ANALYSIS OF A PASSIVE SUPERCONDUCTING FAULT CURRENT LIMITER

An analysis was carried out to predict the forced response of the equi valent circuit of an innovative superconducting fault current limiter (FCL), The FCE employs two superconducting coils with differing critic al currents wound noninductively. The analysis shows that to reduce th e voltage drop under normal operating conditions, the coupling coeffic ient should be kept fairly high (k > 0.90), For a given coil configura tion (omega L = constant), the limiting capability of the device incre ases with the resistance R of the trigger coil up to a certain value o f R, then further increase in R changes very little the limiting capab ility of the FCL. However, further increase in R can reduce the heat g eneration rate in the device which will help alleviate the problem of relatively long recovery time. The fault current predicted from estima ted values of R compares fairly well with results of an experiment rep orted in the Literature, The discrepancy between the predicted and mea sured current is due mainly to the uncertainty In the estimated resist ance R, because both the purity of Cn and the percentage of Cu in CuNi are neat known. By varying the ratio of NbTi-Cu-CuNi in the matrix, t he purity of Co, and the percentage of Cn in CuNi various values of R, can be achieved, which should help to alleviate the problem off exces sive Joule heating and recovery time.