A novel protection scheme for an LVDC distribution network with reduced fault levels

Abstract

Low Voltage Direct Current (LVDC) distribution is one of the new promising technologies that have the potential to accelerate the wider integration of distributed renewables. However, adding new power electronics to convert AC to DC will introduce new forms of faults with different characteristics. Converters with inherent fault current limiting and blocking capabilities will significantly limit the fault currents, resulting in significant impacts on the performance of existing LV overcurrent protection schemes. New protection methods based on the change in the DC voltages have been proposed recently by different researches. The issue with these methods is that the protection relays of the un-faulted feeders will also see the same change in the voltage for certain faults, leading to substandard selectivity and unnecessary tripping. This paper investigates these challenges, and presents a novel DC protection method which is based on the use of the combination of two components: the voltage change (dv/dt) and the change of current (di/dt). The new method is mainly developed to detect and locate DC faults with reduced fault current levels within DC distribution networks. The introduced protection concept is tested on an LVDC distribution network example using PSCAD/EMTDC simulation tool.

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

“…Comparatively, modular multilevel converters (MMCs) which have the potential to be used for future DC microgrid systems have more power fault management capabilities and resilient operation [8]. The half bridge MMC can only limit the fault current transient, whereas, the full bridge MMC can block the DC fault current completely [9]. Regarding to the DC-DC buck-boost converters, the half bridge DC-DC converters lack fault current management capabilities.…”

“…The last stage when the grid side current contribution feeding to the fault location. More details of mathematical expression related to these stages and behaviours can be found in [9][10].…”

Investigation of different system earthing schemes for protection of low‐voltage DC microgrids

“…DC microgrids require fewer conversion stages to host distributed energy resources in comparison to AC systems. The voltage regulation and power balancing are more controllable in DC systems [1, 2]. DC microgrids have already been introduced for several applications such as data centres, information communication systems and electric ships.…”

An Investigation into the Limitations of the Combined dv/dt and di/dt Protection Technique for Compact d.c. Distribution Systems

“…However, limiting fault currents may reduce the effectiveness of widely used protection methods such as overcurrent protection. A technique combining the rate of change of voltage (dv/dt), and rate of change of current (di/dt) has been proposed which has shown promising results for scenarios with reduced fault currents [1]. The method has a potential to be used on shipboard protection system, however, the breadth of fault scenarios must be increased to identify its applicability.…”

“…The combined dv/dt and di/dt has been investigated in radial network configuration and has shown promising results for fast and selective operation for LVDC in utility applications [1]. The scheme detects and locates a fault based on the magnitudes of dv/dt and the signs of di/dt.…”