How Does Gas Turbine Lubrication Work? Benefits and Protections Explained

Lubrication is a technique in which lubricant is use to reduce friction between rotating parts such as Bearing and shaft.

The lubrication system produces cooled, filtered oil for the bearing of the Gas Turbine and the Generator. The lubricating provisions for the turbine, generator, torque converter and accessory gear box are incorporated in a common lubrication system which includes a main lubrication oil pump, full size auxiliary lube oil pump driven by AC motor, an emergency lube oil pump driven by a DC .

The lube oil system supplied cooled & filtered oil for Lubrication of:

• GT & Generator’s Bearings
• Auxiliary gearbox
• Torque Converter
• Hydraulic system

Components

• Main oil pumps shaft driven
• AC driven auxiliary pump
• Dc motor driven emergency pump
• Heat Exchangers (HX-1 & 2)
• Lube oil filter (OF-1 & 2)
• Pressure regulator valve (VPR2-1)
• Lube oil tank (Capacity 12500L )
• Mist eliminator (88QV)

Note: You can download the labeled P&ID of lubrication system of Gas Turbine to see the equipment codes and for better understanding.

Auxiliary Lube Oil Pump:

The auxiliary lube pump is a centrifugal type pump driven by AC supply. It will be used in startups and shutdowns to provide lube oil for lubrication. When shaft will attain self-sustaining speed, it will be automatically cutoff.

AOP = 6.89 bar

(AC Motor)

Main Lube Pump:

The main lube pump will be used when shaft will attain self-sustaining speed which will 1800 rpm. The full load speed will be 3000rpm. It is shaft driven no AC supply as in case Auxiliary lube Oil pump.  It has following pressure

MOP = 6.89bar,

(Shaft Driven) (Engage >95% speed)

Heat Exchanger

The heat exchanger system is required to dissipate the heat absorbed by the lubricating fluid and to maintain the fluid at the proper bearing header temperature. This is accomplished by circulating cooling water through the cooling tubes of the heat Exchanger as the lubricant flows over the tubes. Cooling water flow through the heat Exchanger is controlled by temperature control valve.

Temperature Regulating Valve (VTR)

Temperature regulating valve. It is a three way valve which controls the temp: of lube oil by CCW. Maintain 54 °C lube oil temperature.

Lube Oil Filter:

Filter are generally installed to separate unwanted material from product. So they are used to clean the lube Oil.

Mist Eliminator

The main function of mist eliminator is to remove the oil vapor and to maintain the negative pressure at the tank to avoid the pressurization of tank and preventing the lube oil leakage from tank. The lube comes along with the vapor is filtered and diverted back to tank and oil vapor is thrown out to the atmosphere.

Emergency lube Oil Pump

This will supply lube oil in case there will no AC supply so DC supply will be given in case blackout.

EOP = 1.37 bar,

(DC Motor Driven)

Lubricating oil conditioning includes:

• Oil tank warming up to keep acceptable oil viscosity while the unit is at standstill
• Oil flow cooling down to evacuate heat from the bearings
• Oil flow filtering
• Oil Header Pressure regulating at constant pressure
• Oil mist elimination

Protections & Alarms

• Lube Oil pressure at generator bearing (63QT-2A) 0.55 bar trip value 2/3 logic.
• Lube Oil header temperature high-high is LT-TH-1,2,3 is 82.2 degree C when unit is running at operating speed greater than or equal to 99.5 %.
• Lube Oil header pressure low 2.8 bar.
• Emergency lube oil normal operating pressure 1.37 bar

Bonus: Download API of Gas turbine for greater and deep understanding free.