Stiffness factor and load angle

No, it is not related to electrical engineering.

Actually, Stiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom (DOF) when a set of loading points and boundary conditions are prescribed on the elastic body. It is an extensive material property.

Refer link:

http://en.wikipedia.org/wiki/Stiffness

May be this will help you.

Vinu_Answers Sure_Answers

The synchronous torque is some times called the Stiffness of the generator since as an oscillating system analogy (for the hunting analysis) it is analogous to the stiffness of a spring and the Moment of intertia is similar to the mass (Spring - mass analogy)

So now you can easily derive I hope

Torque from Synchronous Power and Synchronous Speed (rad/Sec)

Synchronous power from the load angles. Both the formulae must be well known to you.

Somewhat similar to the previous answer about generators, stiffness is sometimes used to refer to a power source whose voltage does not change much as higher current is drawn. It is an informal term (as far as I know). Examples are a generator running under low load (so there is plenty of reserve capacity, perhaps considered in terms of torque), or a transformer with low impedance, etc.