Study on the Charge Transfer Criterion for the Pole-to-Ground Fault in DC Distribution Networks

Botong Li,Xiang Ren,Bin Li

doi:10.1109/access.2019.2931286

Abstract

After a pole-to-ground fault occurs in the DC distribution network using low current grounding, the fault pole voltage drops while that of the non-fault pole rises, which is harmful to equipment insulation and operational safety. Therefore, it is necessary to accurately identify and locate faults with protection equipment. In order to solve the pole-to-ground fault in DC distribution networks using low current grounding, the characteristics of different fault current loops are studied. The distributed capacitance discharging loop at the fault pole, the distributed capacitance charging loop at the non-fault pole, and the feeding of system grounding loop current into the fault grounding point current are analyzed. On this basis, a protection criterion for distinguishing the internal fault from the external fault by the amount of transferred charges, which can be calculated based on the transient differential current, is proposed in this paper. The simulation results show that the proposed pole-to-ground fault criterion can reliably identify the fault line while being immune to the influence of transitional resistance.

Highlights

DC distribution is a new type of power distribution technology based on the voltage source type modular multilevel converter (MMC) [1]–[3]
By analyzing the transient characteristics of the pole-toground fault in cable lines in the DC distribution network, the line capacitance transferred charges calculated according to the line differential current can represent the difference between the internal fault and the external fault
The protection criterion for the pole-to-ground fault in DC distribution networks based on capacitance transferred charges is proposed

Summary

INTRODUCTION

DC distribution is a new type of power distribution technology based on the voltage source type modular multilevel converter (MMC) [1]–[3]. In [20], the zero-sequence fault network is analyzed under the condition of a medium-voltage DC distribution system with highimpedance grounding or ungrounded neutral points Based on this, it proposes a fault feeder line location method by calculating the line capacitance-to-ground. The charging current flows from the negative line through the MMC stations to the fault ground point at the positive pole. As can be seen from (3), (5) and (7), after the grounding fault reaches the steady state after the transient process, the amount of charges flowing into the fault point is certain, which is only related to the capacitance of the positive and negative cable lines and the line operating voltage.

INTERNAL POLE-TO-GROUND FAULT

FAULT-POLE IDENTIFICATION CRITERION

IDENTIFICATION CRITERION FOR INTERNAL FAULTS AND EXTERNAL FAULTS

CONCLUSION