Abstract:

An alloy steel flywheel with 60 MJ storage energy at 2700 r/min rated speed was designed in this study, in order to achieve MW-level power output in the flywheel energy storage device of drilling rig power system. 35CrMoA steel was the selected material and manufactured into ‘H’ cross-section. The flywheel was 1600mm in diameter, 380mm in thickness and weighed 4000 kg. The core shaft was interference fitted with the hub locally to repeal assembly difficulty. While several cylindrical pins transferred the torque between flywheel and shaft instead. Finite element method (FEM) analysis evaluated these design ideas efficiently. The spoke formed thick inner and thin outer accorded with equal-strength design approximately. Besides, thicker flange benefitted to adjust mass distribution for larger rotary inertia. And the pins connection to transfer torque optimized local stress compared to traditional spline connection. The maximum stress in flywheel shafting system, owning 2.5 times' safety coefficient, was less than 500 MPa under the rated rotary speed. Flywheel energy storage (FES) device was debugged successfully in March 2016 with the energy density of 4.17 W·h·kg^-1 and the secific power of 250 W·kg^-1, achieving the functions of 150～200 kW charging and 500～1000 kW discharging. This project indicated that our country obtained the ability to develop a sigle FES equipment with MW-leveled power output.

Key words: flywheel energy storage system (FESS), alloy steel, keyless connection, FEM