METHOD OF PROTECTING WATER TURBINE

PURPOSE:To protect a water turbine against resonance, by actuating brake in cast that oscillation frequency stands within a critical resonance zone for more than a predetermined time, and thereby bringing the oscillation frequency out of the critical resonance zone. CONSTITUTION:When starting instruction is given, a by-pass valve 8, down- stream seal ring 9 and main valve 7 of the inlet valve are opened in this order, and guide vanes 4 are once kept at its no-load opening. Subsequently, when the speed of rotation of a runner 1 is increased gradually with opening of the guide vanes 4 and reaches a level corresponding to the lower limit value of a critical resonance zone, a time-limit relay is energized. Here, in case that the speed of rotation is still lower than a value corresponding to the upper limit value of the critical resonance zone even after passing of a tolerable time period, operation of the water turbine is stopped immediately by lowering the speed of rotation by impressing generator brake and thereby bringing the speed of rotation out the critical resonance zone.