No abstract

The integration of high bandwidth energy storage systems (ESS) in compact DC electrical power systems can increase the operational capability and overall flexibility of the network. However, the impact of ESSs on the performance of existing DC protection systems is not well understood. This paper identifies the key characteristics of the ESS that determine the extent of the protection blinding effects on slower acting generator systems on the network. It shows that higher fault impedances beyond that of an evaluated critical level will dampen the response of slower acting generator systems, decreasing the speed of corresponding overcurrent protection operation. The paper demonstrates the limitations of existing protection solutions and identifies more suitable protection approaches to remove/minimize the effects of protection blinding.

DC microgrids have the potential to radically disrupt the distribution system market due to the benefits offered in easing the integration and control of distributed renewable energy resources and energy storage systems. However, the nonzero-crossing fault current profiles associated with short-circuited DC systems present a major challenge for protection. Isolation of faulted networks prior to the peak-current discharge of DC side capacitors may address this challenge if rapid fault detection speeds (shorter than 2ms) can be achieved. Accordingly, novel methods of utilizing the rate-of-change-of-current (di/dt) have been proposed in the literature to realize new, high-speed distance protection strategies. This paper proposes two practical methods for optimizing the numerical computation of di/dt of fault current transients and evaluates the performance of each within a MATLAB/Simulink model of a DC microgrid with artificially injected measurement noise

No abstract

This paper proposes a novel solution to the issue of protection instability caused by time synchronization error in high-speed differential protection schemes for DC microgrids. DC microgrids provide a more efficient platform to integrate fast-growing renewable energy sources, energy storage systems, and electronic loads. However, the integration of distributed generators (DG) may result in variable fault current magnitude and direction during fault conditions, potentially causing mis-coordination of conventional time graded overcurrent relays. One identified solution to this issue utilizes high-speed differential protection schemes to maintain effective selectivity in DG-dominated DC microgrids. However, as DC short-circuit fault currents are highly transient, microseconds of synchronization error in the measured line currents may cause protection stability issues, whereby mal-operation of relays may occur as a result of faults external to the protected zone. This paper investigates the impact of time synchronization errors for high-speed differential protection in DC distribution systems. It then proposes a multi-sample differential (MSD) scheme that performs multiple differential comparisons over a sampling window to ensure the stability of high-speed differential protection schemes for external faults whilst maintaining sensitivity to internal faults.