Switchgear Short Circuit Rating Studies
This Power Station was designed in the 1970’s when the fault current contribution made by induction motors into short circuits was not widely recognised. The main HV switchboard was supposed to accommodate up to 180 MW of connected generation. Calculations undertaken when installed capacity reached 125 MW, showed the fault level had increased beyond the switchgear’s short circuit making and breaking capabilities. AEE was engaged to independently review the software model of the power system and re-run the short circuit studies. This was done and the results were confirmed.
AEE developed options for restoring safe operations to the power station HV switchboard. These included the use of neutral earthing resistors, neutral earthing switches, fault current limiting reactors and high speed current interrupters.
AEE conducted load flow, short circuit and motor starting studies to assess the efficacy of each option. The aim of each study was to ensure adequacy of the power station plant, not only during normal operations, but also during planned and unplanned plant outages.
The preferred solution was fault current limiting reactors in series with resistors. This arrangement successfully attenuated both the AC and DC components of short circuit current to within switchgear ratings.
AEE continued working on the protection scheme designs and protective device settings to ensure that the project achieves all of its objectives.
This is the second affordable and effective fault current limitation system AEE has engineered at this client’s power stations.