Structure of a single phase SICSFCL

Saturated iron-core type superconductive fault current limiter --Products can be designed, manufactured, and delivered per customer specifications with rated voltage up to 220 kV.

Fault current limiter is a device to reduce fault current level when a short-circuit takes place in an electric power network.The reduction of fault current level brings numerous benefits to utilities, such as requiring less capacity circuit breakers, lowering the withstand short-circuit obligation for online equipment, reducing the possibility of equipment damage, etc.These benefits make power grids safer as well as less costly for old grid upgrading and new grid construction.

An SFCL, capable of associating low impedance at normal operation conditions to large impedance at short-circuit conditions, is an ideal short-circuit current limiting device for power grids. This could not have been achieved by the conventional fault current limiters. Therefore, SFCL promises to have high demands from utilities and hence have great market potentials.

The photo picture of the laboratory test model.

The major components of a saturated iron-core type SFCL include iron-core, ac coils, and the dc superconductive coil, which is contained in a cryostat.A magnetization control circuit allows the iron-core to be saturated or de-saturated depending upon the functional requirements.An energy release and voltage-surge protection unit can promptly discharge the magnetic energy accumulated in the iron-core and suppress the induced and surge voltages of the dc circuit in a current limiting event.SFCL features sufficiently low impedance throughout normal power transmission, sufficiently large impedance under fault conditions, rapid detection and initiation of limiting action, and fast recovery to normal operation after the clearing of a fault. The power supply provides the dc coil with a constant current for magnetizing the iron core.When a short-circuit fault is detected, the circuit control will send a signal to the high speed switch and the dc circuit is switched to open.We used High Voltage Insulated Gate Bipolar Transistors (HVIGBT) for the high speed switch.The magnetic energy stored in the iron core is then released through the energy release unit.Piezoresistors in the energy release unit also suppress the voltage surge caused by the quick opening of the magnetizing circuit, protecting the elements of the circuit.The total time from the fault detection to the completion of the required magnetic energy release is less than 5 milliseconds.That is to say what the device enters into a high impedance state for current limiting in 5 milliseconds.

In practice, making the dc bias coil with superconductor can: (1) reduce the size and weight of the device, (2) eliminate the joule heat and the associated problems of heat removal, and (3) lower equipment operational loss.Thus, it is the high temperature superconductor that makes the controllable magnetic core reactor type fault current limiter practically feasible.

Through independent R&D and innovation, we have successfully developed the saturated iron-core SFCL technology. In 2007, we designed and manufactured a 35kV/90MVA prototype and installed it in a transmission network at 220kV Puji substation of China Southern Power Grid for live-grid operation, making Innopower a leading player in SFCL area.

Key operating parameters of the 35kV/90MVA prototype ASICSFCL

An SFCL may be used:

1. To solve the problems of extremely high short-circuit current levels brought by integration of power transmission and distribution networks, making high-voltage and super high-voltage interconnections more reliable;

2.To protect larger transformers against short-circuits, and thereby prevent the equipment damage and costly outages;

3. To build a ¡°firewall¡± between the generator and the power grid to isolate the impact of a short-circuit.

To combine SFCL with the existing protection system may form a ¡°relay protection-circuit breaker-SFCL¡± mode, which can provide a more reliable protection system and further strengthen power grid¡¯s integrity.