ABSTRACT
This troubleshooting case study involves the massive failure of a large 700 MW (one million horsepower) steam turbine generator set initiated by the detachment of a large low-pressure turbine blade at running speed 3600 rpm. As part of the resulting post-accident failure investigation, the author's nonlinear rotor vibration simulation-model analyses uncovered why the blade-detachment large rotor unbalance triggered a destructive high level of rotor vibration that completely destroyed the machine. The root cause discovered by the author was rotor vibration subharmonic resonance that was thus discovered to be an intrinsic characteristic of fixed-arc journal bearings under very large rotor unbalance forces. The author's simulations also clearly show, in contrast to fixed-arc journal bearings, that pivoted-pad journal bearings do not intrinsically make matters worse since they almost totally squelch the dominating subharmonic vibration component greatly amplified by fixed-arc journal bearings. This finding was not welcomed by the steam turbine generator manufacturer since their entire employment of large low-pressure steam turbines in their customers’ power plants used fix-arc journal bearings. That fact accounted for the considerable controversy that arose when the author first published his findings on this in 1980, with color photographs of the failed machine, also presented in this chapter. The most compelling motivation for the author to publish his findings was the associated danger to power plant operating personnel when such a large running machine disintegrates with more kinetic energy than a 100-car freight train traveling at 70 mph.
