For lagging power factor = (IR*cosφ + IXsinφ)/V_r For leading power factor = (IR*cosφ - IXsinφ)/V_r Zero voltage regulation occurs on leading power factor only.
Frequency of natural oscillation is given by, fn = {((dPe/dδ)at(δo))/M)} dPe/dδ = ((V1*V2)/X*(cosδ)) = (11/05)*cosδ = (11/0.5)*0.5 M = (H*s)/(πf) = 4/(50π)