A fault current limiter (FCL) is an electrical device used to reduce the amplitude of the fault/short-circuit current to an acceptable level, especially for the circuit breaker that must clear the fault. Optimally, in normal operation, the FCL ought to be ‘invisible’ to the electrical system, having very low impedance or being bypassed. In case of a fault, the bypass is opened within a few milliseconds and significant impedance or resistance is made ‘visible’ to the system, causing a reduction of the fault current, as shown in the figure below. After the fault current has been cleared, they typically return to normal operation.

FCLs can be simple devices (e.g. an air-insulated reactor) with some disadvantages, like thermal losses. More complex devices using high-temperature superconducting (HTS), resonant circuits or power electronics are also applicable. FCLs are applied in substations either in a feeder with the most significant short-circuit current contribution or in the busbar coupling bay.

There are three main benefits of using FCLs:

• FCLs deliver cost savings by allowing the use of electrical equipment with a lower short-circuit current level.
• FCLs are an effective solution for substations where increases in short-circuit currents are expected due to further meshing of distribution and transmission grids. They can prevent the need for additional busbars or substations and the creation of new network operational groups.
• In distribution networks, FCLs can be used to couple network groups, thereby reducing the number of network coupling transformers, which can also significantly reduce costs.

FCL enablers are listed below:

• The key advantage of applying FCLs in the electrical grid is saving costs and substation space. Therefore, a thorough cost–benefit analysis is typically performed prior to implementation.
• FCLs are unique devices with limited market availability.
• FCLs can have large dimensions, which can make their application in existing substations challenging.

To increase the benefits, feasibility and functionality of FCLs, the following list outlines key areas for future research and development:

• Investigating the forecast of fault current amplitude development in future transmission grids may be a useful R&D activity. This is especially relevant for networks that are becoming increasingly extended into meshed grids and incorporating more power electronic devices (as High Voltage Direct Current (HVDC) converters), which could lead to higher fault currents.
• In distribution networks, FCLs are unique devices, but there is sufficient experience with their application. However, even for simple solutions, further adaptations to specific network parameters or dimensions often require additional efforts and research.
• Cost–benefit and life cycle analyses for sustainability assessments require specific parameters and knowledge about FCLs.
• FCLs have not yet been applied in extra high voltage grids (>245 kV) due to either significant technology disadvantages (such as thermal losses) or the low technology readiness level of HTS current limiters.
• Currently, HTS FCLs are the most promising technology for extra high voltage grids due to the high amount of energy that must be dissipated and the high thermal losses required. Piloting and further research are needed.

The technology is in line with milestone “Demonstration of innovative technologies for power flow control and increasing grid efficiency” under Mission 1 of the ENTSO-E RDI Roadmap 2024-2034.

Examples

TRL 9 for high voltage (≤ 145 kV) reactors.
TRL 3-7 for high voltage (≤ 145 kV) superconducting FCL.
TRL 3-4 for extra high voltage (≥ 245) superconducting FCL.

1. M. Chewale, V. Savakhande, R. Jadhav, R. Kupwade and P. Siddha. (2019). “A comprehensive review on fault current limiter for power network” in Int. Conf. Recent Advances in Energy-Efficient Computing and Communication,

2. Gridon, “Commercial readiness of GridON Fault Current Limiters proven through 33 months in service”, February 2016, GridON.com