# Low Seismic Vibration vs High Displacement on Bearing 1 of PGT10 Gas Turbine

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#### bkarim55

Dear All,

PGT10 is a double shaft HDGT driving 10MW power generator. The journal bearings used on the HP (10.800RPM) and LP (7.900RPM) rotor are of tilting-pad type. This machine is equipped with Bently Nevada monitoring system and a seismic probe is installed on the top cover of the 1st and 4th bearing.

On Mark V; the seismic vibration reading on bearing 1 is about 3 mm/s which is a low and quite value. But the displacement reading looks a little bit higher than it should be for both X and Y probes.

On Bently Nevada; Actual overall values (displacement micrometer peak To Peak) are: X = 95 microns and Y= 93 microns. The readings what we used to have are: X= 46 and Y= 44 microns.

One more thing; the metal temperature of bearing 1 is higher than the others 3 bearings.

Someone help me to understand what's happening on this tilt-pad bearing 1?

#### glenmorangie

Sure looks like you have developed some kind of problem.

1) What is the bearing Temp.?

2) Can you put a vibration analyzer on the bearing and see what the predominant frequency of the vibration is?

This will at least give us a guide to whether this is unbalance or alignment.

When did this happen? Did it happen suddenly or progressively? Please give as much information as you can get.

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#### bkarim55

Dear Glenmorangie

> 1) What is the bearing Temp.?

The vibrations and temperatures readings have been done under the following running conditions: Power = 2.0 MW, TNH = 94.53%, TNL = 100.55%, LubeOil Header = 1.67 bar/38Â°C and Inlet ambient = 09Â°C.
RTDs are installed on the 2 lower tilting-pads of each bearing and the readings of the bearing metal temperatures are (2 RTDs are faulty xx): Bearing1 = 73/66Â°C Bearing2 = 60/58Â°C Bearing3 = 66/xx Â°C and bearing4 = 59/xx

> 2) Can you put a vibration analyzer on the bearing and see what the predominant frequency of the vibration is?

Synchronous frequency is predominant. First probe: 1X = 84.16, 2X = 1.03, 3X = 0.74. For the second probe: 1Y = 80.16, 2Y = 2.40, 3Y = 0.62 (micrometers peak to peak).

> 3) When did this happen? Did it happen suddenly or progressively?

This happened after a MI (Major Inspection). During Mi, the 4 bearings replaced with new OEM Genuine Parts and the HP rotor has been replaced by another refurbished rotor (not the one removed). This rotor (the refurbished one) has been sent to the contractor shop (who did the MI) for repair and shop balancing. The 3 first stages blades of the axial compressor and the HP buckets have been replaced during repair/balancing shop.

When MI finished and StartUp crazy vibrations! Seismic vibrations trend show a cyclic fluctuation between 8 and 18mm/s and displacement over 200microns. Trim balancing is carried out and the vibrations decreased at seismic 3.3 mm/s and displacement about 90 microns on bearing1. THIS 90 MICRONS SEEMS TO ME HIGHER. We used to have 40 to 45 microns before the MI.

Question about the forum! Time to time a photo or chart can explain better than thousands of words.. What about to add something like files attachment in this forum?

Let me know if more details are required.

Many thanks in advance and Best regards,
Karim

#### glenmorangie

Thanks for the detailed reply. It kind of looks like you still have some imbalance. Really it would take a further trim balance to be sure. Although your running level is higher than before the MI, you could live with it with some careful monitoring.

If you load up more, what happens?

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Dear Karim,