|
|
|
Short circuits are inevitable events but now there is an effective protection against the occurring high fault currents, the Superconducting Fault Current Limiter (SFCL). Designing grids in order to withstand the increasing short-circuit currents is a big challenge for network providers. With conventional techniques none, or at least no satisfying solution is available on the market.
Destribution network operaters are today challanged to take a huge effort in laying out their grids against steadily increasing short circuit currents. With conventional technology there is no or at least no sufficient solution for an effective short circuit limitation.
Nexans SuperConductors has developed a modular concept for superconducting fault current limiter systems which can be adapted for changing requirements. First devices for medium voltage applications were delivered to customers in Germany and England and have been integrated into the power grid.
|
| |
|
|
Functionality
Solely the characteristics of superconducting materials now open new possibilities: under normal operating conditions the superconductors show only a very small impedance, i.e. from the electrical standpoint they are effectively invisible within the grid. Only in case of a grid failure the SFCLs automatically demonstrate their limiting function. Thus being based on the particular material properties, the SFCLs can be considered as intrinsically safe which for grid operators is one of the primary demands for a device.
SFCL systems handle fault currents completely autonomous and after the fault is cleared, the SFCL system automatically returns to its original state without any electronic or external action. The SFCL system does not interrupt the current completely but limits it to a well defined value. On this account SFCL systems can be adapted into existing protection configurations and network structures very well.
Superconducting fault current limiters can be considered strongly simplyfied as self-regenerating fuses. Supraleitende Strombegrenzer können stark vereinfacht als selbstregenerierende Sicherungen betrachtet werden. Following the principle of resistive fault current limiters the superconducting material is connected in series into the current path. Above a distinct current value the superconductor loses its superconducting properties and creates instantaneously within milliseconds a resistance which limits the current even in the first half wave. Advantages of this principle is the intrinsic safety and the limiting effect withour inerrupting the current.
The resistive SFCL in series connection also minimizes the phase shift of current and voltage during a short circuit event, which limits the stresses and requirements to the circuit breakers because current and voltage have zero crossing nearly at the same time. This means that all breakers, cables etc. which after the SFCL can be layed out for lower stresses and cost for these devices can be significantly reduced.
