Development and Field Trial of a Hybrid Fault Current Limiting Circuit Breaker

The increase and penetration of renewable energy production in the electrical distribution network may lead to increased fault levels in existing systems. In combination with the trends of electrification of vehicles and domestic heating, there is an increasing need for reinforcement of the medium voltage electric distribution network. This paper presents a fault current limiting circuit breaker (FLCB) that limits and interrupts a fault current in a 12 kV system within 1 millisecond after detection. The device is based on a hybrid topology, where fast mechanical switches are combined with power semiconductors to perform the switching operations. In the event of a 25 kA prospective short-circuit current, the peak current is limited to 13 kA and thereafter decreases to zero within a few milliseconds. After the interruption, the device can be reclosed within minutes to reenergize the system. In a collaboration project between ABB and UK Power Networks, a device was developed and tested. The functionality of the device was proven in a two year long trial in the electric distribution network of London. During the trial, several real network faults were limited and interrupted. Limiting and interrupting a fault current before the first peak gives new opportunities in the design and connection of the system. As the duration of the fault current through the FLCB is so short, it does not affect the system circuit breakers. Hence, the FLCB can be used to allow more generation in a system without a need to upgrade the system substations and switchgear. Another possibility is to use the FLCB as a bus coupler, to interconnect different parts of the system, decreasing the losses and increasing the redundancy in the system. In the event of a fault, the FLCB quickly sectionalizes the system, and allows the system protection to handle the fault.