The paper presents the results of steady-state-stability investigations of a regulated electrical system, conducted to determine the best set of parameters of the voltage regulator from the view point of stability. The effects of the main-regulator-loop parameters, such as the gain and the time constants of the exciter, stabilising circuit and first-derivative control etc., on the stability of the system are examined. The method used in the investigation is the separation of domains, and the results are obtained in the form of stability regions, which define graphically the permissible ranges of the two adjustable parameters of the regulator. The calculations were conducted on a digital computer, and the system studied was a 2-machine system.