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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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.
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
• 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 Generating Units of NPH - A Case Study
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 Generating Units of NPH - A Case Study
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.
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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 Generating Units of NPH - A Case Study
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 Generating Units of NPH - A Case Study
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 Generating Units of NPH - A Case Study
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 Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
NDT test results
DP teston turbine shaft
Damages observedin poles
Runner underDP test beforerefurbishment
Cracks observedduring MP teston pole end plates
R, M&U of Generating Units of NPH - A Case Study
Some of the Eroded/Damaged parts after opening of unit – 6
Regulating ring
Shaft Sleeveplate assembly
Labyrinthring
Base metal erosionnear labyrinth andliner plate area
R, M&U of Generating Units of NPH - A Case Study
List of Eroded/Damaged parts after opening of unit – 6
GV body pitting
Guide Vane Levers
Pivot Ring Turbine Shaft
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
Components after refurbishmentt
MIV Guide Vane Levers
New top Cover supplied by OEM New Pivot Ring
Regulating ring
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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
R, M&U of Generating Units of NPH - A Case Study
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.
R, M&U of Generating Units of NPH - A Case Study
Runner
Rotor
Turbine shaft
R, M&U of Generating Units of NPH - A Case Study
Cross section of turbine with location of runner and top cover
Runner
Top Cover
Pivot ring
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