Fault Current Limiters

A fault current limiter is a nonlinear circuit element used to protect grids when a fault occurs. It has a low impedance at normal current levels, but presents a higher impedance at fault current levels. The switching between the two states needs to be extremely rapid to both protect other devices, and to ensure an uninterrupted supply.

superconducting_props

This rapid switching is often achieved using a superconductor. This quenches when the fault occurs, and the change from superconducting to resistive state provides the necessary (very rapid) switch.

Opera-3d uses a Finite Element model to simulate the local temperature rise that occurs, and propagates, during a superconducting quench. The superconductor’s critical current density is defined as a function of the local temperature and magnetic flux density. This is used to determine material properties as the superconductor transitions from the superconducting to the resistive state. The electromagnetic and thermal analyses are coupled to a circuit representation of the coil to calculate currents in the windings. Where additional entities need to be included, such as a conducting former or shielding, the quench module will also couple to Opera-3d’s transient electromagnetic solver for a full solution. By coupling the analyses, the non-linear behaviour during the quench process can be modelled and investigated in detail.

twisted cable

Modelling material properties as a function of the local field and temperature is essential for an effective simulation of the quench process. This is because the process is highly non-linear (some material properties varying by orders of magnitude during a quench). In Opera-3d the critical current density of the superconducting material is defined as a function of temperature and magnetic field using functional tables, which allow users full control over the material properties. Opera-3d can simulate systems comprised of complex superconducting cables with high levels of anisotropy and non-linear behaviour. Both low-temperature (LTS) and high-temperature (HTS) superconductors can be modelled. The quench module is supplied with material properties for Sumitomo HTS materials.

For further details on Opera for this application please contact us

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