Single-Pole-to-Earth Fault Section Detection of the MVDC Cables Based on Variation Mechanism of Grounding Line Currents

The multiple-conductor structure of the medium-voltage direct current (MVDC) cable results in complex electromagnetic couplings, posing great challenges to analyze variation laws of grounding line currents which can be used to detect the single-pole-to-earth faults (SPTEFs). In this paper, the equivalent circuit models of the MVDC cable in both normal and fault conditions are constructed by considering electromagnetic couplings between multiple conductors of both poles. The variation mechanism of the grounding line current before and after a SPTEF is explained by theoretical analysis. Considering communication methods in practice, two fault section detection criteria are proposed based on variation features of grounding line currents. The experiment model of a MVDC cable system is established by RTDS real time simulators. The method is only validated by hardware in the loop simulation. The simulation results show that the method is applicable to both ordinary faults and high-impedance ones with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3000\Omega $ </tex-math></inline-formula>. The fault detection accuracies can reach 99% with 20dB noises while they are no less than 95% with ±10% measurement errors. The shortest time for implementing the method is only 0.1ms. The comparison work shows the advantages of the method.