a case study - ceacea.nic.in/reports/others/hydro/herm/technical2/ts24.pdfr, m&u of generating...

R, M&U OF GENERATING UNITS

OF NPH

A Case Study

R, M&U of Generating Units of NPH - A Case Study

KARNATAKA POWER CORPORATION LIMITED(KPCL)

• STATE OWNED PUBLIC LIMITED COMPANY IN THE

BUSINESS OF GENERATION OF ELECTRIC POWER.

• THE COMPANY HAS A WORK FORCE EXCEEDING

5000 PEOPLE INCLUDING ABOUT 1800 ENGINEERS.

• THE CUSTOMERS OF KPCL ARE HESCOM, BESCOM,

GESCOM, CHESCOM AND MESCOM FOR SALE OF

ENERGY.

• KPCL HAS A TOTAL INSTALLED CAPACITY OF

ABOUT 7223.9 MW CONSISTING OF HYDRO-

ELECTRIC STATIONS, THERMAL POWER PLANTS,

WINDMILLS AND SOLAR PV PLANTS.

HYDRO THERMAL SOLAR WIND


Thermal Units at Yermarus are

at final stages of commissioning

TOTAL KPCL-7223.905 MW

HYDRO3667.35 MW

THERMAL3528 MW

SOLAR24 MW

WIND4.555 MW

3667.35

3528

24

4.55528.555

Hydro

Thermal

Solar

Wind

RES


KPCL has 21 Hydro Power Stations:

Shivasamudram - 116 years

Shimsha - 76 years

MGHE - 68 years

SGS - 52 years

Bhadra - 54 years

Munirabad - 54 years

NPH - 38 years

Linganamakki - 38 years

Supa - 31 years

Varahi - 27 years

Mani - 23 years

Kadra - 19 years

Kodasalli - 18 years

Gerusoppa - 15 years

Almatti - 12 yearsShivasamudram Power House

R, M&U of Generating Units of NPH - A Case Study• Kalinadhi Hydro Electric Scheme was

developed in stages.

First stage-

6x135MW at Nagjhari Power House.

2x50MW Supa dam power house.

Second Stage:

3x40MW at Kodasalli Power House

3x50MW Kadra Power House.

• NPH -Commissioned during 1979-84

• Turbine: Vertical Francis.

• Rated rpm: 375

• Rated Net head : 347m

• First time 375 rpm units with Francis

turbine installed.

• Very few units with 375rpm Francis type

turbines were in operation at that time.

• Design energy of the project was 4082

MU.


Performance of the units

• Generating units were prone to vibration

since commissioning

• Detailed analyses to find the cause of

vibration were carried out

• Various experts were involved in analyzing

the problems

• Tests conducted by Dr. Mahern Holtz of

Hamberg University during 1984 showed

that critical speed is in the vicinity of rated

speed of 375 RPM

R, M&U of Generating Units of NPH - A Case StudyAnalysis of the results

The analyses by various experts indicates that transient vibrations are basically due to following reasons:

• Periodical residual mechanical and magnetic unbalanced pulls causingexcitation and resonance to the rotor system at sub-synchronous speeds

• Unacceptable Stator and rotor form, resulting in very high UMP (unbalancedmagnetic pull)

• Resonance close to normal speed due to insufficient stiffness of bearingsupport structure

• Drawal of higher than designed/rated excitation current at 135MW. Excitationcurrent was exceeding 1250 Amp as against rated 1140 Amp for 135 MW

• The stiffness of present bearing brackets are as follows:

Upper Bracket 0.2x 109 N/m

Lower Bracket 0.5x109N/m

• Recommendations: Stiffness of both upper and lower brackets have to behigher than 1.0x109 N/m and UMP to be reduced by improving the circularityof stator and rotor

R, M&U of Generating Units of NPH - A Case StudyExpert committee consisting of members from CEA, OEM and KPCL recommended

to take up Renovation, Modernization & Uprating of one unit on a pilot basis and

carry out the modifications based on the results of analyses.

R, M&U OF U#1,2&3

• Subsequently, Contract was awarded to the OEM for R, M & U of one unit at

NPH on 05.09.1992

• Since, Unit-2 was under shut down due to stator coil failure, it was taken up for

R, M & U works on 10.01.1994 at a cost of Rs.798.45Lakhs and re-commissioned

on 03.05.1995 (16months)

• Major works carried out includes replacement of stator, modification of top

bracket housing and arm assembly, guide bearing support ring for bottom guide

bearings, slip rings, etc


• Based on the results of R, M & U of Unit-2, R, M & U of units 1& 3 was

taken up in the second phase and OEM was awarded the Contract

through competitive bidding at a total cost of Rs.1639 Lakhs for two

units.

• Scope of work mainly covers only generator portion as done for unit-2.

• Turbine: Self lubricated bushed were provided. No major works on turbine

carried out.

Additional HP lubrication system provided which would operate whenever

thrust bearing temperature shows raising tendencies.

The performance of the Units after R, M & U is generally satisfactory.


R, M&U OF U#4,5&6

• Based on the experience of the R, M & U of Units-1, 2 & 3, R, M & U of

Unit-4, 5 & 6 was taken up in the next phase in 2003

• Contract was awarded to a Non-OEM through an ICB

• Modernization of Governors and Static Excitation systems were also

taken up.

• Total cost for lakhs of supply was Rs.2430Lakhs and Rs. 790 lakhs for

erection, testing and commissioning of equipment

• Delivery period was 33 months (Staggered deliver period for three

units) and erection period was 8 months from handing over of each

unit

• It was planned to take up works on one unit at a time so that other

units are available to support the grid and optimum utilization of water

R, M&U of Generating Units of NPH - A Case StudyNew technologies adopted for R, M&U of U#4,5&6

• Floating rim technology used instead of the earlier floating Rim technology for

rotor spider.

• Stator frame supplied in 3 segments and built as joint less ring at site to eliminate

core sector joints and to improve rigidity of stator core

• The stator core supplied of silicon alloy sheet steel(low loss material)

• On line monitoring system used to monitor the Air gap, vibration and partial

discharge of the units

• Epoxy insulation Disc between thrust collar and runner disc provided to avoid entry

of leakage current to runner disc

• Over-speed device with latest technology

• Digital excitation system

• Digital Governor system

• Flow measuring device


R, M&U of unit-4

• Dynamic Shaft Analysis was conducted at NPH during

December-2003.

• Contractor recommended to have modified rotor structure

with rigid rim technology instead of existing floating rim

technology for improving performance and reducing

vibrations.

• The subject was discussed with experts in the field including

experts in IITs.

• Based on the studies, it was decided to retain the exist

rotor spider.


NEW MODIFIED ROTOR SPIDER

R, M&U of unit-4

• Erection works on Unit-4 was taken up from

18.03.2005.

• After dismantling, ND tests on rotor spider

showed 40 Nos of weld cracks

• Considering need for long term performance,

detailed review to reduce vibrations,

modification of rotor structure was taken up

and it was decided to provide new modified

rotor spider for shrunk fitting on rotor shaft.

• Price of Rs.837 Lakhs for supply and Rs. 93

Lakhs for erection for all 3 units during June

2006

• Delivery period for 4th unit was 9 months

• Unit No.4 commissioned on 28.02.2008 after

completion of R, M & U works


Rotor RimBuilding

Pre-heating ofRotor Spider

Lifting ofRotor Spider

Shrink Fitting ofRotor Spider withGenerator Shaft

Various stages during Rotor Rim Building

1

2

3

4


R, M&U of unit-4

• Performance of unit was satisfactory withVibration levels within limits.

• But oil splashing problem from UGB oil sleeve noticed.

• Modifications carried out on thrust collar assembly and other accessories

in the Bearing Housing to solve the problem.

• Total time period taken for R, M&U works is 35 months.

• Main reasons for delay :

• Major defects noticed after opening of the unit.

• Non-availability of machine drawing,

• Time taken for reverse engineering,

• Manufacturing of equipment after opening of unit for supply of new modified

rotor spider as cracks were noticed only after opening unit, etc.


R, M & U of unit-5

• U#5 was handed over from 1.05.2009

for erection and commissioning

works.

Problems in U#5

After opening of the unit, the following

observations were made:

• Generator Shaft was found with

varying diameter from DE side to

NDE side

• During inspection, undercuts found

due to welding of plates near aeration

holes at 4 places on NDE side flange

of turbine shaft (rotor shaft coupling

side)

• Pitting in Lower Labyrinth

Welded Region of

Turbine Shaft

Generator

Shaft


R, M & U of unit-5• The inner diameter of the MIV Main

seal found corroded, ovality (2 to 2.5

mm) and found in damaged condition

• Eccentric and Concentric Pin for GV

Lever and Regulating Ring were found

eroded

• Coupling bolts and nuts between

Turbine and Generator Shaft Coupling

were found damaged

Coupling Bolts

Eroded Central Part of Gland

Seal Assembly of MIV Main seal


R, M & U of unit-5

• It was necessary to repair

• Labyrinth rings,

• replace housing of shaft gland seal,

eccentric pins for guide vane lever

and regulating rings, rotor rim studs,

etc.

• Additional price of Rs.99.9 Lakhs

with a delivery period of 6 months

for supply and erection period of 3

months there after

• Unit – 5 was synchronized with the

grid after the completion of R, M&U

works on 19.03.2011

R, M&U of Generating Units of NPH - A Case StudyR, M & U of unit-6

• Based on experience of unit 4 & 5 and inspection of Unit-6 carried out

in dewatered condition(Without dismantling).

• Additional orders were placed for supply of pivot ring based on

inspection for unit-6 to save time

• Unit-6 was handed over on 20.12.2012

• After opening of the unit, ND tests were carried out

• ND test results showed presence of crack in turbine shaft, erosion

beyond permissible limits in top cover, high erosion and corrosion in

runner and other under water parts


NDT test results

DP teston turbine shaft

Damages observedin poles

Runner underDP test beforerefurbishment

Cracks observedduring MP teston pole end plates


Some of the Eroded/Damaged parts after opening of unit – 6

Regulating ring

Shaft Sleeveplate assembly

Labyrinthring

Base metal erosionnear labyrinth andliner plate area


List of Eroded/Damaged parts after opening of unit – 6

GV body pitting

Guide Vane Levers

Pivot Ring Turbine Shaft


List of Eroded/Damaged parts after opening of unit – 6

Regulation Ring Metal chipped out from vane exit area of Runner.

Top Cover

Shaft gland housing Base metal erosion near labyrinth and liner plate area

Eroded top cover

Top Cover


Additional orders placed for U#6 after inspection of components and discussions with OEM:

OEM

• Repairs to turbine shaft and supply of modified shaft sleeve in August2013

• Supply of new top cover in October 2013. Top cover has been supplied in6 months

Contractor

• Refurbishment of runner

• Refurbishment of labyrinth ring

• Supply of new epoxy runner insulation disc

• Line boring works for assembly of top cover and pivot ring


Components after refurbishmentt

MIV Guide Vane Levers

New top Cover supplied by OEM New Pivot Ring

Regulating ring


Pivot ring

• Order placed on Contractor forsupply of pivot ring

• Noticed difference in flangethickness by 4.5mm duringinspection

• Contractor proposed to provideadditional plate of 4.5mm thicknessof stainless steel-304 with rigidcounter shank screw locking

• Contractor informed that theywould fillet weld the SS plate withthe base of pivot ring on the wholeperiphery New Pivot Ring

Old Pivot Ring


Top Cover

• It was observed that the base metal has

eroded more than 75% at critical areas and

most of the eroded areas were beyond

refurbish/repair.

• Contractor and OEM recommended for

replacement of top cover.

• Both recommended for replacement of

top cover.

• The offer obtained from OEM was less and

also time period offered was also less.

• Top Cover was supplied in six months New Top Cover

Old Top Cover


Turbine Shaft• 2 Nos. cracks of size 170mm and 42mm found in

Shaft at shaft seal machining area during DP test

• Around 7mm deep penetration of crackobserved through traverse length of 50 – 60mmat Shaft sleeve seating area through Ultrasonictest

• OEM was consulted in the matter

• OEM informed that the defective portion ofturbine shaft would be machined and diameterof the shaft shall be reduced in the entire portionwhere the shaft sleeve is to be fitted

• New SS shaft sleeve with reduced ID shall befitted on the shaft & its OD machined

• Additional order placed on OEM forrefurbishment of turbine shaft along with new SSshaft sleeve

• Time taken was about 4 months

Turbine shaft under DP test

R, M&U of Generating Units of NPH - A Case StudyRunnerAfter opening of unit– 6, the following

observations were made:

• Multiple pitting on runner vanes

• Metal chipped out 30 to 50mm from

Runner vane exit area

• After NDT tests at factory, it was observed

that runner had 236 indications on outside

of 4-30mm and inside 85nos. indications of

4-20mm

• Both OEM and Contractor recommended

for replacement of runner

• After detailed studies and need to put back

the unit at the earliest, additional order for

refurbishment of runner was placed on the

Contractor.

Turbine shaft under DP test

Runner after

refurbishment

Metal Chipped out

R, M&U of Generating Units of NPH - A Case StudyLine boring Works

• Challenges:

Stay ring refurbished in site.

New Pivot ring with tolerance for line boring – 0.25mm – Machined in separate

CNC machine.

New top cover with tolerance of 2 mm for line boring – Machined in separate

CNC machine.

Refurbished runner

Observed that dia of top cover at regulating ring seating area was excess by 6mm.

• Pilot holes were provided for doweling.

• It was necessary to have proper matching for concentricity of holes with

different parts and matching of dimensions of holes with close tolerances –

0.05 mm/ m.

• An additional order placed for line boring works – order value 24 Lakhs.

• Delivery period – 45 days.

R, M&U of Generating Units of NPH - A Case StudyMatching of top cover and pivot ring at site

• This is a rare case of matching different components to achieve

required results

• Top cover and pivot ring were manufactured by two different

machines. Re-engineering took considerable amount of time

• The clearance between Labyrinth ring and top cover was

maintained by 4 dowels and complete load of static labyrinth

taken by bolts and transferred to top cover

• Unit – 6 was synchronized to grid after completion of R, M&U

works on 25.11.2015

• Main reason for delay is non-availability of as built drawings and

surprises noticed after opening of the unit

• Higher capacity oil coolers provided to bring down thrust

bearing temperature and its performance after commissioning is

satisfactory


Benefits Derived after R,M&U Works:

• Addition of 90 MW peaking capacity to the grid

• Life extension of 10 to 15 years

• Problem of over drawal of field current has been resolved by

achieving circularity in stator and rotor forms

• Performance of the unit with respect to vibration and

temperature rise of thrust bearing is generally satisfactory and

is under observation

• Online monitoring of vibration levels and PD Analyser has

become a safety tool to monitor the units at any instant of time


CONCLUSION

• R, M & U of the units provide opportunity for correcting some of the

inherent problems and adopting new technology

• Challenging considering the requirement to match with many old

parts for which neither machine drawings nor design calculations are

available

• Undertaking timely RM&U & Life extension programme, life of

generators has been extended

• Major works has been carried out only in Generator portion and

higher output is achieved through higher guide vane opening utilizing

the margins available in old machines

• It is clear from the experience of R, M & U that extent of

refurbishment/replacement required in respect of turbine could not

be assessed before opening of the unit


CONCLUSION

• After opening of the unit, reverse engineering will take considerable

time which will affect the schedule of erection and commissioning

• OEM will have the advantage of having the initial designs and hence has

the advantages with respect to manufacturing and delivery of new

components

• NON-OEM manufacture may have a different solution for solving the

problems. It may be difficult to bench mark the prices especially with

respect to refurbishment works and with two differing technologies.

These aspects have to be factored while executing the works to

adhere to planned schedule


CONCLUSION

• We have taken up preparation of DPR for R&M works of turbine of

Unit-1,2 & 3 in association with IIT Roorkee.

• DPR prepared and submitted to Hon’ble KERC.


Runner

Rotor

Turbine shaft


Cross section of turbine with location of runner and top cover

Runner

Top Cover

Pivot ring

THANK YOU

a case study - ceacea.nic.in/reports/others/hydro/herm/technical2/ts24.pdfr, m&u of generating...

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