GERB Spring Loaded DECK Inf

7/28/2019 GERB Spring Loaded DECK Inf

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SPRING SUPPORT OF TURBO GENERATOR FOUNDATIONS

2.0 Advantages of spring loaded foundation

2.1 Minimization of Mat size and construction cost:

Table foundations of turbo generators had been an almost universal practice.

Thick base mates were required as a dynamic Counter mass and in order toprevent significant settlement especially in case of poor subsoil conditions.

The vibration to the main columns is isolated by the spring elements resultinginto small size base mat, which reduces the construction cost & time.

2.2 More space below the TG for the arrangement of condensers and piping:

The same column to TG deck may also be used to support surrounding floors at

the building so that the total number of columns is reduced and the space to

accommodate more equipment is increased. (Compare the space available atDahanu units below TG with any conventional 210 MW TG halls, the differencecan be seen.)

2.3 Handling of settlement problems:

Progressive settlement can interrupt normal operation and lead to major shutdowns. Easy adjustment in the event of settlements is feasible with springsupport by inserting or removing shims in spring units.

2.4 Better load distribution due to the spring support.

2.5 Earthquake Protection:

Machine will have more stability in t he event of earthquake as compared tonormal foundation. In order to protect the plant against earthquakes and toavoid resonance, the spring units are partially combined with Visco damping.

3.0 How is the spring support system designed?

BHEL designers (in case of TG, HWR) supply the following information to GERB

1) Sizes of equipments to be supported.

2) Loads location of loads, direction of force components (in Fx, Fy, Fzdirection).

Following loads are considered while furnishing the information to GERB

1) Static load of components.

2) Rot. Elements

3) Power torque

4) Vacuum loads.


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5) Thermal elongation

6) Loads when one half of condenser is in operation.

7) Forces & moments of steam piping

8) Friction forces.

9) Maximum allowable unbalance

10) Loss of blade unbalance

11) Short circuit forces

12) Seismic loads

13) Bolts stretching & erection loads.

Based on above information GERB designs the springs & Visco dampers & decides on

their numbers at various columns.

In case of Dahanu 2 x 250 MW complete TG deck is supported on 10 columns, 5 eachside of the axis.

Types of spring supports used at Dahanu.

GERB supplier various coil sizes, number of coils & turn depending on columnloading & type of loading.

Combination of S-9 at A7A column, S-2 at B&B, S-11 & S-6 at C&C columns, S5 at

D&D columns, S-5 & S-8 at E&E Columns have been provided.


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4.0 GENERAL ARRANGEMENT OF SPRING LOADED DECKS

Items supplied by GERB:

GERB supplies the complete isolation system consisting of spring units,viscodampers, fixing materials, leveling shims and mounting equipments.

They supply the damping fluid for viscodampers.

Preparatory work before installing the spring units-

The spring system is mounted when the shuttering of RCC slab of TG deckis ready.

The top surface of individual column where these springs are mountedshould be within accuracy of 00 to 3,00 mm. If necessary these may becorrected by chipping before installations of the spring units. The leveldeviation among various columns is permitted 00 to 5, 00 mm in total

including individual column variation of 00 to 3,00 mm.

Scheduled column elevation


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The cover steel plates to close the deck opening above the spring units must be providedwith anchor bolts or similar arrangements on the upper side spaced no more than 300mm in each direction. Thickness of the plates should be at least 10 mm.

Prestressing of spring units:

The spring units are delivered to site slightly prestressed for the purpose of

transportation.The required prestressing of the springs (based on column load) is done atsite before their installation in position.

Prestressing corresponds to

a) Static deflection of springs due to operation loads.

b) An additional deflection of 5 mm to cover temporary over loading

during the machine installation.

This additional deflection of 5 mm is equalized by shims on top of the springunits, which are removed when the prestressed units are released.

(This means, that the top level of foundation is 5 mm lower and will reach finallevel after releasing spring units).

A note on additional loading on springs by providing 5 mm shims

The springs units are not only pre-compressed for Calculated load of the machinebut it is further pre-compressed to prevent the loosening of the spring during

installation of the equipment due to unforeseen additional loads. If majorvariation in calculation of load over the spring units is not expected then an

additional compression of 5.00 mm is sufficient for this purpose. These shims areremoved at the time of loosening of spring elements before final alignment of themachine. It is also not necessary to remove this complete 5.00 mm shims foreach spring unit and the same may vary form spring unit to spring unit dependingupon the variation of column level / elevation and variation in level of springcover plate etc.

The spring units are compressed in special steel frame with hydraulic jacks.

The elements are locked in this position by the side bolts into eh spring units.

(Steel frame and jack are supplied by GERB).


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Mounting of spring units:

Before the spring units are mounted, the supporting beams columns aremarked where the units are to be located, as per the drawing.

One adhesive resilient pad is placed on the surface of the supporting beamcolumns for each element. The pad has same size as the contact area ofthe element.

The prestressed spring units are placed on top of the adhesive pads with acrane. Threaded holes are provided on top of the spring units to use eye-

bolts (M-20).

(Caution: The heads of the prestressing bolts must be on the upper side!!!)

Like a sandwich a stack of adhesive pad steel shim and another adhesivepad is laid on top of the spring units, as per calculations.

(Adhesive pads are used to avoid movement of the spring units/shimsduring operation of the machine)

If the level of the upper adhesive pad is not in accordance with the drawing

the difference should be corrected by reducing or adding steel shims.Then, a plastic foil is wrapped around the spring units to give protectionagainst concrete milk or dust.

Finally, the cover steel plates are placed over the spring units. The coversteel plates will stay in position after-wards and will not be removed. It willserve the purpose of equal distribution of pressure, when jacks are used

for the leveling procedure or for the release of the spring units.

(Caution: The bottom sides of the steel plates and the bottom sides of thepedestal (deck) must be on the same level).

(Figures given at the end)

Condition of the springs when machine is assembled

Springs remain in locked prestressed condition when machine is

assembled.During the installation of the machine the deck may settle 1-1.5 mm

without prestressing bolts of the spring units becoming loose.

(The reason is a possible plastic compression of the adhesive resilient padsabove & below the spring units).

Pre-requisites for releasing the springs & subsequent leveling

Completion of installation of all TG components.Erection completion of all the connected piping (Viz. MS, CRH, HRH,

Extraction, gland steam, leak-off, drains etc.), and after floating these pipeson their respective hangers / supports.

Completion of insulation work on turbines & piping as per Sl. No. 2.After ensuring that the deck is free to move without restriction.Hotwell is filled with water unto normal level.

CW pumps in operation, maintaining design flow through condensers.LPH 1, which is inside condenser, has its water boxes & tubes filled with


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water.Generator hydrogen coolers & piping filled with water / cooling water system isservice.Cladding if envisaged has been erected.

Condenser springs are in released condition.

In other words, ensure before releasing the springs that the deck has been loaded

to its design capacity.

Activities on spring units after releasing the springs

The deck is floated using hydraulic jacks, which are placed between the upper boxor the spring unit and the steel cover plate. Either two / four hydraulic jacks areused for release of the springs. These jacks supplied by GERB, operate in a groupand work with one pumping unit, which is electrically operated.

In accordance with the calculated values, it is decided whether or where further

steel shims should be removed or added.

During releasing of TG deck springs while the additional 5,0 mm shims (foradditional compression) are removed, the catenaries of the machine is to be

achieved within the tolerance prescribed with the help of TG deck springs. This isdone by adjusting the shims and afterwards only the rotor alignments should betaken up. Any minor variation in catenary left after releasing of TG deck springs maybe adjusted at the bearings for achieving the correct values.

(The ready-made galvanized shims/steel shims are supplied in required sizes alongwith spring units in 3,00 mm and 2 mm thickness, so an adjustment of up to 1,00

mm is possible in spring units.)

4.1 The heights of TG deck springs are taken on four corners near the

springs. Here some punch mark may be provided on all springs so thatmeasurements are taken at the same place every time.

Check before starting the machine operation

The nuts of the prestressing bolts should be screwed down to the bottom end of the

bolts.

Care to be taken while removing a major load the deck during maintenance

machine.

If major parts of the machine are removed, such as casings, rotors, etc. it isnecessary to lock the spring unit-s again by hand. When these machine parts arereplaced unlock the spring elements again.

Maintenance of spring units

No special maintenance is necessary. Check only, if there is any corrosion. In case

of corrosion, paint the unit with anticorrosive paint (such as Coro-Cote). No water orother liquids should get into the viscodampers.


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Replacement of spring units

The supplier claims that springs of the supporting system have very remotepossibility of breakages.

The replacement, if needed, can be done by compressing the springs of defectiveunit, using the hydraulic jack system.

After compression, the unit is locked by the side bolts. Then the element can be

removed & replaced.

Load sharing by condenser springs and TG deck springs

All the loads to which condenser springs are subjected with during neckwelding of the condenser with LPC are shared by condenser springs.

(Dead weight of condenser, water boxes, tubes, stiffener pipes, normal level

of water etc.)

Weight of the static components, dynamic loads on the deck condensercooling water static & dynamic loads are taken by deck springs.

Whether TG deck can be floated under the Circumstances when CW pumps arenot available?

Answer is yes, it is possible. (Ref. Directive PS/TSX/T dtd 12.06.97)

Often, the situation arise when CW pumps commissioning gets delayed on account

of various reasons.

The steps are

1) Ensure all the components have been erected on TG deck as per detailsgiven in Sl. No. = 10.

2) In the absence of non-availability of CW pumps, the calculated quantityof water can be filled in the steam space of condenser. This is normally

equal to the weight of circulating water in the condenser tubes & waterboxes plus the weight of condensate in the hot well unto normal level.

3) Keep the condenser springs released.

4) Float the deck as per normal procedure described earlier.

Important Note:

1) The need to check the alignment by running CW pumps is to take corrective

measures if the dynamic load of running water changes the alignment in additionto the static load of water in condenser.

2) By simulating the water condition in the condenser, the effect of static load istaken care of but the effect of dynamic load is still pending. This can however be

checked after the availability of CW pumps by reopening the couplings.


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3) Under such conditions, without releasing of the springs, the alignment of allthe rotors can be done and reaming / honing including fitting of all final couplingbolts can be completed. The coupling bolts need not be elongated at this stageand when all the conditions can be fulfilled (as per sl. No. 10), the alignmentscan be checked & corrected.

Effect on machine vibrations when loads are withdrawn from the deck while

machine is in operation.

The spring elements system is designed for abnormal conditions, which may arise

during the operation of the machine. Some times one half of the condensers needisolation while M/c is in operation. On some occasions, when M/c is running on load& total Ac failure takes place, apart from the steam loads, sudden withdrawal ofcooling water loads of very high magnitude is observed from the TG deck.

Various modes were tried during the load operation of Dahanu units. No appreciablechange in vibration pattern noticed during these modes of operation. Moreover due

to various problems in condenser cooling water ducts/ (BSES scope), a constantvariation in the condenser cooling water loads on TG deck noticed during high tides

& low tides regularly. This change in load also does not cause any significant changein vibration pattern.

Prestressing of spring units:

The spring units are delivered to site slightly prestressed for the purpose oftransportation.

The required prestressing of the springs (based on column load) is done at

site before their installation in position.Prestressing corresponds to

a) Static deflection of springs due to operation loads.

b) An additional deflection of 5 mm to cover temporary over loadingduring the machine installation.

This additional deflection of 5 mm is equalized by shims on top of the springunits, which are removed when the prestressed units are released.

(This means, that the top level of foundation is 5 mm lower and will reach final

level after releasing spring units).

A note on additional loading on springs by providing 5 mm shims

The springs units are not only pre-compressed for Calculated load of the machinebut it is further pre-compressed to prevent the loosening of the spring duringinstallation of the equipment due to unforeseen additional loads. If majorvariation in calculation of load over the spring units is not expected then an

additional compression of 5.00 mm is sufficient for this purpose. These shims areremoved at the time of loosening of spring elements before final alignment of the

machine. It is also not necessary to remove this complete 5.00 mm shims foreach spring unit and the same may vary form spring unit to spring unit depending

upon the variation of column level / elevation and variation in level of springcover plate etc.

The spring units are compressed in special steel frame with hydraulic jacks.


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The elements are locked in this position by the side bolts into eh spring units.

(Steel frame and jack are supplied by GERB).


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1.0 Mounting of spring units:

1.1 Before the spring units are mounted, the supporting beams columns aremarked where the units are to be located, as per the drawing.

1.2 One adhesive resilient pad is placed on the surface of the supporting beamcolumns for each element. The pad has same size as the contact area of theelement.

1.3 The prestressed spring units are placed on top of the adhesive pads with acrane. Threaded holes are provided on top of the spring units to use eye-bolts (M-20).

(Caution: The heads of the prestressing bolts must be on the upper side!!!)

1.4 Like a sandwich a stack of adhesive pad steel shim and another adhesive

pad is laid on top of the spring units, as per calculations.

(Adhesive pads are used to avoid movement of the spring units/shims

during operation of the machine)

1.5 If the level of the upper adhesive pad is not in accordance with the drawingthe difference should be corrected by reducing or adding steel shims.

1.6 Then, a plastic foil is wrapped around the spring units to give protection

against concrete milk or dust.

1.7 Finally, the cover steel plates are placed over the spring units. The cover

steel plates will stay in position after-wards and will not be removed. It willserve the purpose of equal distribution of pressure, when jacks are used forthe leveling procedure or for the release of the spring units.


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(Caution: The bottom sides of the steel plates and the bottom sides of thepedestal (deck) must be on the same level).

2.0 Condition of the springs when machine is assembled

2.1 Springs remain in locked prestressed condition when machine isassembled.

2.2 During the installation of the machine the deck may settle 1-1.5 mm

without prestressing bolts of the spring units becoming loose.

(The reason is a possible plastic compression of the adhesive resilient padsabove & below the spring units).

3.0 Pre-requisites for releasing the springs & subsequent leveling

1. Completion of installation of all TG components.

2. Erection completion of all the connected piping (Viz. MS, CRH, HRH,

Extraction, gland steam, leak-off, drains etc.), and after floating these pipes ontheir respective hangers / supports.

3. Completion of insulation work on turbines & piping as per Sl. No. 2.

4. After ensuring that the deck is free to move without restriction.

5. Hotwell is filled with water unto normal level.

6. CW pumps in operation, maintaining design flow through condensers.

7. LPH 1, which is inside condenser, has its water boxes & tubes filled withwater.

8. Generator hydrogen coolers & piping filled with water / cooling water systemis service.

9. Cladding if envisaged has been erected.

10. Condenser springs are in released condition.

In other words, ensure before releasing the springs that the deck has been loadedto its design capacity.

4.0 Activities on spring units after releasing the springs

The deck is floated using hydraulic jacks, which are placed between the upper box

or the spring unit and the steel cover plate. Either two / four hydraulic jacks areused for release of the springs. These jacks supplied by GERB, operate in a group

and work with one pumping unit, which is electrically operated.

In accordance with the calculated values, it is decided whether or where furthersteel shims should be removed or added.


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During releasing of TG deck springs while the additional 5,0 mm shims (foradditional compression) are removed, the catenaries of the machine is to beachieved within the tolerance prescribed with the help of TG deck springs. This isdone by adjusting the shims and afterwards only the rotor alignments should betaken up. Any minor variation in catenary left after releasing of TG deck springs maybe adjusted at the bearings for achieving the correct values.

(The ready-made galvanized shims/steel shims are supplied in required sizes alongwith spring units in 3,00 mm and 2 mm thickness, so an adjustment of up to 1,00

mm is possible in spring units.)

4.1 The heights of TG deck springs are taken on four corners near thesprings. Here some punch mark may be provided on all springs so thatmeasurements are taken at the same place every time.

5.0 Check before starting the machine operation

The nuts of the prestressing bolts should be screwed down to the bottom end of thebolts.

6.0 Care to be taken while removing a major load the deck during

maintenance machine.

If major parts of the machine are removed, such as casings, rotors, etc. it isnecessary to lock the spring unit-s again by hand. When these machine parts arereplaced unlock the spring elements again.

7.0 Maintenance of spring units

No special maintenance is necessary. Check only, if there is any corrosion. In caseof corrosion, paint the unit with anticorrosive paint (such as Coro-Cote). No water orother liquids should get into the viscodampers.

8.0 Replacement of spring units

The supplier claims that springs of the supporting system have very remotepossibility of breakages.

The replacement, if needed, can be done by compressing the springs of defective

unit, using the hydraulic jack system.

After compression, the unit is locked by the side bolts. Then the element can beremoved & replaced.

9.0 Load sharing by condenser springs and TG deck springs

9.1 All the loads to which condenser springs are subjected with during neckwelding of the condenser with LPC are shared by condenser springs.

(Dead weight of condenser, water boxes, tubes, stiffener pipes, normal levelof water etc.)

9.2 Weight of the static components, dynamic loads on the deck condensercooling water static & dynamic loads are taken by deck springs.


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10.0Whether TG deck can be floated under the Circumstances when CW pumpsare not available?

Answer is yes, it is possible. (Ref. Directive PS/TSX/T dtd 12.06.97)

Often, the situation arise when CW pumps commissioning gets delayed on accountof various reasons.

The steps are

1) Ensure all the components have been erected on TG deck as per detailsgiven in Sl. No. = 10.

2) In the absence of non-availability of CW pumps, the calculated quantityof water can be filled in the steam space of condenser. This is normallyequal to the weight of circulating water in the condenser tubes & waterboxes plus the weight of condensate in the hot well unto normal level.

3) Keep the condenser springs released.

4) Float the deck as per normal procedure described earlier.

Important Note:

1) The need to check the alignment by running CW pumps is to take correctivemeasures if the dynamic load of running water changes the alignment in additionto the static load of water in condenser.

2) By simulating the water condition in the condenser, the effect of static load is

taken care of but the effect of dynamic load is still pending. This can however bechecked after the availability of CW pumps by reopening the couplings.

3) Under such conditions, without releasing of the springs, the alignment of allthe rotors can be done and reaming / honing including fitting of all final couplingbolts can be completed. The coupling bolts need not be elongated at this stageand when all the conditions can be fulfilled (as per sl. No. 10), the alignmentscan be checked & corrected.

11.0Effect on machine vibrations when loads are withdrawn from the deckwhile machine is in operation.

The spring elements system is designed for abnormal conditions, which may ariseduring the operation of the machine. Some times one half of the condensers needisolation while M/c is in operation. On some occasions, when M/c is running on load& total Ac failure takes place, apart from the steam loads, sudden withdrawal ofcooling water loads of very high magnitude is observed from the TG deck.

Various modes were tried during the load operation of Dahanu units. No appreciable

change in vibration pattern noticed during these modes of operation. Moreover dueto various problems in condenser cooling water ducts/ (BSES scope), a constant

variation in the condenser cooling water loads on TG deck noticed during high tides& low tides regularly. This change in load also does not cause any significant changein vibration pattern.

GERB Spring Loaded DECK Inf

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