Abstract
The inclusion of distributed energy resources (DER) in Microgrids (MGs) comes at the expense of increased changes in current direction and magnitude. In the autonomous mode of MG operation, the penetration of synchronous distributed generators (DGs) induces lower short circuit current than when the MG operates in the grid-connected mode. Such behavior impacts the overcurrent relays and makes the protection coordination difficult. This paper introduces a novel adaptive protection system that includes two phases to handle the influence of fault current variations and enable the MG to sustain its operation. The first phase optimizes the power flow by minimizing the generators’ active power loss while considering tolerable disturbances. For intolerable cases, the second phase opts to contain the effect of disturbance within a specific area, whose boundary is determined through correlation between primary/backup relay pairs. A directional overcurrent relay (DOCR) coordination optimization is formulated as a nonlinear program for minimizing the operating time of the relays within the contained area. Validation is carried out through the simulation of the IEEE 9, IEEE 14, and IEEE 15 bus systems as an autonomous MG. The simulation results demonstrate the effectiveness of our proposed protection system and its superiority to a competing approach in the literature.
Highlights
The rising demand for uninterrupted power supply and the rapid growth of infrastructure have motivated the introduction of MGs
We provide a detailed example to illustrate the application of our protection system on a variant of the IEEE 9 bus
We considered dynamic loads, where the active and reactive power loads have increased by different amounts through each load bus simultaneously
Summary
The second phase tackles unbearable disturbances, such as line failures that cause fault current variations In this phase, we introduce a novel strategy to contain the failure within a specific zone and identify the impacted relays. Overcurrent Protection Overcurrent protection is commonly used for conventional distribution systems due to its low cost and ease of deployment This type of protection requires some modifications so that it can be utilized for mesh-connected MG with DERs. In an autonomous mode of MG operation, the fault current level is reduced, and long tripping time is required to detect faults [17]. The adaptive protection system of [23] solves the coordination problem by minimizing the operating time of all primary relays in the MG They did not consider the small disturbances that the MG is susceptible to. The MG is often equipped with a set of protective devices, relays and circuit breakers, to mitigate the risk of unexpected dynamic events
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