Generator Short Circuit Ratio

The rating power of the generator in kva.

Generator short circuit ratio. Short circuit current decrement curve not required but will be useful in relaying time calculations x 0 zero sequence reactance used in unbalanced fault calculations for grounded generators one item not supplied as part of the generator nameplate or data sheet that may be required for relaying time calculations is the type of voltage regulator used with the generator. It is the ratio of field current required to produce rated armature voltage at open circuit to the field current required to produce the rated armature current at short circuit. Significance of short circuit ratio scr short circuit ratio is an important factor of the synchronous machine. Where the scr is above 1 a grid has good grid strength and will be less.

It affects the operating characteristics physical size and cost of the machine. A higher scr makes the machine inherently more stable with less excitation but results in a more expensive machine design. The short circuit ratio scr is different than the x r ratio. The scr can be calculated for each point on a grid.

Short circuit ratio can easily be obtained from the open circuit occ and short circuit characteristics scc of synchronous machine. A lower scr requires a better excitation system to preserve stability but allows a smaller less expensive generator design. The large variation in the terminal voltage with a change in load takes place for the lower value of the short circuit ratio of a synchronous generator. Short circuit ratio relates to excitation requirements for stable operation.

The short circuit ratio is used to show the strength of ac system if scr is low it means weak ac system. Consider now the power source being a synchronous brushless ac generator alternator. The rated phase to phase voltage of the generator in v. However circuit breakers are typically tested at certain x r ratio depending on type of application.

3ph 2ph or 1ph short circuit conditions and the supplied. Which is a measure of the generator stability characteristics. The short circuit impedance of the generator as a percentage. For generator applications the sc ratio is the reciprocal of the synchronous reactance xs scr 1 xs.

The value of short circuit ratio varies from 0 5 to 0 8 for turbo generator 1 to 1 4 for hydro generator and 0 4 to 0 5 for synchronous condenser. The generator short circuit fault current calculator uses a simplified method to calculate the fault current from the following parameters.