Lubricating System on Turbine

Lubricant in this turbine is not arbitrary to be underestimated. There is a lot of damage to the turbine caused by failure to lubricate the turbine. It can even be fatal if we let it or we don’t care about it. Damage that can arise is such as bending turbine shaft, bearing damage, turbine casing damage, alternator damage. All of this starts from abnormal conditions in the lubrication system. This lubrication system applies from before the start of the turbine until after the stop of the turbine.

Turbine repair costs are generally very expensive, therefore excellent operation and good maintenance will be able to make the turbine have a long lifetime and low cost.

In large capacity turbines, the weight of the rotor is also large, so that at rest the rotor will remove the lubricant layer from the surface of the shaft and bearings. Under these circumstances the bearing or shaft will be damaged when rotated. To avoid damage due to the lack of lubrication between the shaft and bearing, a high pressure lubrication system is used to lift the rotor. As well as cooling the turbine unit.

This oil distribution 2 system uses a pump:

a. Main Oil Pump, Functions to distribute oil during turbine operation and the pump is driven by the turbine through a couple to the gearbox.

b. Auxiliary Oil Pump, functions to distribute oil before the turbine operates until the oil distribution system is taken over by the Main Oli Pump. The auxiliary oil pump will stop when the main oil pump is running. This pump is useful for distributing oil before the turbine operates and when the turbine has stopped. To keep oil circulation running for the cooling process and turbine shaft coating.

In turbine operations, or turbine oiling systems, we are familiar with the term Hydrodynamic Lubrication.

What is Hydrodynamic Lubrication..?

Fluid film or film coating or hydrodynamic lubrication is the term given when the rotating shaft of a bearing is supported by a layer or wedge of oil so that the shaft does not come into contact with the bearing material.

Basic Principle..?

The principle that allows a heavy rotor wheel to be supported by a layer of oil. This is similar to the principle that causes the car to “aquaplane” on a wet road surface. “Aquaplaning” occurs when road water builds up in front of a vehicle’s tires, and the car accelerates so that the vehicle’s load and the pumping action of the tread can push it off the road or skid. Water pressure can cause the car to lift and skid on the thin layer of water between the tires and the road. Just as a car must travel at a certain speed before aquaplaning occurs (this varies according to tire condition and road surface but is generally around 90 km/h), the axle will rotate at a certain speed before hydrodynamic lubrication occurs.

The operation of hydrodynamic lubrication in journal bearings is illustrated below. Before rotation begins, the shaft rests on the bearing surface. When rotation begins, the shaft moves up the bore until equilibrium conditions are reached when the shaft is supported on the grease wedge. The moving surfaces are then separated by the resulting pressure within the film fluid. Bearing bearings are designed in such a way that under normal operating conditions the resulting fluid pressure continuously supports the load without any contact between the bearing surfaces. This operating condition is known as “thick layer lubrication” and results in very low operating friction and very low bearing loads.

Figure 2. Hydrodynamic Shaft Turbine

The rotating shaft pulls a wedge of oil underneath which develops a pressure large enough to support the shaft and eliminate contact friction between the shaft and the bearing.

The viscosity of the lubricant is an important parameter. The higher the viscosity, the higher the friction between the oil and the shaft, but the thicker the hydrodynamic film. However friction generates heat, which will reduce viscosity, film thickness and can cause metal-to-metal contact. The use of oil with a low initial viscosity will also reduce the thickness of the oil film. We must be very careful because the distance between the two surfaces is greater than the largest surface defect. The distance between the two surfaces decreases with a higher load on the bearing, less viscous fluid, and lower speed. Hydrodynamic lubrication is an excellent method of lubrication because it allows to achieve a coefficient of friction as low as 0.001 (m = 0.001), and no wear between moving parts. However, because lubricants are heated by friction and because viscosity is temperature dependent, additives are used to reduce the temperature dependence of viscosity. The oil is of course cooled before being pumped back through the engine.

From the explanation above, we can take several important points:

• The oil should not be too cold or too hot. Because the viscosity is too high or too low is not good for  bearings.

• The selection of oil must be appropriate • The quality of the oil must be good (we need to periodically check the condition of the oil. Minimum water content and visual condition.

• Prior to loading, it must be ensured that a layer of film has been formed. How to? Make sure the oil pressure is up to standard, the heating for the turbine is sufficient (follow the proper start-up process).