A power coupler for transferring rotary power from a rotary power device to a load device includes a shear thickening fluid (STF) and a chamber that contains the STF. The power coupler further includes a drive shaft housed radially within a drive side section of the chamber and protruding outward from an end of the chamber for coupling to the rotary power device. The power coupler further includes a load shaft housed radially within a load side section of the chamber and protruding outward from another end of the chamber for coupling to the load device. The power coupler further includes a drive turbine housed radially within the drive side section and coupled to the drive shaft. The power coupler further includes a load turbine housed radially within the load side section at a fixed operational distance from the drive turbine and coupled to the load shaft.

Systems, methods, and devices are provided to generate a stable supply of electrical power in a drill string. In one example, a downhole turbine generator includes a turbine, a speed governor, and an alternator. The turbine may transform hydraulic power of a first fluid medium into rotational power of a rotating shaft. The speed governor may reduce the rotational power of the rotating shaft in a variable amount that depends on the speed of the rotating shaft. Specifically, weighted arms may shear a second fluid medium more when the speed is higher and less when the speed is lower. The shearing of the second fluid medium may generate a countervailing torque on the rotating shaft to reduce the rotational power of the rotating shaft. The alternator then may produce a generally stable supply of electrical power from the rotational power of the rotating shaft.

Systems, methods, and devices are provided to generate a stable supply of electrical power in a drill string. In one example, a downhole turbine generator includes a turbine, a speed governor, and an alternator. The turbine may transform hydraulic power of a first fluid medium into rotational power of a rotating shaft. The speed governor may reduce the rotational power of the rotating shaft in a variable amount that depends on the speed of the rotating shaft. Specifically, weighted arms may shear a second fluid medium more when the speed is higher and less when the speed is lower. The shearing of the second fluid medium may generate a countervailing torque on the rotating shaft to reduce the rotational power of the rotating shaft. The alternator then may produce a generally stable supply of electrical power from the rotational power of the rotating shaft.

A hydrodynamic retarder includes: a retarder chamber in which a rotor and a stator are arranged, the rotor and the stator together forming a working chamber for being filled with and emptied of a working medium; a working medium tank, which includes sump, storage, and expansion regions, the sump region and the storage region for accommodating the working medium that is not currently in working chamber; a filling channel for supplying the working medium into the working chamber, the filling channel being a tube including an inlet opening and an outlet opening; a return channel for discharging the working medium from the working chamber; a rotor housing; a stator housing; a tank housing; and an inlet chamber, the inlet opening terminating in the working medium tank, the outlet opening terminating in the inlet chamber, the inlet chamber being formed by the stator housing and the stator.

A hydrodynamic retarder includes: a retarder chamber in which a rotor and a stator are arranged, the rotor and the stator together forming a working chamber for being filled with and emptied of a working medium; a working medium tank, which includes sump, storage, and expansion regions, the sump region and the storage region for accommodating the working medium that is not currently in working chamber; a filling channel for supplying the working medium into the working chamber, the filling channel being a tube including an inlet opening and an outlet opening; a return channel for discharging the working medium from the working chamber; a rotor housing; a stator housing; a tank housing; and an inlet chamber, the inlet opening terminating in the working medium tank, the outlet opening terminating in the inlet chamber, the inlet chamber being formed by the stator housing and the stator.