Probability Based Worn Circuit Breaker Modeling and Risk Evaluation on Potential Power Grid Failures

Circuit breakers are one of the most commonly applied power protective devices, which are designed to automatically isolate the circuit when the current exceeds a certain limit, to prevent the electric appliances from thermal damage. Circuit breakers can be manually or automatically reset after being tripped. With time elapsing, some mechanisms inside the circuit breakers may get aged and fatigued, and some connections and contacts may become loose and misaligned. The worn conditions may cause the circuit breaker failed to operate, or not able to trip within specified current and time range. These failures and malfunctions may cause discoordination in original power protection plan, and therefore cause unexpected partially or entirely blackout in the power grid. Some cyber attackers may even utilize this flaw to hack power appliances and breach the predefined power protective protocol. Due to the considerable number of circuit breakers in a power grid, simulation approach in system-level power quality, safety and security study is highly demanded. In this work, we propose a probability based simulation modeling methodology for worn circuit breakers. The proposed circuit breaker model will be applied in a micro power grid testbed for risk assessment on potential power grid failures.