Abstract: A system for protecting a turbine-generator power plant governed by signals representative of turbine mechanical power and generator electrical power to reduce at times the turbine mechanical power, with an electronic filter included therein for the purposes of filtering a periodic time varying component of the electrical power signal having a response time within adequate protective limits, is disclosed. More specifically, the electronic filter generates a train of fixed time durations wherein during each fixed time duration the maximum and minimum amplitudes of the electrical power signal are selected. A signal is sampled at the end of each fixed time duration and held constant for each next fixed time duration, said signal being representative of the average of the maximum and minimum amplitudes selected during each fixed time duration.