Fault Characterisation of a DC Microgrid with Multiple Earthing under Grid Connected and Islanded Operations

Abstract

Direct Current (DC) microgrids are gaining an international interest to improve the flexibility and the reliability of future distribution systems. DC microgrids are more suitable and efficient infrastructure for connecting and controlling distributed energy resources. However, they do present new challenges under different fault conditions. To design appropriate protection solutions to handle such challenges and ensure DC microgrid secure operation under different operation modes (grid-connected and islanded), there is a need to fully understand their fault behaviour under each DC microgrid mode. Therefore, this paper investigates in detail the fault behaviours associated with DC microgrids with local distributed energy resources under different fault conditions (e.g. DC pole to ground and pole to pole faults). A DC microgrid modelled in PSCAD/EMTDC with the appropriate layout, multiple earthing and control structures is used as a test network in the simulation fault studies.

Fault Location in DC Microgrids Based on a Multiple Capacitive Earthing Scheme

“…A pole-to-earth is applied at different locations whereas the pole-to-pole events are not considered in this study. Ref [16] studies the latter cases and as the capacitors provide an instantaneous path to ground, they exhibit a similar response to pole-to-earth faults (i.e. Vdc to true earth).…”

“…A multiple capacitive earthing scheme has been proposed for DC microgrids in order to prevent DC current leakage in the protective earthing conductor (under normal operating conditions) and also to form a conducting fault path during DC pole-to-earth faults [15], [16]. In a practical sense, such a scheme helps to minimize corrosion at adjoining infrastructure.…”

“…Active methods are based on signal injection (usually by deploying auxiliary equipment) to the faulted feeder, followed by the analysis of the reflected signatures. Passive fault location methods are solely based A. Makkieh, V. Psaras, R. Peña-Alzola, D. Tzelepis and G. Burt are with the Institute for Energy and Environment of the Department of Electronic and Electrical Engineering at the University of Strathclyde, 16 Richmond St, Glasgow G1 1XQ. Scotland, United Kingdom.…”

Capacitive earthing charge-based method for locating faults within a DC microgrid

“…In this circuit it is assumed that the capacitor Ce is initially discharged. The resistor, Rf, represents the fault resistance and the charging behaviour of the capacitor is described in (2) and 3 Indeed, charging the capacitor will cause a voltage swing in the whole network and therefore it is necessary to clamp the voltage across the capacitor to prevent a complete charging of the capacitor. This can be done with the help of a voltage clamp which will be described in the following subsection.…”

“…INTRODUCTION Direct current (DC) microgrids are expected to play an important role in facilitating the connection and control of distributed energy resources (DERs) to meet future low carbon energy policy [1]. Generally speaking, DC microgrids performance under normal and faulted conditions are highly influenced by their interface to the AC grid and by their operation state grid-connected or islanded [2]. One of the remaining challenges is the requirement for accurately locating DC faults.…”