Unit 6 Turbine Vibration Investigation - Observation by PMT

Polar plot of IP and LP rotor when turbine load was 280 MW and worsen vacuum condition Out of phase pattern between bearing 3/4 and bearing 5/6 Bearing no. 3 Bearing no. 4 Out of phase pattern Bearing no. 5 Bearing no. 6

Compared to past record in Aug 04 Bearing no. 3 Bearing no. 4 Bearing no. 5 Bearing no. 6

LP bearing vibration increase Test 1 Throttle mode and control vacuum Throttle mode and normal vacuum LP bearing vibration increase

When go to worsen the vacuum, the vibration reduce significant Bearing no 5 & 6 vibration 280 MW 220 MW Vac 720 mmHg Vac 740 mmHg

Opposite vector effect between bearing no. 5X and 6X Phase shift position at high vibration Phase shift position at high vibration Low vibration position Low vibration position Opposite vector effect between bearing no. 5X and 6X when the vibration increase under normal vacuum Bearing no. 5 Bearing no. 6 Phase shift position at high vibration Phase shift position at high vibration Low vibration position Low vibration position

Rotor movement direction Bearing no. 6 Vector sum direction 6Y vector 6X vector B side LP rotor Vector sum direction 5X vector A side 5Y vector B side Bearing no. 5

Orbit plot show enlarged when vibration increased Bearing no. 5 Bearing no. 6

Past record in Aug 04 High vibration orbit Bearing no. 5 Bearing no. 6 Traditional phase pattern from technical paper Bearing no. 5 Bearing no. 6

Bearing no. 5 speed Vibration Run down Shaft centerline

Bearing no. 6 speed Vibration Run down Shaft centerline

Turbine vibration when bearing lube oil temp control changed +/- 2ºC LP vibration still appeared

after LP rotor balancing Run down on 11 April 07 No significant change in critical speed Run down on 07 April 06 after LP rotor balancing

LP rotor bearing vibration related to vacuum change Vibration was very sensitive to condenser vacuum change Vector effect direction of bearing no. 5 & 6 was opposite Out of phase pattern on IP and LP rotor as compared with past data Orbit show special preload symptom.