While a GT is running at part load, can the EOP support the lubrication system continuously if the MOP and AOP fail simultaneously for some reason? Please reply.

Regards,
calvein.

 

You didn't list the manufacturer of the GT. For GE design gas turbines, the emergency lube oil pump is sized to protect the bearings during coast-down and cooldown following a trip. This is why the setting of the pressure switch that turns on the EOP (63QL) is set lower that the pressure switches that trip the turbine (63QT-1,2,3) on low lube oil pressure.

 

In that case we have to see two things, one is Emergency oil pump (EOP) is running on Direct current. so you have to have a good DC source that will give continuous DC supply to the pump during the plant on part load. second is, normally EOP's head is less than the MOP and AOP head(flow normally the same). Even though plant is on part load, EOP's oil supply to the bearings with less head is not sufficient to remove the heat generated in the bearings. So EOP oil flow with less head is sufficient to remove the heat from the bearing during coasting down, when m/c is on no load.

 

For a Frame 9E you will trip. The low oil pressure trips switches 63QT have set/reset setpoints of 8/9 psi. The DC lube oil pump will only provided 5-6psi when running. ie It is less than the trip point. So regardless of whether the bearing sustain the required lubrication the software will take you out.

This is a very unlikely case. If your MOP fails your AC pump should start and the turbine continue to run. If your grid MCC supply fails you will come down on your EOP however the MOP will still contribute oil flow until a very low shaft speed.

If your MOP and AOP have both failed you are on your last chance with no additional backup. The turbine should not be running in this state. Further failure of the EOP will result in mechanical damage.

Our units perform a EOP test during the purge crank. The EOP current has to exceeds a certain amps and discharge pressure higher than a certain value for the start sequence to continue.

 

I have never seen a system on any industrial turbine which has a a Main and & Aux. LO pump where the Emergency LO pump is anything but a rundown/cooldown pump. The chances of losing both the Mechanical and AC LO pumps at the same time are fairly small and the capacity of battery bank required for a continuous DC Emergency LO pump would be prohibitive. For these reasons, Emergency LO pumps are usually only for shutdown/cooldown. On GE industrials, the battery bank is usually sized to give you 18-24 Hours operation which is enough cooldown time to get the machine cooled down and off Lube Oil. Most modern sites will usually have some kind of Black Start or Emergency generator facility as a complete station blackout would be one of the most problem causes of a shutdown without AC power therefore the use of the Emergency LO pump.