A voltage sag study in a large industrial distribution system

The method of fault positions has been used to study the post-fault voltage sags in the supply to a large chemical industry plant. The main concern is faults in the on-site distribution systems. The during-fault and post-fault voltages have been simulated by using the PSCAD/EMTDC package. A comparison with a measured sag has been made, showing good agreement. The simulation results taught us that post-fault voltage sags mainly occur during faults in the MV networks. Strengthening the supply, or reducing the (post-fault) motor load are needed to solve this.