Short Circuit Ratio or SCR is a measure of Stabilty in Synchronous Generator. It is a Ratio of Field Current required to produce Rated Voltage and Field current required to produce Rated Short Circuit Current.
It is normally determined graphically.
Derivation of SCR is given in this Video. It is found to be 1/xdpu where xdpu is per unit Synchronous Reactance. Thus SCR is inversaly proportional to Synchronous Reactance.
Maximum Power increases with high SCR. Stabilty Margin is the difference between Maximum Power and Rated Power and hence it increases.
High SCR increase Synchronising Power of Generator. Thus the Generator synchronises fast after disturbance.
High SCR improves Volatage Regulation.
However Short Circuit Current increases with high SCR.
SCR can be increased with higher Air Gap but cost of the Generator increases
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