Use of naturally occurring system disturbances to estimate the fault current contribution of induction motors

The contribution of induction motor loads to short-circuit currents can be significant and so must be considered when evaluating power system fault levels. Standard procedures for calculating short-circuit currents of induction motors require detailed machine data which may not be available. The Fault Level Monitor (FLM) was recently developed at EA Technology Ltd. to estimate network fault levels including the contribution from induction motor loads. Detailed information of the load or of the network is not required. The estimation technique is based on an analysis of the responses of the power system to naturally occurring disturbances which are recorded by the instrument. The FLM algorithm for predicting induction motor fault level contributions has been examined using simulation studies and comprehensive field tests at two industrial substations and a wind farm. Results are presented which show good agreement between the values obtained from the FLM and from conventional techniques