JD Engineering Works makes Hydro Turbine Alternators. The body of these alternators is made up of CAST IRON as we all know that iron is the strongest metal as compared to aluminum and others. The winding material is 100% made up of copper while the rotor has the superspecial neodymium magnet. These alternators can be provided at any RPM.
If you also want to purchase the same then contact JDEW as soon as possible.
More info:- Hydro Turbine Generator