Motor contribution to three phase fault currents in a power intensive industry with CPP: A case study

Addition of motor-contribution to the total fault current during a three-phase fault is of interest to all power intensive industries with dominant motor loads. Such results are analyzed for a petrochemical industry where majority of loads are induction motors. Three phase fault currents are computed at five buses of 6.6 kV and also at the main distribution bus of 33 kV. In this case study, the fault currents at 6.6 kV buses are estimated due to the contributions from (i) captive generating units alone (ii) motor(s) connected to the faulty bus only (to that of generating units) (iii) all the major motors in the network including those connected to faulty bus (to that of generating units). The results indicate that for this industry, with captive generation, the motor-contribution to fault currents can be as high as 40%. The transformer rating (and its impedance) feeding the motors play an important role in the motor-contributions to fault currents.