Precautions To Be Taken In Turbine Bearing Lubrication System

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The turbine unit’s oil system is one of the most important integral parts. It influences machine reliability and maintenance-free operation. The primary function of the turbine oil system is fluid friction in turbine bearings, generators, feed pumps, and gearboxes.

A Functioning Oil System Should Have Below Working Principles

Continuous supply of oil at all operating modes, which ensures:

  • Preventing wear on friction surfaces
  • Reduction of friction power losses
  • Heat is removed from the turbine’s hot parts by friction.

Maintaining the oil at the right temperature in the system.

Cleanse the oil to prevent contamination.

The lubricating oils system must also have safety, reliability, and ease of maintenance.

During the operation of the turbine unit, it is essential to monitor the oil temperature and pressure. Overheating the bearing can cause wear to the bearing’s working parts and changes in the lubricant’s properties. The physicochemical properties of the lube oils, such as density and viscosity, control how good the lubricating oil is. Leakages must be dealt with immediately, and oil should be replenished promptly. These factors will significantly extend the life expectancy of the steam turbine.

Effects of Abnormal Lubricating Oil Temperature

This section describes the adverse consequences/operating concerns caused by this temperature outside the normal operating range.

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When bearings are supplied with lubricating oil that is too cool, the following adverse consequences/operating concerns result:

  • Increased chance of turbine generator vibrations due to oil whip or oil swirl.
    This is a simplified explanation of the phenomenon. Oil viscosity rises with decreasing temperatures. Oil in bearings tends to stick to the shaft surface and be pulled around the bearing. Oil temperature drops too much, which causes oil to be driven around bearings. The oil wedge loses stability and causes high vibrations in turbine generator rotors.
  • Increased chance of overheating.
    It is not surprising that cool oil can cause bearing overheating. This can be explained easily. Oil viscosity decreases with temperature. This causes more excellent resistance to flow through bearing oil supply pipes. This reduces the oil flow rate at most stations. The centrifugal variety’s main, auxiliary, and emergency oil pumps are used. (Remember that the capacity of centrifugal pumps is sensitive to the system head. Bearing overheating may result from inadequate oil flow.
  • Forced protective measures can cause production losses.
    Specific protective measures prevent damage from oil whip and bearing overheating. The turbine generator might need to be unloaded and tripped. These actions are necessary for Equipment Protection, but they can lead to production loss, for which poor oil temperature control could be responsible.

If the bearing inlet oil gets too hot, it can lead to the following negative consequences and operational concerns:

Risk of bearing injury increases due to:

  • Overheating as the hot oil can’t keep the bearing metal temperature below a safe level.
  • Contact between the shaft, bearing lining and metal-to-metal.
  • Vibration levels are increased.

These two effects result from reduced oil viscosity due to higher temperatures, which causes a thinner oil wedge inside the bearing. The reduced thickness of lubricating oil increases the chance of the oil wedge rubbing against the shaft and bearing lining. It reduces vibration dampening of motor rotors, which results in higher vibration levels. The bearing oil wedge is the primary source of vibration dampening. This works in the same manner as hydraulic shock absorbers to dampen the vibrations of the car suspension.

Forced protective measures can cause loss of production:

High bearing metal temperature and vibration can cause turbine unloading or trip and loss of production. This can be caused by inadequate oil temperature control.

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Turbine Lubricating Oil Impurities, Sources And Adverse Consequences:

Turbine lubricating oils contain four main impurities: water, oxidation product, gases, and abrasive particle.

Water:

Sources:

  1. Absorption by atmospheric moisture
  2. Leakage of the turbine gland seal
  3. Leakage in the oil cooler

Absorption by atmospheric moisture:

During the turbine operations, atmospheric air always containing water vapor enters the oil system through the bearing oil seals.
Leakage occurs because:

  • Too high shaft surface velocity to allow contact between shaft and seal. This leaves a leak path open.
  • Possible leak routes include missing or poorly fitted gaskets in drain lines and lube oil tank covers.
  • The oil tank can be inspected during turbine shutdown. This creates a large contact zone between the oil in the tank and the humid atmosphere in the turbine hall. Condensation of moisture is encouraged because the oil in the tank may be pretty cool during the shutdown.

Leakage of the turbine gland seal:

The humidity in the air around a leaky gland seal will increase. As described above, humid air enters adjacent bearings. This is made possible by the close distance between the turbine bearings and the nearby gland seals.

Leakage in the oil cooler:

A leakage in the cooler can cause oil contamination by allowing water into the oil. This can be prevented by keeping the oil pressure higher than the cooling water pressure in most stations. These stations can still be affected. Water in-leakage may occur when the turbine is shut down and the oil pressure is low.

Operating Concerns and Adverse Consequences of Water:

  1. Oil properties that have been degraded due to:
  • Formation with Emulsions whose lubricative qualities are lower than pure oil.
  • Cleaning out special oil additives such as rust inhibitors.
  • Accelerated Oxidation of Oil and Its Additives.

Oxidation Products:

Sources of Oxidation Products in Turbine Lubricant:

Normally oxidation products are formed by complex chemical reactions between oil, air, and water. As the temperature rises, so does the rate of oxidation. Oil oxidation can also be accelerated by water and certain metals, like copper. Resins, sludge, and organic acids are the final products. When contaminated makeup oils are used, oxidation products can be added to the system.

Operating Concerns and Adverse Consequences of Oxidation:

  • Degradation by sludge or resins of oil-lubricating properties
  • Acidic solutions can accelerate the corrosion of system components.
  • Sludge accumulation in bearing oil passages, coolers, Filters, valves, etc. This can lead to many problems, such as reduced oil flow and valve sticking.
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Gases:

Sources of Gases in Turbine Lubricant:

These substances can be introduced to or produced in the lube oils system as follows:

  1. Air can enter the system via bearing oil seals and lubricant tank cover gaskets
  2. When oil flows through the generator, hydrogen seals absorb carbon dioxide and hydrogen.
  3. Oil vapor is produced by the lube oil tank, which has drain lines that are only partially filled with hot oil.

Operating Concerns and Adverse Consequences of Presence of Turbine Lubricants:

  1. A mixture of oil vapor, hydrogen, and air in the oil tank atmosphere can cause explosion and fire hazards. This could lead to equipment damage and safety hazards.
  2. Accelerated oil oxidation and system corrosion due to air and carbon dioxide.
  3. Possible oil foaming worsens the lubricating and cooling properties of the oil and may impair pump performance.

Abrasive Particles:

The following are some of the most common sources of abrasive particles found in lube oils:

  • Normal wear and corrosion can cause tiny metal particles, fibers, and rust from the gaskets. Equipment failure (e.g., failure of the main oil pump impeller can also cause larger debris.)
  • As described previously, dirt in the air is sucked into sub-atmospheric parts of the system.
  • After maintenance in dirty conditions, poor system flushing, and leftovers are also sources of abrasive particles in the turbine lubricants.

Negative Consequences of Presence of Abrasive Particles in the Lubricating Oil:

Abrasive particles in oil can have a major negative effect on the equipment. It accelerates the wear and causes failures. Large particles can scratch the shaft journals, surfaces, and generator hydrogen seals. Very fine particles can cause waviness if left unattended for a long time. Abrasive particles could cause system malfunction or even catastrophic failure.

Conclusion:

This article briefly describes the turbine Bearing Lubrication System and precautions to be taken during turbine lubrication. Many improvements are going on in this modern era on the tribology and lubrication of different applications to reduce the friction and wear and increase the application life.
If you want to add any more suitable information about the article topic, you can mail us at industrialubricants@gmail.com

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