Fault current calculation and grounding scattering optimization of 220 kV tunnel cable systems

Grounding faults in tunnel cables have received widespread attention. Establishing a fault model for tunnel cable systems in specific environments and proposing a fault current simulation method with high-speed computation and precise calculation accuracy is crucial for its stable operation. Additionally, optimizing grounding scattering method with better fault current scattering ability and conservation of land resources is of utmost importance. The metal sheath fault current of the tunnel cable is deduced using the double-sided elimination method. Based on the finite element method, three types of grounding scattering methods (i.e., spiral, cage and bearing platform) of working shafts are deduced. The ground surface potential of the working shaft is inferred with reference to human body safety limits. The result shows that the maximum cable sheath fault current reach 136.74 kA when the fault location is set at the beginning of the 1st major section. The cage grounding method effectively reduces the fault current density at the grounding point of the working shaft from 13,401.3A/m2 to 7192.8A/m2. When the number of vertical graphene conductors is increased to 6, the ground surface potential of the working shaft is 917.64 V, which is within the permissible range (955 V) for human body safety.