Analysis and solutions of overcurrent protection issues in a microgrid

Implementation of microgrid concept creates several issues to the existing protection scheme in the radial distribution network. Contribution of short-circuit current from the main grid and distributed generations result in variations of fault current levels inside the microgrid depending on the location and capacity of the distributed generators. The changes cause detrimental effect of sympathetic tripping, blinding of protection, relay over-reaching, relay under-reaching and loss of selectivity of the overcurrent protection scheme. Such issues must be managed carefully to ensure full benefit from microgrid adaptation. Analysis of the existing overcurrent protection schemes applied in a microgrid with distributed generations reveal the incapability of the system to adapt to the new challenges. Some solutions that could rationalize the protection challenges are also presented in this paper.