase selection method is not affected by fault type,fault distance and transition resistance.（2）On the basis of the double circuit transmission line,the loop line is expanded into four circuit lines,and the decoupling analysis of the same tower four circuit transmission line whose system impedance matrix is in the form of parameter symmetry is carried out,and the complete decoupling calculation of the phase and mutual inductance between lines is carried out again.Through the inverse transformation of the total decoupling matrix,the relationship between the twelve sequence current components and the phase current components is obtained.Four parameters,W₁,W₂,W₃ and W₄,are defined,and the fault lines are selected by combining the setting values.After determining the fault line,the phase selection process is constituted by using the characteristic relations of the associated current sequence components to select the fault phase.The PSCAD simulation results show the feasibility of the phase selection scheme.（3）The fault phase selection process of the same tower four-circuit transmission line with symmetrical parameters is further extended to the four-circuit transmission line with incompletely symmetrical parameters,and it is necessary to introduce asymmetric parameters to completely diagonalize the impedance matrix and eliminate mutual inductance.The fault line selection,fault type determination and fault phase selection are completed successively by defining parameters in the same principle.The simulation results show that the fault phase can be selected correctly under different fault types,fault distances and transition resistances.