Abstract: A circuit arrangement, for deriving, from sensed power variations in a network, a signal for supplying the exciter of at least one synchronous machine coupled to the network, includes first and second vector identifiers, each providing a direct and phase-shifted output with each of the outputs coupled through an impedance matching amplifier to a summing junction. The direct signal from the first vector identifier and phase-shifted signal from the second vector identifier are conducted to one summing junction and the phase-shifted output of the first vector identifier and direct output of the second vector identifier to a second summing junction, with the outputs of the two summing junctions summed at a further summing junction after being coupled through additional impedance matching amplifiers to result in a total signal at the output of the third summing junction which varies in a mathematically positive sense with increasing oscillation frequency.