Vibration Data of C-2800B Machine Details - 3 Stages integrally geared compressor is driven by turbine. (Normal turbine speed is 3000 rpm) - There are LP rotor with 1st, 2nd stage and HP rotor with 3rd stage - There is vibration protection system on each rotor. (1 proximity probe/shaft, located at each pinion rotor) Warning and danger limits are 40 and 60 um p-p respectively.

LP Rotor Pinion Teeth = 23 Vibration probe is placed in 1

st

stage side. - 1

st stage: No. of blade = 16

- 2nd

stage: No. of blade = 15

Main Gear Gear teeth = 379

HP Rotor Pinion Teeth = 16 Vibration probe is placed in 3

rd

stage side. - 3

rd stage: No. of blade = 14

Event 1. HP rotor was replaced new counter weight and balanced. The balancing report showed good result.

2. After test run (No supplied air load), machine was tripped by high HP rotor vibration over 60 um p-p when turbine’s speed was over 2350 rpm. But LP rotor vibration is rather normal.

VI2830B1.PV

VI2830B2.PV

0.66

um

FI2830B.PV

20-Feb-15 3:10:00 PM20-Feb-15 1:50:00 PM 1.33 hours

Plot-0

0

10

20

30

40

50

60

701000 1400 1750

Speed of Turbine (RPM)

2000 2350

Speed was increased over 2350 rpm. Then, machine was tripped.

HP rotor

3. We can collect the shaft vibration data through 3500 rack and SKF Microlog in each speed. The time wave form and spectrum will be showed in the next page. Discussion: 3.1 Vibration was high by 1X HP rotor speed significantly that indicate many of malfunctions. 3.2 HP rotor vibration was increased rapidly after turbine’s speed had been changed from 2000 rpm to 2350 rpm. 3.3 When turbine’s speed was held at 2350 rpm, HP rotor vibration was rather fluctuated. 3.4 There were some sub-synchronous frequencies in HP rotor spectrum while turbine’s speed was 2350 rpm. Spectrum show 0.314x and 0.686x of HP rotor speed.

3.5 We collected casing vibration data in HP rotor side through SKF Microlog. The vibration result showed that overall vibration is higher than before (normal vibration). Spectrum showed 1X of HP rotor speed and harmonics like rotor had more precession in casing. 4. After test run, machine was inspected. There are no abnormal like rubbing, foundation looseness, casing distortion and all mechanical parts are in good condition.

VI2830B1.PV

1.11

um

VI2830B2.PV

FI2830B.PV

20-Feb-15 3:10:00 PM20-Feb-15 1:50:00 PM 1.33 hours

Plot-0

0

10

20

30

40

50

60

70 1000 1400 1750 2000 2350 LP rotor

Speed of Turbine (RPM)

LP Rotor - Turbine’s speed is 1000 rpm

- Turbine’s speed is 1400 rpm

- Turbine’s speed is 1750 rpm

- Turbine’s speed is 2000 rpm

- Turbine’s speed is 2350 rpm

HP Rotor - Turbine’s speed is 1000 rpm

- Turbine’s speed is 1400 rpm

- Turbine’s speed is 1750 rpm

- Turbine’s speed is 2000 rpm

- Turbine’s speed is 2350 rpm

Possible causes: 1. HP rotor was run near critical speed ? In my opinion, the rotor which was replaced new counter weight and balanced are in the same design and mass. So, critical speed may not be changed too much. Now, rotor dynamics was calculated for confirmation. 2. For good balancing, from eq. [synchronous response motion = unbalance force/synchronous dynamic stiffness]. Are there some problem with synchronous dynamic stiffness ? (such as oil pressure or temperature) In my opinion, the bearing clearance, oil pressure and temperature are in the same condition. It is low possibility. 3. There are some fluid induced instabilities at HP rotor ? For turbine’s speed is over 2000 rpm, there are fluctuated vibration at HP rotor. And spectrum at 2350 rpm showed sub-synchronous frequencies but wasn’t around 0.4-0.48x that indicated this problem. So, this possible cause is low too. Questions: 1. From my possible causes, do you have any possible cause of this problem ? 2. Machine diagnostic by one proximity probe per shaft is hard. How do you think about this diagnostic ?