The paper examines the behaviour of an isolated a.c. turbogenerator system connected to an infinite busbar, in which the conventional voltage regulator of the generator has been replaced by a minimum-variance self-tuning regulator. Simulation studies are presented employing a well-tested and representative non-linear model of the system. The regulator adapts successfully to variations in the non-linear system dynamics, caused by substantial changes in operating conditions and also in system configuration. Performance is rigorously assessed in terms of dynamic stability boundaries and also transient stability boundaries arising from balanced three-phase faults at the generator transformer.