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Thrust Bearing - Steam Turbine

04/19/2017 9:46 AM

I need help to solve a problem

- steam Turbine 350MW, main steam temperature 538°C.

we had a problem in the thrust bearing of turbine, the alarm temperature is 99°C and trip 107°C...

we have 2 sensors in each side of thrust bearing... the generation was in 290MW and the temperatures was 93°C in 1 sensor... in 2 minutes the temperature raises to 97°C and after that, in 10 seconds the temperature raises to 113°C... the other sensor was 87°C and raises until 97°C (in the same side), so we had a trip from turbine.

now, we can't inspect the bearing, because we need to wait that the temperature of the metal from turbine comes down... could anyone give me a light about what happened?

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#1

Re: Thrust Bearing - Steam Turbine

04/19/2017 11:04 AM

Check all these issues....

https://canteach.candu.org/Content%20Library/20042414.pdf

....report back....

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#11
In reply to #1

Re: Thrust Bearing - Steam Turbine

04/20/2017 1:34 PM

you can even cheat and search on 'Thrust' to get to the good stuff...

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#13
In reply to #11

Re: Thrust Bearing - Steam Turbine

04/20/2017 1:57 PM

Then there is this .pdf (dates to circa 1975, so it is probably old enough to matter), as the basic principles have not changed.

TAMU tilt plate thrust bearing paper 1975?

#1 Lesson: Do not exceed the design envelope of speed and thrust.

#2 Lesson: Maintain optimal oil pressure and quantity, and maintain optimal oil quality. (this includes keeping water out of the oil, BTW).

#3 Lesson: refer back to #1 and #2 if still confused.

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#2

Re: Thrust Bearing - Steam Turbine

04/19/2017 2:57 PM

Lubrication?

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#12
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Re: Thrust Bearing - Steam Turbine

04/20/2017 1:49 PM

Overrated.

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#3

Re: Thrust Bearing - Steam Turbine

04/19/2017 3:05 PM

Now the turbine has cooled down enough to examine the bearings and associated bearing supports, cooling systems, etc what have you found out?

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#4

Re: Thrust Bearing - Steam Turbine

04/19/2017 3:58 PM

It would be uneconomic to do so. If supplementary lighting equipment is required, it is best sourced locally.

What happened is that the control system worked correctly to protect the equipment from damage due to an over-temperature condition.

It is amazing how many individuals would rather ask a bunch of complete strangers about such things over the internet than pick up the telephone and talk to the equipment manufacturer directly. No. Not amazing. Staggering would be a better word.

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#5

Re: Thrust Bearing - Steam Turbine

04/19/2017 4:00 PM

Did anyone hear any sharp, loud noises near the turbine exhaust? Maybe you pulled too much vacuum, caused insufficient back-pressure, and got condensation in the final stage of steam turbine. This, as I recall, can result in loss of material by impingement, and will upset the thrust balance point of the turbine, resulting in rapid heating of the thrust bearing with trip.

At the minimum, you should go over the logs, or sequel server, and find out what happened operationally right before that. If vibration monitors are present, did you get any vibration alarms?

Inspection: Visually or bore scope examine the exhaust stage of the LP turbine. Look for new spalling, missing metal, etc.

What happened to thrust bearing oil pressure during these events? You need to examine that as well.

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#6

Re: Thrust Bearing - Steam Turbine

04/20/2017 12:58 AM

when ever thrust bearing increases,check the following:

1.bearing load increases or not by checking shaft axial position is there any movement (for example +/- 0.6 mm is the alarm setting value) is that shaft moving in normal / counter position to ensure the increase of bearing load.so first rule out the increase in temp is due to bearing load.

2.check the lube oil temp and pressure are they with in limits.

3.check the cooloing water temp and pressure are they with in limits.

4.then ask instrument dept to check the RTD sensor

RTDs can have two, three, or four leads. In a two-wire configuration, simply connect the meter across the leads and measure the resistance. For a PT-100 RTD at room temperature, this should be about 110 Ω (±20%). If you grab the tip of the RTD, you should see the resistance increase. Let go, and you should see the resistance gradually settle back after you release the tip.in your case check both sensor ie sensor which gave trip as well as sensor which gave 87 deg C.out of both which one is wrong.if both are correct as per inst dept check, then reduce turbine load or speed and check the bearing temp is also reduce according to load and speed.

If load and speed is less still temp increase is observed then replace the both the RTD.

even after replacing both RTD still temp increase observed it is due to varnishing effect taken palce at RTD sensor area. SO CHANGE THE LOGIC setting to 2 out 2 trip setting instead of 1 out 2.

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#7

Re: Thrust Bearing - Steam Turbine

04/20/2017 9:09 AM

I will assume the bearing or the shaft has some sort of cooling? probably water cooled. check that the cooling system is working.

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#8

Re: Thrust Bearing - Steam Turbine

04/20/2017 10:29 AM

Yes, also check for coolant blockage on the side with higher temperature, when testing things.

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#9

Re: Thrust Bearing - Steam Turbine

04/20/2017 11:39 AM

Dear Member,

The reasons could be

1. Improper sensor, cable. Wrong calibration

2. Some blockage in quantum of oil surrounding the sensor - which will allow temp. to shoot up.

3. A portion of oil by-pass the sensor which makes to accumulate heat in that zone and cause problem.

It is not advisable to re-start the turbine with out opening and inspection and sort out the issue.

Otherwise the damage may be catastrophic

DHAYANNADHAN.S

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#10
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Re: Thrust Bearing - Steam Turbine

04/20/2017 11:49 AM

I can agree with everything except the usage of the word "quantum", I think dhayanandhan meant the smallest volute, or smallest volume of based on the Latin root meaning of the word, as this is nothing to do with quantum in the modern context.

Not to be nose picking, but that is certainly an interesting booger.

Figure out (1) what was the history of all recorded data

(2) what is the status of all instrument associated, are they correct?

(3) is there metal in the oil now

Then you will have scratched the diagnostic surface, and may have to delve (dig) deeper to find the truth.

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#14

Re: Thrust Bearing - Steam Turbine

04/20/2017 2:34 PM

- The oil temperature did'nt change (we have sensor - Thrust return oil temperature)

- The pressure of oil didn't change

- The axial position was in +0,2mm, in the moment of trip it goes to -0,4mm, (I think it's ok, because the bearing load goes down in the moment of the trip - Governor valves and Stop valves close)

- We have two sensors in the same side , both increase temperature in the seconds before trip until trip. one more than other

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#15
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Re: Thrust Bearing - Steam Turbine

04/20/2017 2:43 PM

Then you best start looking for whatever increased the thrust load on that bearing right before the trip. I think you are in for a complete inspection of rotor, blading, and diaphragms. Also look at the other bearings to make sure they are not showing signs of machine misalignment.

How was heat rate looking in the days prior to the trip? Any noticeable changes? Hours before? Every piece of data you can pull up right now is your friend.

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#16
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Re: Thrust Bearing - Steam Turbine

04/20/2017 2:50 PM

In the other bearings - 6 journal bearings - everything ok, we didn't have changes..

Some days before it happens, The eccentricity becomes high and we think that the problem was the sensor.. But maybe it wasn't the sensor of eccentricity..

Maybe the eccentricity was really high

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#17
In reply to #16

Re: Thrust Bearing - Steam Turbine

04/20/2017 2:58 PM

See what I mean? Sometimes we tend to write things off as nonsense, when the real message is the real message.

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#18
In reply to #17

Re: Thrust Bearing - Steam Turbine

04/20/2017 3:22 PM

but what can cause a problem to increase the eccentricity?

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#19
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Re: Thrust Bearing - Steam Turbine

04/20/2017 5:03 PM

Have you checked the sensor and its mount?

Is your sensor mount loose or structure the sensor mount is mounted to perhaps flexing? Perhaps a foundation issue? Perhaps this is the source of the increased eccentricity measured.

Best to confirm the sensor is functioning correctly before looking at the bearings in too much depth.

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#20
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Re: Thrust Bearing - Steam Turbine

04/20/2017 6:29 PM

in what plane and relative to what is the eccentricity? Thrust bearing or shaft?

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#21

Re: Thrust Bearing - Steam Turbine

04/22/2017 10:40 AM

How old is the unit? What means or method is used to control the lube oil quality? Do you filter and centrifuge the lube oil to remove water or just filter? Do you send out samples to insure proper lubricating properties of the oil? Eccentricity due to excessive wear on the journal bearings from poor oil properties can result in rotor clearances changing prior to making contact and resultant catastrophic failure. Would think that they would change more slowly than you indicated though. If it is a Kingsbury type thrust bearing, failure of an individual shoe might cause a rapid indication as you mention. What type thrust bearing is it?

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#22

Re: Thrust Bearing - Steam Turbine

04/22/2017 7:29 PM

Google feed water effect on steam turbine thrust?

https://www.google.com.au/search?q=turbine+feed+water+effect+on+turbine+thrust&rlz=1T4GGHP_enAU411AU411&site=webhp&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjM_OztmrnTAhUJF5QKHWKkCjsQsAQIJg&biw=1152&bih=493#spf=1

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#23

Re: Thrust Bearing - Steam Turbine

04/23/2017 12:03 PM

A few unanswered questions. What were the unit conditions prior to the trip; constant load for minutes/hours/days, load following, ramping up/down, sudden load shifts, changes in steam inlet/turbine outlet/condenser backpresssure conditions, etc., etc.

Since it's unlikely that you had multiple sensor failures (that's why you have multiple trip inputs into redundant protective systems), then you should be looking at what would cause the turbine shaft to unexpectedly grow laterally, or perhaps bow due to uneven temperature differentials across the shaft/casings.

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