*PMI Revision 00 *Turbine Lub Oil System

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*PMI Revision 00 *Presentation outlinePurpose of lubrication system.Components of lubrication system.Lub Oil circuitSpecification of oil

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*PMI Revision 00 *Importance of the lubrication systemTo reduce the wear and tear of the rotating elements.

To maintain the temperature of the bearings.

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Essentially oil is required by the bearings in order to provide continuous oil wedge on which the shaft revolves. This requires only a small quantity of oil. However shaft conductivity, surface friction and turbulence set up in the oil produce a considerable amount of heat and in order to keep the bearing temperature constant at the desired level, a further quantity of oil is required to remove the heat. Most of the oil is supplied to bearings performs the latter function.

Oil is supplied to the bearings at a pressure from 5 to 25lb/in2 (0.35 to 1.75 kg/cm2) gauge. This pressure is required to ensure that the pressure in the upper part of the bearing does not fall below atmospheric in which case discontinuities in the oil film would form. On the other hand if the oil pressure are too high the oil will be sprayed out from the bearings at a high velocity and will become finely atomized, in this condition the oil may easily escape from the bearing housing.

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HYDRODYNAMIC LUBRICATION Turbine bearings are hydro dynamically Lubricated. For this to happen following things are important1. Viscosity of oil which is directly related to the oil Temperature.2. Rotation/speed of the Rotor.3. Desired Clearances/Converging Wedge in the Bearings. (convergence should be in the direction of rotation) In fact the Pressure of the Lube oil is mainly just to ensure that oil reaches the Bearing. However it is also very important and requires to be maintained as per design.

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HYDRODYNAMIC FILM LUBRICATIONThe distinguishing characteristic of this form of lubrication is the creation of aHigh pressure wedge of oil, in the relatively large spaces between the bearing and the journal faces.

The bearing oil is supplied at a pressure of about 10-20psi (1.4 to 1.7 ksc), and the drag, coupled with the journal speed, creates a pressure in the oil wedge such that the journal begins to float on the oil. The heat generated at the bearing in this case is almost all due to shear between oil films. But even so the total power loss at the bearings of a 500MW set is about 5MW or 1%.

Heavily loaded low speed bearings require a heavy oil (High viscosity). But a lighter oil is recommended for the high speed bearings of turbo generators which depend on hydrodynamic film lubrication. The low viscosity reduces the drag andthe consequent power loss.

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The high surface speed of the turbine bearings generates high temperatures in the lubricating oil film, due to high rate of shear. Thus an oil with a comparatively low viscosity is chosen for turbine oils to keep the local temperatures below a level where high rate of oxidation would occur. On the other hand, an oil with a very low viscosity would result in discontinuities in the bearing oil films at the high bearing operating temperatures and pressures. The viscosity of the oil is normally chosen as a compromise between these conflicting requirements.

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LUBRICATIONAs rotor rotates at low speed ,initially there is no film lubrication but as its speed increases there is conversion of boundary layer lubrication into Film lubrication. From zero speed to appx. 540 RPM there is no continuos film between rotor and bearings and there is chance of rubbing between rotor and Bearing. Therefore JOP is used to prevent the contact between rotor and bearings.At Above 540 RPM the JOP can be Switched off, as film lubrication comes into picture.

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*PMI Revision 00 *Purpose of Turbine oil systemLubrication of turbine.Cooling of bearingsSealing medium in Hydrogen cooling systemTurbine barring gear operation.Working fluid in Governing system

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*PMI Revision 00 *Lubrication system components Main oil Pump.Auxiliary oil pumpEmergency oil pumpJack oil pumpMain Oil Tank

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*PMI Revision 00 *Oil coolersOil FiltersOil InjectorsCentrifugeVapour ExtractorsLubrication system components

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*PMI Revision 00 *InjectorLubrication Oil CircuitIPTLPTHPTGenMOPJOPOil coolerFilterAOPEOPMOTVap. Ext

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*PMI Revision 00 *Emergency operation of Lub. Oil System:In case of AC failure ( Black out ).

EOP will start Extend the DG supply to the emergency MCCStart AOP Start JOP.Rotate turbine with Barring gear.

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*PMI Revision 00 *Specifications of Oil: Specific Gravity 0.852 @ 50 0C Kinematic Viscosity28 csFlash point201 0C (Min)Pour Point - 6.6 0C (Max)Mechanical Impurities Nil

The recommended turbine oil Servo prime-46 of IOC.

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*PMI Revision 00 *MAIN OIL PUMP(MOP)LOCATION: This pump is mounted in the front bearing pedestal. It is coupled with turbine rotor through a gear coupling. Oil suction from MOT Through two number of injectors connected in series.Takes over when turbine speed > 2800 rpm. Supplies oil for turbine bearing lubrication as well as for the turbine governing system. .

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*PMI Revision 00 *MOP

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*PMI Revision 00 *AUXILIARY OIL PUMPS(AOPS)Two in number, AC motor drivenVertical one stage rotory pump with radial impeller & spiral casing.Supplies oil during turbo-set starting and stopping when the turbine is running at speed lower than 2800 rpm supplies oil to governing system as well as to the lubrication system.It also serves as standby to main centrifugal oil pump.Submerged pump body

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*PMI Revision 00 *EMERGENCY OIL PUMP(EOP)This is a centrifugal pump, driven by D.C. electric motor. VerticalCentrifugal submergedThis automatically cuts in when ever there is failure of A.C. supply at power station and or the lub oil pressure falls below a certain value. This pump can meet the lubrication system requirement under the conditions mentioned above.

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*PMI Revision 00 *JACKING OIL PUMPS(JOPS)JOP1 & JOP2Both pumps are AC driven but in some of the plants one of the JOP is DC driven also.To lift the rotor assembly during TG start up and shut down.Suction from MOT.delivers a pressure of 120kg/cm2 for lifting of rotor.

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*PMI Revision 00 *OIL COOLERSTo cool the lubricating oil

Consists of tube nest, inner & outer shell & water boxes

The cooling medium for these coolers is circulating water.

The pressure of the cooling water is kept lower than that of oil to avoid its mixing with oil in the event of tube rupture.

OIL TEMP. CONTROLLER for maintaining the lub oil temp at rated value by controlling the flow through the coolers.

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The efficiency of a centrifugal pump may be of the order of 55% and the remaining 45% of the pump input energy generates heat in the oil. The oil also absorbs a large amount of heat from bearing friction and shaft conduction. To remove this heat the oil is passed through coolers which reduce the temperature to that required for the bearings.

The oil and water passes are arranged in counter flow. This arrangement has thermodynamic advantages and also reduces the amount of sludge precipitated in the cooler, as the hot oil entering the cooler does not strike the coldest part of the cooler tubes.

Coolers are usually mounted vertically for easy removal of the tube nest and water passing upwards through the tubes ensures complete flooding at all times.

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The temperature of the oil must be kept within limits.

If the oil temperature, entering the bearing is too low, inefficient bearing lubrication will occur due to the high viscosity of the oil.

If the oil temperature on leaving the bearing is too high, this will lead to deterioration of the oil due to high rates of oxidation.

The temperature of the oil leaving bearing is limited to 160 F (710C) so that the Maximum temperature within the bearing is not more than 165 F ( 740C). There is a tendency, however, for these figures for rise on modern machines.

The temperature of the oil entering the bearing is about 100-110 F(37-43 0C) and the required leaving temperature is achieved by adjusting the supply of oil to each bearing.

To allow adequate adjustment, generous piping diameters are used and a removable orifice plate is often inserted in series with the control valve.

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*PMI Revision 00 *VAPOUR EXTRACTION SYSTEM

Two Vapour Extractor fansExhaust fansMaintains -ve pressure inside MOTRemoves oil fumes from the MOT.

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*PMI Revision 00 *OIL Filter

Basket type filter inside the oil tankFor thrust bearingDuplex filterFilter changeover required after choking.

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Oxidation of turbine oils usually leads to the formation of sludge which is deposited in various parts of the lubrication system, particularly in the areas of low temperature and points of low turbulence.

Water is the most important contaminant of oil, and may enter the lubricating system from leaking shaft glands, or from the condensation of humid air in reservoirs, bearing pedestals, or drain lines.

Water in oil may cause dust or scale formation in the lubricating system. The corrosion products may score the bearings or cause malfunctioning of the governing system and they also act as catalyst increasing the oxidation rate of oil.

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*PMI Revision 00 *Main Oil CentrifugeRequired for removing moisture from the turbine oil.

A portion of oil is continuously circulated through the centrifuge to remove the moisture from the oil.

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Centrifuge unit*PMI Revision 00 *

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*PMI Revision 00 *THANK YOU

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