The robust transient stability problem of a synchronous generator in an uncertain power network with transfer conductances is addressed. A robust adaptive nonlinear feedback control algorithm is designed on the basis of a third order model of the synchronous machine: only two system parameters (synchronous machine damping and inertia constants) along with upper and lower bounds on the remaining uncertain ones are supposed to be known. The conditions to be satisfied by the remote network dynamics for guaranteeing L 2 and L ∞ robustness and asymptotic relative speed regulation to zero are weaker than those required by the single machine-infinite bus approximation.