TURBINE AUXILIARIES (OIL SYSTEM -LUBE ) PART-II ABC OF THERMAL POWER PLANT

PART-II

OIL SUPPLY DATA FOR A TYPICAL 500MW SET MANUFACTURED BY 

BHEL

MAIN OIL TANK, RATED CAPACITY:                       25/40             Cu . M

Ist OIL FILLING (ESTIMATED):                                   47.5                Cu . M

FLUSHING OIL QUANTITY (ESTIMATED):               28.5              Cu . M

OIL TEMP. AT COOLER OUTLET,                               38 TO 45 DEG C.

TEMP. RISE OF OIL IN BEARINGS                              20 TO 25 DEG C

OIL PUMPS

M.O. PUMP     A.O. PUMP       E.O. PUMP                         J.O.PUMP

      1                      2                          1                                  AC : 2             DC : 1

                                        

                                             CAPACITY (RATED)

      

    75                     89.25                     30                                    1.53              dm3/s

                                               

                                   DISCHARGE PRESSURE (GAUGE)

       

    8.6                     6.2                        2.3                                   178                 BAR

                                                           

                                                       SPEED

    50                   24.75                       24.3                                49.42                         /s

A Few erection points need to be remembered during erection of Lube line of turbine

1. Lube system includes jacking oil line. Jacking oil is used to lift rotor from bearing 

during starting .

2. As these lines requires lot of small items including fastners , o-ring , gasket, small 

bore pipes , prefabricated pipes, valves ,supports  etc a systematic material 

management is required to reduce the time cycle. No pipes to be kept open at the end. 

All pipes to be cleaned by compressed air before erection.

3. To start the work oil canal and oil room front availability is must.

4. All the pipelines joints small bore / large diameter should be tig welded in root.

5. Temporary pipes required for oil flushing to be made during erection itself so that 

last minute fabrication is not necessary.

6. Match up, weld and examine the prefabricated connecting pieces of the discharge 

and suction nozzles prior to the final erection of the first bearing pedestal.

7. Other matching and welding work to be done when the bearing pedestal is full 

assembled.

8. The direction of flow of the oil temperature control valve should be ensured as 

indicated by markings on the valve itself.

Jacking Oil Lines

9. Once the line has been welded to the bearing pedestal, fit a protection plate to 

protect the line in this area.

10. Ensure that oil vapor extraction lines are laid with a gradient descending constancy 

towards the main oil tank without low points. A drain loop at the lower end of this line 

upstream from the blowers return drains to the oil tank.

11. To avoid fire hazards, do not route oil lines near lines or components at high 

temperature.

Oil tank with pump motor on the top.

Typcal 500MW lub oil scheme is given above ( BHEL make sets) 

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TURBINE AUXILIARIES (OIL SYSTEM -LUBE ) PART-I ABC OF THERMAL POWER PLANT

In continution of my last dispatch regarding Generator Gas system two

photographs of the system is attached.

TURBINE  LUBRICATION OIL SYSTEM 

 Turbine lubrication system is the most important auxiliary system in TG Package. As 

I discussed seal oil system of Generator , lubrication system of Boiler auxiliaries like 

FANS ( ID ,FD and PA) ,Mills and Airheaters. Therefore it is felt prudent to discuss 

the oil system of Turbine .

The Turbine Lube Oil System functions to provide storage, cooling, and continuous 

purification of the lubricating oil required for the main turbine and generator.

Turbine lube oil system contains following equipments and piping.

- A Turbine oil tank

- 2 Nos AC motor driven pumps for lubrication system

- One main oil pump ( coupled with main turbine )

- One Jacking oil pump ( 100%)

- One DC lube oil pump ( 100%)

- Two oil coolers ( 2x100%) with cooling water connection and change over valves.

- Duplex  oil filter

- Instrumentation Racks and Instruments local and remote.

- Turbine oil purifier portable having capability purification of 20% of tank volume.

- A central oil purification system.

- Piping portion of them pre- fabricated and rest are site routed.

-Two full capacity oil vapour extractor.

Piping shall be routed in a manner to avoid crossing or being directly above any 

steam lines and to allow gravity drainage where possible. The high-pressure supply 

piping shall be guarded by low-pressure return piping. Coolers and pumps shall be 

physically located in the oil reservoir. The supply and return piping shall be sloped to 

avoid air pockets and to allow proper drainage. Total erection jobs takes around 04 to

05 months depends up on the readiness of the Oil canal , Positioning of Pedestals (brg)

oil room including oil cooler foundations ,tank foundations other small foundation 

etc. Clean pipes and enviornment will help to reduce the oil flushing time . Therefore 

a system of preservation ,cleaning by compressed air is must during erection. All 

welding on pipelines to be completed otherwise it will be difficult to do it afterwards

due to potential fire hazards.

Oil tank with instruments are shown in the picture. Pumps are installed on the tank.

continued
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GENERATOR AUXILIARIES (GAS SYSTEM ) PART-III ABC OF THERMAL POWER PLANT

GAS SYSTEM: Generator is cooled by introducing H2 gas as coolant. Heated H2 gas is cooled on Hydrogen cooler attached with generator. Primary water cooler and Hydrogen Cooler is cooled by DM water supply from the system either from CEP discharge or closed loop ACW system.

Use of H2 gas needs special attention because if it mix with air it may explode. Therefore safety precaution is paramount in case of Gas system. No half measure to be taken during erection and commissioning of the system. Only experienced personal should handle the system with safety precaution. I will outline the gas system required for the generator in brief.

The gas system consists of the following components:

- CO2 cylinders

- H2 cylinders

- N2 cylinders

- Gas dryer

-Gas valve manifold

Hydrogen Gas with Purity of 99.7 % minimum is charged from the cylinders to the manifold . The cylinder pressure is much higher than the required pressure . Therefore two parallel connected pressure reducing valves are used to take care of expansion.

As a precaution against explosive mixtures, air must never be directly replaced with hydrogen during generator filling not the hydrogen replaced directly with air during the emptying procedure. In both cases, the generator must be scavenged or purged with an inert gas, carbon dioxide (CO2) being used for this purpose.

CO2 is also supplied in liquid from and in compressed condition. During CO2 filling  temp control is necessary and is provided in the rack to save from excessive cooling.

To remove the CO2 from the generator,(during commissioning or on shut down) a compressed air supply with compressed air filter is connected to the general air system of the power plant. Under all operating conditions, except for CO2 purging, the compressed air hose between the filter and the generator pipe system should be physically disconnected. This is to avoid any contact with Hydrogen and air.

A gas valve rack is furnished with a mini diagram on the face of the panel to show the system . The valves used in the gas system have rubber/metal sealed valve seats to ensure gas tightness.

For measurement of Pressure transmitters are used. Also analyser , purity meter is also used in the instrument panel.

A small amount of the hydrogen circulating in the generator for cooling is passed through a gas drier. The gas inlet and gas outlet pipes of the gas dryer are connected at points of the generator with different static heads(differential fan pressure), so that the gas is forced through the dryer by the differential pressure only. Gas drier is electrically operated with temperature control.

A typical PID diagram is attached (BHEL make) below.

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GENERATOR AUXILIARIES (PRIMARY WATER SYSTEM ) PART-II ABC OF THERMAL POWER PLANT

We are breifly discussing the important auxiliary system of Generator . In part-i

we discussed about the seal oil system of generator. Now i will describe briefly

about primary water system used in power house of 500 MW above rating sets.

The treated water used for cooling the stator winding, phase connectors and 

bushings is referred to as primary water in order to distinguish it from the 

secondary coolant (raw water, or condensate). The primary water is circulated in 

a closed system and dissipates the absorbed heat to the secondary cooling water

The pump is supplied with hot primary water from the primary water tank, and delivers the water to the generator via the coolers. 

Primary water system comes as a skid only pipelines and cabling connections are to be made after erection. Skid erection gives front for piping erection and this job can be done  independently . However the total piping job including impulse

piping of instruments to be done by SS material. Stator purity is challenge to erection and commissioning engineer therefore system should be leakproof . O2

measured in the stator water in p.p.b. ( parts per billion).

The skid contains 2x100% pumps , 2x100% coolers , filters , primary water tanks ,necessary valves and insrtumentations. A typical PID is given below.

Flow path I of primary water is used for cooling the stator winding.

This flow path routes the water to the manifold at the exciter end and from there to the stator bars via insulating hoses. Each stator bar is connected to the manifold by a separate hose. The cooling water flows through hollow conductors towards the turbine end of the generator. After exiting the stator bars, the water flows through insulating hoses to a water manifold from where it is rerouted to the primary water tank.

The other flow path is for cooling the phase connector and bushings.

The bushings and phase connectors are made of thick-walled copper tubes carrying the cooling water. The 6 bushings and the phase connectors, which are arranged in circular fashion around the stator-end winding, are interconnected in such a manner that 3 parallel flow paths are established. The cooling water is admitted from outside the generator through 3 bushings and exits through the other 3 bushings.

The secondary water flow through the primary water cooler is automatically controlled to ensure that the generator temperature is maintained at a constant level under different load conditions. 

continued to part-iii

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