Research On Fault Current Limiter Based On Vacuum Arc Current Commutation At Power Frequency Zero

With the increase of the power grid capacity, the fault current is becoming bigger and bigger. In some regions of China, the limitation of the interrupting capability of the circuit breakers has made an important effect on the further development of the power grids.For solving the interruption problem, a fault current limiting scheme is proposed which works on vacuum arc current commutation at power frequency zero and ignores the first half cycle of the fault current. It is realized by a fast vacuum switch and a current-limiting-impedance connected in parallel. The fast switch is normally closed for passing the normal current and opens quickly when having a fault, the fault current transfers from the fast switch to the current limiting impedance at the first power frequency current zero, and is therefore limited. The circuit breakers which should make response to the fault normally make interruption of the fault current after the first power frequency zero and then the current has been limited.Computation and tests were performed to investigate the current commutation. The computation was carried out by using PSCAD software to watch into the fault current commutation from a fast switch to an inductor. It showed that inductors can be used as the current limiting impedance without producing serious overvoltage. Tests were carried out with an oscillation circuit facility in which a power frequency current up to 80kA can be produced to simulate a fault current. In the test, a current of 36.8kA(peak) was successfully commutated from a vacuum switch(rated fault current interrupting capacity of 30kA) to a current-limiting-inductor of 3.3mH.Discussions were made on the issues related to the feasibility of the fault current limiting scheme, which including the influence of the unlimited first half cycle of the fault current on the power grid and the power equipment, the current computation ability of the fast switch.