A fault current limiter (FCL) is a device which limits the prospective fault current when a fault occurs (e.g. in a power transmission network) without adding impedance to the circuit during normal operation and therefore protecting the grid. Simplified: it transmits current during normal (superconducting) state, without any resistance.
If a fault current occurs, the system exceeds its capability, changing into a non-superconducting state with very high resistance, thereby limiting the current and protecting the next grid. Once the fault current is gone, the system will fall back into its superconducting state.
The superconducting coils typically are submerged into a cryogenic bath, usually liquid nitrogen. These baths will have a continues loss of LN2 due to heat inleak through insulation and cable connections. To compensate for these heat losses, Stirling Cryogenics has designed cooling concepts that can be built in different sizes to provide the required cooling power for the size of FCL to be built.
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