PURPOSE: To prevent a generator from its damage by constituting a device of current transformers for detecting each load of three phases, current arithmetic devices for calculating a deviation between a detected current of the current transformer and the rated current and power regulators for distributing each phase current to a load regulating heater by a deviation value signal from the current arithmetic device.

CONSTITUTION: Rotation of a rotary shaft in a water turbine 1 is accelerated through a step-up gear 2 and transmitted to a generator 3, and power is supplied to single-phase loads RS, ST, RT connected to each phase of the generator 3. Each phase current, detected by a current transformer 5 provided in each phase, is input to a current arithmetic device 6 provided in each phase, and a deviation value between each phase current and the rated current is comparison-calculated in this current arithmetic device 6 where signal conversion is performed. A proportional-plus-integral control of the deviation value, output from each current arithmetic device 6, is performed by each power regulator 7, and balance of power in each phase can be held by regulating a value of currents U, V, W fed to a heater 4.