An optimal overcurrent protection strategy for mitigating the impacts of opportunity charging stations in distribution systems

Abstract

The rise of Battery Electric Buses (BEBs) in urban transportation networks, and the adoption of Opportunity Fast-Charging Systems (OFCSs) to support their operation, demand a close examination of the impact of these technologies on protection systems. Thus, this paper analyzes in detail the effects of OFCSs on conventional overcurrent protection schemes and proposes a novel mitigation strategy to the energization and fault plus load effects introduced by this charging strategy on protection systems. The proposed approach includes additional constraints in the overcurrent coordination problem to minimize operation times and uphold coordination delays between main and remote backup protection. Additionally, the resulting optimization problem is solved with the Water Cycle Algorithm (WCA), and is validated on the IEEE 34 and IEEE 123 test systems. In overload situations, the strategy yields a minimal increase of under 200 ms in main protection response times, ensuring non-activation during BEB connections, whereas in non-overload scenarios, optimal settings maintain comparable response times. The paper concludes by recommending coordinated cut-off mechanisms with grid operators to prevent unmet demands during extended BEB connections, addressing critical challenges in the evolving landscape of BEB charging.

Keywords

• Battery electric bus
• Opportunity fast-charging system
• Overcurrent
• Protection scheme
• Primary protection
• Remote backup protection