Abstract: According to one embodiment, there is provided a variable-speed operation control apparatus of a hydroelectric power generation system including a power generator interconnected to a power system through a main circuit and a water turbine directly connected to the power generator. The apparatus includes a branch circuit branched from the main circuit and including a frequency converter which performs conversion between an output frequency of the power generator and a system frequency of the power system, wherein the power generator is interconnected to the power system through the branch circuit when a flow rate of water is less than a fixed level.

Abstract: A rotary electrical machine structure support that can have strength high enough to endure vibration and strain while suffering less defects, deformation, peeling, and breakage is manufactured. A method of manufacturing a rotary electrical machine structure support includes: an arranging step of arranging a first joining object member and a second joining object member composed of stacked and integrated plate materials and thicker than the first joining object member, with their end parts in contact with each other; and a joining step of making a rotary driven tool penetrate into a boundary part between the first and second joining object members whose end parts are in contact with each other, from a first outer surface side of the boundary part, and sliding the tool along an interface of the boundary part, whereby a rotary electrical machine structure support composed of the joined first and second joining object members is obtained.

Abstract: According to one embodiment, there is provided a variable-speed operation control apparatus of a hydroelectric power generation system including a power generator interconnected to a power system through a main circuit and a water turbine directly connected to the power generator. The apparatus includes a branch circuit branched from the main circuit and including a frequency converter which performs conversion between an output frequency of the power generator and a system frequency of the power system, wherein the power generator is interconnected to the power system through the branch circuit when a flow rate of water is less than a fixed level.

Abstract: A method of manufacturing a rotor coil of to an embodiment includes preparing a wire strand bundling a plurality of wires and a reinforcing member configured to reinforce the wire strand; arranging the wire strand and the reinforcing member to bring an end of the wire strand and an end of the reinforcing member into contact with each other, the wire strand being arranged to have a longitudinal direction perpendicular to a boundary between the wire strand and the reinforcing member and to include the plurality of wires with an inclined longitudinal direction thereof on a first outer surface inclining with respect to the longitudinal direction of the wire strand; rotary driving a tool at the boundary on the first outer surface so as to enter the boundary; and moving the rotary driven tool on the boundary along the first outer surface.