It has been recognised that the dynamic-stability margin of synchronous generators can be improved by the damping effect of the speed-stabilising signal in the excitation control system. The dynamic-stability analysis is extended to account for the effect of loads modelled as a nonlinear function of voltage. In order to make the analysis realistic, a conventional load-frequency control system is also considered to be regulating the power-system frequency and tie-line power. The load voltage is considered to be undergoing changes in the dynamic period in response to speed signal in the excitation system which establishes a coupling betweenQVand p.f. control loops. The damping effect on frequency and tie-line power oscillations is studied by varying the load characteristics and excitation stabiliser parameters.