GT Driving Centrifugal Compressor


GT drives Centrifugal compressor, any possibility without running the GT the reverse rotation can be happen from load compressor side to turbine?

I have face a problem, without starting GT I got the rpm from speed sensor and bearing #1 & #2 radial vibration. Is there any possibilities the compressor can rotate the turbine shaft?

Please post your valuable reply.

It's possible that leaking valves of the centrifugal compressor could result in the centrifufal compressor rotating, but without being able to see the P&ID for the centrifugal compressor and the associated piping it's impossible to say for sure.

You really didn't tell us very much about the circumstances of when speed was being detected. For example, was it during starting of the GT? When the GT was shut down and on cooldown (ratchet or turning gear)? Was it after a unit trip from load?

Did anyone physically see the centrifugal compressor shaft spinning, or not spinning, when centrifugal compressor speed was being reported or indicated?

What alarms were being annunciated when this condition was occurring? If the centrifugal compressor speed pick-ups are connected to a Mark* turbine control system, what Diagnostic Alarms were being annunciated when this condition occurred? (Alarms, and especially Diagnostic Alarms, can be <b>very</b> helpful when troubleshooting problems like this one.)

What pumps were running when the centrifugal compressor speed was detected? Was lubricating oil being supplied to the centrifugal compressors? Was seal oil being supplied to the centrifugal compressor? Does the centrifugal compressor use bearing lift oil (sometimes called "jacking oil"), and if so, was it being supplied to the centrifugal compressor?

Was the centrifugal compressor pressurized with, we presume, natural gas, or purge gas?

I see you have checked the 'GE Mark V/Mark VI' Manufacturer Categories. Has the speed pick-up gap been checked recently? Have you checked the speed pick-ups to make sure they are all firmly being held in place at the proper gap? Has something been done to the speed pick-up wiring recently, such as during a centrifugal compressor maintenance or repair outage was the speed pick-up wiring disturbed or replaced?

You didn't say it was the Mark VI or the Mark VIe reporting the centrifugal compressor speed, but the Mark VI and the Mark VIe have very sensitive speed pick-up input circuits, and they have speed pick-up input configurations that can make them less (or more) sensitive. Has anyone changed the centrifugal compressor speed pick-up configuration settings recently?

Have you checked the centrifugal speed pick-up wiring to be sure it is properly terminated? The wiring (for passive (un-powered) speed pick-ups should be using twisted, shielded pair wiring with a shield drain wire. The shield drain wire should ONLY be terminated at one end, and by convention that is typically done at the control system end of the circuit. For active (powered) speed pick-up wiring the wiring should most likely be three-wire, twisted, shielded wiring, also with a shield drain wire, and the shield drain wire should be also only be terminated at one end (again, usually the control system end). This presumes the interconnecting wiring between the control system and each speed pick-ups is a single wire/cable; but multiple lengths of wire can also be used if the shield drain wire is properly terminated along the lengths of wires/cables. (This topic (drain wire termination) has been covered many times before on, and can be found using the 'Search' feature of It is strongly recommended you use the 'Search' Help display the first few times you use's 'Search' engine as the syntax (formatting) of search terms is probably not like your preferred World Wide Web search engine, though's 'Search' is just as fast and powerful.)

Lastly, if the speed pick-up wiring/cabling is not run in conduits or cable trays or cable trenches which are suitably separated from high-voltage or high current wires the speed pick-up circuits, because of the sensitivity, can erroneously report speed when there is none (when the shaft is NOT actually rotating). Is it possible someone ran some new wires for high-voltage and/or high current wiring in the wrong conduit/cable tray/cable trench that is causing "interference" on the centrifugal compressor speed pick-up wiring/cabling?

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You don't say anything about what type of gas turbine is driving the compressor. Is it a GE design or some other design? is it single shaft or 2 shaft? Is it heavy duty or aircraft derivative? What is the rpm it is being rotated at? Do you know for certain that it is reverse rotation and not forward rotation?

I suspect it is a 2-shaft design just because I have a hard time believing you have sufficient reverse gas flow through the load compressor to create enough torque to reverse rotate a single shaft heavy duty gas turbine.

Thrust bearing damage would be one of the more likely ill effects of reverse rotation.
The machine model: aeroderivative GT PGT25+G4 (dual shaft) GE turbine +gearbox +BCL806 compressor

>>after 2 hours of plant shutdown, the unit restated during that time i faced the problem<<

i faced the problem during startup (near to crank speed). The Gas generator speed value 1700rpm (the crank speed is 2100 rpm) so at that gg 1700 rpm the POWER turbine speed value makes 5sec spikes around 30rpm (this makes the fail start). Also I found the vibration on power turbine side, but not found in LOAD GEAR BOX or COMPRESSOR.

Please tell me any possibilities have the load compressor can rotate the power turbine shaft? if can please explain me how?
I've seen this many times on Frame 3 Twin Shaft machines driving Gas Compressors. This is usually caused by Gas Compressor gas valve sequencing (Suction, Discharge, Re-cycle, etc.). This will spin the LP Gas Turbine rotor for short or long periods of time. It could be damaging particularly if in a NO Lube Oil scenario.