Fault Current Limiter (FCL)

1. Brief introduction of the fault current limiter (FCL)

Key technical problems affecting safety and stability of power system
Among all accidents occurring in the power system, short circuit is one of the major faults affecting safe and stable operation of the power system. Endangering various electrical devices like breaker, transformer, mutual inductor, and bus bar, wires of substation, short circuit is the big trouble and key technical difficulty for various power grids, and has become a major bottleneck of the advancement of power construction.

Disadvantages and limitation of the present overcurrent protectors
The breaker, which is the main device providing overcurrent protection, has limited breaking capacity and no current-limiting function. Besides, it is not economical when the breaking current reaches 40kA, and the break time is as long as 60 to 200ms. In this case, two problems arise. Firstly, the breaker is unable to break the short circuit current when the current is beyond its breaking capacity. Secondly, even if the breaker breaks short circuit current, electrical devices can still be damaged as the breaking time is overlong.

High end new type fault current limiter (FCL)
Applying world leading brand new idea, Rongxin takes the lead in developing advanced short current protection technology. Rongxin serial fault current limiters can limit short current within 2ms to a level acceptable to the domestic breakers. Besides, the fault current can be restricted to any lower value according to requirement of users. Therefore, the fault current limiter (FCL) functions to limit short current and protect electrical devices.

The fault current limiter (FCL) is suitable for power systems of different voltages between 400V to 500kV and can be applied in system interconnection, bus section, personal power source connection with public utility grid, and parallel connection with reactors to protect generators and transformers, etc.

2. Technical features
a. Complete fault current limitation (In Fail-Safe Mode)
b. Triple protection to ensure reliable operation
c. No need of altering existent relaying.
d. Single phase working mode
e. Telemonitoring
f. Free of maintenance

3. Featured function
Triple protection and safety of the fault current limiter (FCL)
When there is short circuit fault, voltages at both ends of the capacitor will rise rapidly. In this case, if the thyristor does not act quickly, the capacitor will break down under overvoltage. Therefore, capacitors must be multiply protected to prevent breakdown caused by short circuit and lightening strike. The metal oxide varistor (MOV) will act as primary defense to ensure the allowable voltage of capacitors when the thyristor must close, or the MOV will be hot and blow out by possible loss of trigger pulse or switching failure. At this moment, high speed switch will function as the tertiary defense to prevent risks caused by failure of electronic power switch. With redundancy design, the high speed switch and power electronic device add reliability to the fault current limiter.

4. Performance index
Rated voltage/current: 66kV－500kV/1000A－9000A
Short-circuit current damping (current limiting impedance): Either short-circuit current is controlled at less than 40kA or short-circuit current damping can be adjusted as you need.
Voltage drop of steady state operation : <1%
Response time: 2ms
Recovery time: Approximately zero. Thus the fault current limiter is suitable for power system with high speed reclosure and multiple failures.