Is it necessary to change the existing shaft alignment (catenary) to cater for a Retrofit ?
The Alstom alignment philosophy for new units is to set all bearings on the rotor natural catenary i.e. at all couplings the coupling gaps are parallel. When changing from shrunk-on disc LP rotors to the much stiffer Alstom welded rotors, the natural catenary is significantly different and re-aligning the complete unit to suit the new catenary would be a major undertaking requiring large bearing/pedestal, generator and exciter moves. This would, of course, have significant program and cost implications. Our experience shows that it is often possible to stay with the original shrunk-on disc catenary, provided this is known at the design phase and rotor stresses and bearing loads are confirmed as acceptable. Minimizing alignment changes is a particularly important part of the ‘design for installation’ process since alignment changes will have major impact on the installation duration and cost.
