Lateral Critical Speed Analysis

Engineering

DynoMech undertook the analysis of a direct-drive 33MW turbine-generator (TG) unit of 3000 rpm, where, upon replacing the generator, vibrations of the order of 10 mm/sec and above were observed. High vibration levels were observed at Bearings #3 (LP Rotor Front End), # 4 (LP Rotor Rear End) & 5 (Generator Rotor Front End). These vibrations caused the TG set to run at less than its maximum output.
The 33 MW TG Unit was a direct drive system and hence called for a detailed rotor-dynamic analysis. Safety margins in terms of resonance frequencies, amplification factors, damping ratios, logarithmic decay and stability established for each Individual rotor would not be sufficient to ascertain a safe vibration limit of the direct drive TG Set since the three rotors (HP, LP & Generator) were coupled directly and would give rise to coupled vibrations which would often lead to lesser safety margins or resonance criteria.

 

Lateral Critical Speed Analysis of 33 MW Direct Drive Turbine-Generator Unit
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