Direct axis sub-transient reactance (Xd”) is the quotient of the initial value of a sudden change in that fundamental AC component of armature voltage, which is produced by the total direct-axis armature flux, and the value of the simultaneous change in fundamental AC component of direct-axis armature current, the machine running at rated speed. Saturated values are calculated by applying a short circuit to a machine operating at rated open circuit voltage. Saturated values are calculated by applying a short circuit to a machine operating at rated open circuit voltage
