Air compressor Tripping problem at High Vibration 1

[Raju1980]

Dear All

kindly guide with your technical excellence and experience.


Compressor Manufacturer CAMERON
Model No TA-3000
Driven by motor of 421 KW
integrally geared 3rd stage compressor
having capacity of 3442 nm3/hr. (Rated)
Motor rpm 3555
1st stage pinion rpm 8880
2nd stage pinion rpm 16720 rpm
3rd stage pinion rpm 23150

Issue :-

We have two air compressor and one running and other as stand by.

During high air requirement, it will be up as around 4500 nm3/hr. and there is buffer tank able to meet plant requirement up to 30 minutes
Normally one compressor is running and other is in stand by

During normal running BOV valve is 18% open to atmosphere and system pressure is 8.47 bar g and motor current is 68 amps

During higher air requirement BOV close to 0% and current reaches to 80 amps FLC (79 amps) and system pressure reaches 7.47 bar g

Compressor B tripped first on first stage vibration high at that stage BOV was 0 % closed, indicating there was no antisurge action

during tripping the vibration value reached maximum range 127 microns whereas trip at 50.8 microns

since there was no other problem, mechanically replaced probe and now running ok

Now the problem started with Compressor A

first tripped on 1st stage vibration probe 101 then tripped on 3rd stage vibration probe 106 all showing 127 microns

first replaced a101 and started during higher consumption tripped on 106

Replaced probe 106 and now started tripped during initial loading at 1st stage vibration probe 102 the other probe in 1st stage

There is no more spare probe to replace, there was no indication of surging in any case.

Kindly guide , Thanks in Advance

 

[rotw]

Above you say that the trip settings are at 50 microns, but you monitor higher values.
So it means that values occurs during deceleration (after trip has been initiated) is this assumption correct ?

So maybe the reason for high vibration values is that during deceleration you will be passing through the 1st critical speed where there is vibration pick.

If this is the case, one should understand first why the machine exceeds its trip setting of 50 microns which initiates all the cascade of events.

Another point is that such problem seems common to two high speed shafts running essentially at different speeds. So what can be the common factor then. Do you have change in the oil supply temperature to the bearings ?

Another thing is to check the trip settings, but if the machine has been working fine for while that situation would look strange.

Also the trip voting philosophy is not indicated. If you have 1oo1 trip philosophy, any erroneous data will cause a trip for sure you safeguard even better the machine but causes economic losses. On 1oo2 or 2oo3 logic you have less spurious trips.

By the way, the fact that BOF valve is open 18% on normal operation is a bit strange in terms of design. Could you elaborate on this ?

 

[Raju1980]

Dear Mr.rotaryw

Thanks for your replies and quires, kindly find replies

Trip is at 50.8 microns and registered 127 microns during each trip, and which is the cause of trip, not coming during deceleration.

Compressor trip sequence may initiated once it reaches and functional check was conducted recently

Compressor was running as per the commissioned condition and there is no change done in any parameters.

Voting logic 1oo1 i as suggested by OEM .

BOV valve opens because very less requirement normally,550 nm3/hr. while rated is 3442 nm3/hr.

 

[rotw]

''Trip is at 50.8 microns and registered 127 microns during each trip''

That I don't understand.
If the trip setting is 50.8 microns, when this value is reached the trip shall be immediately initiated, so how come you reach/measure 127 microns at the same speed ?

 

[Raju1980]

''Trip is at 50.8 microns and registered 127 microns during each trip''

This is thereason we were suspected probe related issue and change two probes checked all wirings, now thi is shifted to other probe

 

[rotw]

"BOV valve opens because very less requirement normally,550 nm3/hr. while rated is 3442 nm3/hr."

Assuming no IGV, fixed speed drive, normally BOV valve open to keep the operating point within the compressor curve.
It should be set to position the operating point on the control line.
If you are on pressure control, than the BOV will continue to open and increase the capacity till you reach the desired set pressure.

Is there a possibility that rotating stall exists in your operating range?
Rotating stall is not necessarily along the surge line but can be anywhere within the operating range and can originate unwanted vibrations.

 

[Raju1980]

There is IGV and which is in auto, but during low load requirement the BOV was normally observed as open 18% for both compressors even at that stage minimum current is reached, may be the reason for opening BOV

The trip happeneed at two different loading conditions during starting of loading and during very high loading, that indicate less chance for stalling,

anyway how can identify stalling if exists

Thanks for your valuble updates

 

[bcs5274]

check supply voltage to sensors