During operation of at least one power generator (EE) in a power supply network, a reactive power transfer between the two upper voltage levels (1, 2) is sensed at a first transformer (T1) connecting these levels, and the voltage at a first network connection point (5) at the lowest voltage level (3) is ascertained. The amount of a reactive power demand served by the power generator (EE) is calculated as a function of the ascertained voltage value in order to maintain the voltage ascertained at the lowest voltage level (3) within a predefinable voltage range, wherein a means (WR) of the power generator (EE) is activated for a reactive power draw or a reactive power delivery, based on the calculated reactive power demand.