GENERATOR AUXILIARIES (SEAL OIL SYSTEM ) PART-I ABC OF THERMAL POWER PLANT

Till  last dispatch I have outlined the installation of turbine and generator of thermal power plant briefly with the help of photos. I have also discussed what are pitfalls during erection . From now onwards I will discuss about few important systems /processes required for Turbine and Generator so that readers can have an idea of the total system of a power plant. I will first discuss about the Generator System.

 Shaft seals supplied with pressurized seal oil are provided to prevent hydrogen losses at the shaft and  the ingress of air into the hydrogen-cooled generator. All generators having rating more than 500 MW stator winding is cooled by water and rotor winding is cooled by Hydrogen. Stator water and Hydrogen is again cooled by water as secondary cooling through stator water cooler and hydrogen cooler. As long as the seal oil pressure in the annular gap is more than the gas pressure in the generator, no hydrogen will escape from the generator housing. During normal operation, the air side seal oil pump (AC) draws the seal oil from the seal oil storage tank and feeds it to the shaft seals via coolers and filters. The seal oil supplied to the shaft seals which drains towards the air side through the annular gaps between the shaft and seal rings is returned to the seal oil storage tank. For the air side seal oil circuit, three seal oil pumps are provided with one of the three pumps always in operation. In the event of a failure of the pump in service due to a mechanical or electrical failure, the second pump automatically takes over. If both pumps fail, the seal oil supply is taken over by the stand-by pump without any interruption.

During normal operation, the hydrogen side pump draws the seal oil from the seal oil storage tank 

and feeds it to the shaft seal via coolers and filters. The seal oil supplied to the shaft seals which 

drains towards the hydrogen side through the annular gaps between the shaft and the seal rings is first collected in the generator pre-chambers and then returned to the seal oil tank.

Oil pressures which exceed the generator gas pressure are required to ensure proper sealing of the generator. With the seal oil pumps in operation, the seal oil pressure is controlled by differential pressure valves. The first valve controls the seal oil pressure after two equal-priority ac air side seal oil pumps. The pressure after the stand-by seal oil pump is separately controlled by the second valve. Depending on the valve setting and the impulse oil pressure prevailing (seal oil pressure and hydrogen casing pressure), a larger or smaller amount of oil is returned to the suction pipe so that the required seal oil pressures is established at the shaft seals . A typical seal oil circuit is given below. Now seal oil system is coming as a skid item where every item is connected ,pre-wired and instrumentation completed. Only job is left to connect the lines from different places with proper slope. However only small disadvantage is there i.e. the size of the skid is fairly big because of cooler and tank fitted on it. If proper co-ordination is not done there will be problem on shifting the same to foundation in one piece. One must keep in mind pre-plan its path before hand.

typical seal oil system P&ID diagram of BHEL supplied 5000MW set.
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ERECTION SEQUENCE AND PLAN FOR GENERATOR PART-III ( ROTOR INSERTION) CONCLUDING PART. ABC OF THERMAL POWER PLANT.

 

ROTOR INSERTION PROCESS STARTED.

PLEASE NOTE THE ARRANGEMENTS MADE ON THE ROTOR FOR FIXING LIFTING CEILING FROM EOT CRANE .

PLEASE SEE THE CEILING POSITION WHEN APPROX 50 %ROTOR INSERTED. ALSO LOOK
OUT FOR THE MAX PULLER FITTED BOTH SIDE OF STATOR TO FACILITATE ROTOR INSERTION.

INSERTION PROCESS COMPLETED

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ERECTION SEQUENCE AND PLAN FOR GENERATOR PART-II ABC OF THERMAL POWER PLANT.

Some of the checks are to be carried out before rotor threading is  given below

All electrical tests (dc resistance, IR value and impedance) are carried out on rotor.

Stator is thoroughly cleaned and free from foreign elements like dust, oil/water, spanners, screwdrivers etc.

All electrical tests (dc resistance, IR value) are carried out on stator.

Check healthiness of thermocouple/RTDs of stator core /winding.

Check locking of bolts of clamping plate of stator overhang. Check busbar supports for tightness .

Tightness of compressor blades for axial movement is checked

Check and ensure for locking of all balancing weights to be checked visually / hand feel.

Measure and record male spigot/journal dimensions of rotor on both ends.

Vacuum cleaning of all ventilating holes is carried out and transportation packing & blower protection cover on rotor is removed.

Check through-ness of radial ventilating holes of rotor winding 

Stator is getting  ready for rotor insertion.  please notice the arrangement of maxpuller both sides  and the

piece of rubber solid  laid inside the stator.

Zigs and fixtures are moved and are getting placed in position.

Rotor is brought near to stator for insertion. Please look out for zigs and fixtures

Continued to PART_IIIIP.S

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ERECTION SEQUENCE AND PLAN FOR GENERATOR PART-I ABC OF THERMAL POWER PLANT.

-Foundation Checks  to be carried out. Generally this was done with turbine foundation checks.

- Installing the Foundation Beams and the Sole Plates

-Checking of  High-Voltage Bushings and the Current Transformers for  healthiness.

-Positioning of Terminal Box before generator lifting .

-Lower the Generator Frame on Supports after lifting either by EOT crane/ some other method.

-Assembling of Terminal Box, External Seal Welding, Leak Test

-Mounting of Cooling Header, External Seal Welding, Leak Test

-Lower Generator and Perform Preliminary Alignment with the help of jacks .

-Aligning the Foundation Beams with and Bolting them to the Generator

-Installation of Alignment Brackets

-Installing the Primary Water Tank on the top of the generator.

-Installing the Current Connectors

-Prepare the Bottom-Half End Shield Bearings

-Preparing of Rotor for Installation

-Installation of Rotor

-Mounting of Bottom-Half End Shield Bearing, Emplacement of the Rotor

-Lay Rotor Axial to the Generator Frame

-Installation of Air-Gap Seal

-Installation of External Current Connectors (Beginning)

-Alignment of Generator for Release for External Connections

-Measuring the Bearing Clearances

-Pre-assembling of Inner Oil Wipers

-Recording the Dimensional Data of the Seal Ring and the Seal Ring Holder

-Mounting of Compressor

-Mounting the End Shield Bearing Top Halves

-Installation of Inner Oil Wipers

-Alignment of Compressor

-Aligning the Generator and Turbine Couplings

-Grouting of Foundation Beams

-Installation of Gas Distribution System

-Mounting of H2 Cooler

-Final Inspection of the Generator Interior and Mounting the Manhole Covers

-Tensioning of Foundation Anchor Bolts

-Preparation of the Bearing and Seal Oil Systems for Flushing

-Checking Instrumentation and Commissioning Seal Oil System (Beginning)

-Filling the End Shield Bearing Seal Grooves

-Installation of H2 Shaft Seal

-Generator - Leakage Test (Air)

-Final Alignment of Generator to Turbine

-Closing of Bearing Chambers

-Handover of Customer Tools, Winding Up Assembly Site

-Preparation of Exciter Foundation

-Preassembling of the exciter base plate

-Alignment Of the Exciter Coupling to the Generator Coupling

-Grouting the exciter base plate and tensioning of the anchor bolts

-Couple the Exciter shaft and swing check

-Final assembling of the exciter

-Following interface activities to be released as inputs for other system to connect.

-Release for the Oil Line Connection to the End Shield Bearings

( 10 to 12 weeks from start)

-Release for Primary Water Line Connections

( 10 to 12 weeks from start)

-Release for Installing the Foundation Cover

( 14 to 15 weeks from start)

-Release for Cooling Water Line Connections (H2 Cooler)

(16 to 17 weeks from start)

-Release for Bus Bar Interface at the Terminal Bushings

( 21 to 22 weeks from start)

-Release for Connection of Piping to the Exciter Bearing

(24 to 25 weeks from start)

-Release for Cooling Water Line Connection to the Exciter Coolers

(28 weeks from start)

-Release for Coupling of the Steam Turbine 

(28 weeks from start)

The total work is planned for 28weeks to 30th week depending on availability

of materials , civil fronts , availability of EOT crane and other aspects of site.

Out of the above activities one activity is extremely critical considering erection 

angle i.e rotor threading to Generator stator. This require pre-planning of 

material ,manpower and T&P with utmost care.  The same will be described

in PART_II through pictures.

Please observe ceiling protection , support on pedestal etc.

GENERATOR PKG ERECTION PART-IV,( CONCLUDING) LIFTING ARRANGEMENTS OF GENERATOR - ABC OF THERMAL POWER PLANT.

Final part of generator erection with strand jack system is given below through

pictures. Process of genrator erection by strand jack or by crane will be same.

Conitinued to Part -V about erection sequence and other integral system of

Generator.

GENERATOR PKG ERECTION PART-III, LIFTING ARRANGEMENTS OF GENERATOR - ABC OF THERMAL POWER PLANT.

PART -III

In continuation to my  last blog on erection of generator by strand jack method 

part-ii more pictures now being added to make the erection procedure complete.

Continued to Part-iv 

GENERATOR PKG ERECTION PART-II, LIFTING ARRANGEMENTS OF GENERATOR - ABC OF THERMAL POWER PLANT.

PART- II

Stator lifting by EOT Cranes:-

In earlier days up to 210 /250 MW class the stator is being lifted by two EOT cranes of similar capacity  with lifting beam. EOT cranes main hooks are fitted with the lifting beam and lifting beam main hook is being utilised for lifting stator by using special sling designed for the above purpose. Stator  is placed in the service bay within the approach of EOT crane and unloaded from Trailer / wagon as the transportation method available in the power house. Earlier days a railway line runs  across the service bay. Now a day’s all the stator is coming by high capacity hydraulic Trailer.  Stator is unloaded by hydraulic jacks on temporary supports in the service bay. Fix the trunion plates (04 nos) with the body of the stator after necessary cleaning and blue matching with stator body. This has to be fixed as per the norms because sling will be placed on it. Clean the terminal box and do the blue matching with surface plate. This are the preparatory work for stator lifting. Terminal Box can be placed before stator if there is no other possibilities push it from bottom. Stator is lifted by tandem operation with lifting beam from any of one the crane. This arrangements to be tested before put in actual use. Necessary adjustment to be carried at that time, to avoid any jerk during the operation.

Stator lifting by Portal crane or by strand jack method.:-

Once we are start erecting 500 MW /600 MW /660 MW /800 MW generators the weight of the stator

increases considerable therefore alternative lifting arrangements are thought of . Some of the

utilities  think about the lifting irrespective of loading TG  bay . Otherwise total TG bay need to designed taking stator weight as one of the factor.  Portal crane and strand jack method came as solution. It has been seen availability of Portal is a problem. In my service life we have noticed  that once we need to erect 09 numbers of stator in a year and we have only two portal cranes. Portal dismantling , transportation and re –erecting is 03 to 04 months cycle depends on location of both the sites . We cannot erect all the Generators required by management and to solve this problem stand jack method of stator lifting was adopted. This type of lifting was already popular for boiler drum lifting.

Placement of stator for this type of lifting is very important. The stator need to be placed outside A row column and between transformer bay and A row column. Centre line  of  Generator from TG to be brought and marked for stator placement . No axial movement is possible when stator is placed on foundation. Foundation for jack pads and lifting structures are needed for unloading  the generator  and placed on temporary supports. All other works to be done on generator is same. Stand jack system to be erected by EOT crane and Heavy lift Crawler crane from AB bay and Outside A row. Close co –ordination is required from all quarters as that area includes the area of CW pipelines  for Condenser. Clear approaches is required for heavy duty crane and Hydra cranes.

As the main column pitch distance is less than the stator length swivel arrangement is required in strand jack system. Strand jack system is totally hydraulic and operates slowly it may take  06 to 08 hrs from start to complete the lifting and placement  operation.

Continued to Part -III for more pictorial representation.P.S If  you are looking to earn few extra money from the comfort of your home then please click on the link given below

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