Research On The Pilot Protection And The Fault Phase Selection For Double Circuit Lines On The Same Tower

The double circuit lines on the same tower have been widely used in our state grid as it may increase the transmission capacity of each way, reduce used ground and save cost. Because of the large number of circuits, the small distance between the double circuit lines and special fault types, there are many different Changes in electrical characteristics and mutual inductance from the normal circuit lines or double circuit lines operated in parallel, the protection used for double circuit lines is insufficiency in characteristic. The protective relay may have incorrect action in the double circuit lines. because the double circuits increase the transmission capacity, so the multiphase autoreclosure must work correctly during the cross country faults in double circuit lines in order to avoid unselected trip and enhance the reliability of power supply. So the research on the double circuit lines on the same tower protective relay is very important for improving the relay performance and the steady of the grid.There are many aspects of the study in the double circuit lines on the same tower protective relay. Because there are many problems in the fault phase selection, pilot distance protection and directional comparison pilot protection. This paper will mainly focus on the above-mentioned research work issues.First of all, the paper analyze the research and application of the protective relay on double circuits, Focusing on the fault phase selection, pilot distance protection and directional comparison pilot protection problems, then Describes the highlights and main features of the paper.Because it is difficult to analyze the changes in electrical characteristics and the action of the protective relay, so it is very important to build a simulation platform. The simulation based on the sequence components can not simulating the actual situation of the double circuits lines on the same tower, so the research build a simulation platform based on the structural parameters to simulate the changes in electrical characteristics and the influence of transmission parameters, including the design of transmission wire parameters ,tower model ,and the algorithm based on frequency dependent (Phase) model. The research also design the Data output interface and Fault location in order to analyze the changes in electrical characteristics and the action of the protective relay. The fault phase selection is a key factor whether the fault line may be cut off according to selected phase by pilot protection. The fault phase selection only can use all voltages and currents of one circuit. The research shows that the phase current difference suddenly-change and the sequence current elements can not trip correctly under various cross country faults in double circuit lines. The paper analyze some typical fault phase selection and then propose a new fault phase selection theory. The theory first use phase voltage suddenly-change and phase voltage stable state quantity to make sure the fault types. the use The phase and amplitude of fault phase current and directional impedance relay to judge the real fault phase. The simulation results show the effectiveness of the proposed phase selection theory.The distance relay may appear a large error during the cross country faults in double circuit lines. At the same time the zero-sequence mutual inductance between two circuits will also impact the grounding distance protection.the paper. The paper use the phase of zero-sequence current of two circuits to analyze the impact of the zero-sequence mutual inductance between two circuits. According to the non-ground cross country faults, the paper analyzer the error of the phase to phase impedance and the solution.The negative-sequence directional and zero-sequence directional can guarantee the correct action during simple fault, but the cross country faults belong to complex fault, so it is necessary to analyze the action situation of the directional relay. The paper use six-sequence component and current phasor diagram to analyze the problem of the directional relay during the cross country faults. The simulation results show the The effectiveness of the proposed phase selection theory.