Innovative Design Features of Turbines for Hydro Projects

International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
INNOVATIVE DESIGN FEATURES OF TURBINES FOR HYDRO
PROJECTS LOCATED IN HIMALAYAN REGION
C K Jain, Alstom India Limited
Hydro projects located in sub Himalayan region (Nepal, India and Bhutan etc.) impose some
unique challenges for design and supply of hydro plant equipment. These challenges can be
regarded as below:
1
2
3
4
5
Weak land strata and geological surprises (complex civil design)
Quality of water (presence of hard silt particles)
Difficult terrain and approach roads (transportation dimensions & weight)
Maintenance problems (assembly and dismantling issues)
Environmental friendly solutions (no pollution to river water)
Above challenges constrain equipment suppliers to great extend and compel them to innovate
and offer new solutions. Major constraints for design of equipment perceiveddue to above
challenges are:
•
•
•
•
•
•
•
Small Package size due to transportation limitations.
Compact layout of equipment to reduce power house cavity size.
Access issues due to the remote and underground location of the power house
Specific assembly and dismantling requirements.
Stable turbine governing operation against given water conductor system
Mechanical design of parts to protect against river water containing high silt
abrasive particles.
Maintenance friendly design of assemblies.
Alstom with its century old experience and feedback of numerous projects located in mountain
regions world wide has come out with some innovative and proven solutions for hydro plant
equipment to overcome these challenges and constraints.
Some of the innovative solutions introduced by Alstom recently for better performance of
hydro plant equipment are explained in this paper. Most of the hydro machines in Himalayan
region falls under high head and medium head category therefore solution related to Francis
and Pelton turbine are described:
1.
2.
3.
Equipment and power house layout design - to offer compact equipment design and
lay out to minimize civil instabilities.
Stable turbine operation - to offer versatile hydraulic design for given water
conductor system considering large variation in head and discharge.
Design of turbine parts to resist high silt abrasive particles. Monsoon flow will
contain high silt abrasive particles with majority of quartz. Useful life of critical
components to be enhanced with
a. Protective coating on critical turbine parts
b. Hydraulic profiles to offer minimum resistance to silt abrasion.
339
ICHPSD-2015
4.
5.
Environmental friendly designs - to offer minimum pollution to river water
Recent development in Pelton turbine
Each of constraint is discussed in detail with proposed Alstom solution
1
Equipment and power house layout design
Alstom solution
•
For under ground power houses it become more obvious to provide a robust and
compact equipment design and power house layout. Some of the innovative features
developed by Alstom are
A
B
C
A-
- Thrust bearing on turbine head cover
- Ring gate in place of main inlet valve
- Compact draft tube design
Thrust bearing on turbine head cover supporting cone
This concept is used for Francis and Kaplan turbine both. Alstom has long experience for
supply of thrust cone .with series of experiments, site feedback and design modification using
modern calculation tools, we have thoroughly optimized thrust cone design. Alstom has
supplied since 1955, more than 350 units since 5 years, more than 22 units (with improved
design).
Fig. 1: Proposed thrust cone system has following advantages
340
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
•
•
•
•
•
•
Up to 30% reduction in height (btw turbine and generator C/L)
No separate foundation for thrust bearing
Shorter shaft  Betterdynamic behavior
Higher stiffness  Higher natural frequency
Thrust loads balance hydraulic forces
Good accessibility + maintenance of thrust bearing
Some design aspect
The cone is simple structure that represents high axial strength.It is fixed on head cover by
bolts and pins.It has one or two access opening for shaft seal and guide bearing maintenance.
Analytical and FE calculations are done to check deformation of thrust plate (where thrust
bearing is supported).Design have different options, to control deformation at thrust plate,
cone can be reinforced. Operating ring can be conveniently placed on thrust cone to make
turbine arrangement more compact.
Fig. 2: Thrust cone deformation during transient condition
Fig. 3:
341
ICHPSD-2015
B-
RING GATE
Ring gate is a cylinder placed between the stay ring and the distributor to cut off the flow of
water.It replaces the traditional main inlet valve in the power house.Ring gate operating is
controlled by the governor through synchronized hydraulic servomotors.The ring gate
geometry is defined by a series of model and proto tests. In past, synchronization of hydraulic
cylinders were achieved though mechanical synchronization. With recent development
hydraulic cylinders of ring gate are synchronized by electronic control system. Now it is
possible to synchronize movement of all cylinders within 1 mm.
Advantages
•
•
•
•
•
•
•
•
•
Optimization of the width of the power plant, resulting in to lower civil
engineering costs.
Elimination of a separate MIV gallery.
Lower handling and crane costs.
Cost of ring gate equipment is lower than MIV.
Zero head loss with the ring gate (as it is out of the flow path) in operating
condition improves efficiency of turbine.
Hydro static testing of spiral casing can be performed with the ring gate thus
eliminating a dummy distributor.
Self closing of the ring gate can be achieved (by gravity) in the case of oil
pressure failure.
Improves performance of the turbine during synchronous condenser operation.
Cost effective alternative to large size spherical valve.
Fig. 4: Cross section of plant with ring ate
342
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
Design aspect
Basic technology of Ring gate was developed by Alstom some 75 years ago (Alstom product
patent (1947 for Ring gate).Alstom carried out series of model tests and proto tests for La
Grande 4 (1976-1980). More than 40 units ring gates are commissioned from 1962 to 2013.
Following are the design requirements for ring gates :
Opening : always in still water (without water flow)
Normal closure : in still water or under full turbine discharge or under partial discharge due
to 1 wicket gate remained in open position
Free wheel closure :Same closing conditions as for the normal closure but with 1 servomotor
put in “freewheel” condition due to its desynchronization detected by the electric control
system TSLG
Closure stopped by a foreign body : TSLG detects the desynchronization of servomotors
and re-open a little the Ring Gate then try again to close and if the Ring Gate is again stopped
then the Ring Gate is immobilized/locked in this position
Closure “by Ring Gate weight” without synchronization of servomotors: ONLY in case of
a breakdown of the Electric Control system (TSLG) and
•
•
either in still water
or under full turbine discharge
For above two conditions, mechanical guiding of the body inside the stay vanes will allow the
Ring Gate to close properly without the need of synchronization as the hydraulic loads applied
on the Ring Gate body are symmetrical.
Ring gate, hydraulic cylinders and its operating mechanism are designed to fulfil above design
requirement. Complete design philosophy of ring gate (mechanical design, hydraulic design,
oil pressure system, control system) was validated by extensive site tests for Dong Quing and
AHai projects of China.
343
ICHPSD-2015
Fig. 5: Ring gate between stay ring and head cover / bottom
Fig. 6: Inside of turbine pit with ring gate servomotors
344
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
Fig. 7: Site measurement of ring gate closing time and synchronization error
C-
COMPACT DRAFT TUBE DESIGN
For under ground power houses, excavation is a big concern with client . Conventional draft
tube requires huge cavity for installation. Concrete wall between two units of draft tube
sometimes do not provide sufficient strength for civil load transfer. Alstom has developed a
circular draft tube in place flaring conventional draft tube.. It has following advantages:
•
•
•
•
•
Civil excavation at site can be reduced substantially
Most suitable for underground power house WITH LONG GALLERIESas length of
circular draft tube ( with steel portion ) is large to accommodate admissible water
velocity at the exit of steel liner.
Easy manufacturing, transportation and erection at site
Improves delivery time
Improved performance of turbine for wide range of operation
Hydraulic design of circular draft tube has been developed by CFD analysis results were
proved in model testing and validated at site.
345
ICHPSD-2015
Fig. 8 (a): Convention draft tube
2.
Fig. 8 (b):Circular draft tube
Stable turbine operation
To offer versatile hydraulic design for given water conductor system considering large
variation in head and discharge.
Alstom solution
Ideally Francis runner gives stable and satisfactory performance for regime of 50 to 110 %
of rated load . With present scenario where clients wants optimum utilization of available
discharge by generating power at low loads, efforts are placed to develop suitable Francis
runner model which can be operated at low loads under less discharge condition.
Alstom R &D is in process of developing new solution to ensure stable operation of turbine
at low discharge and low loads conditioncontinuously at rough zone ( extended part load
operation). Runner profile is first developed analytically (by CFD analysis / FE analysis)
andchecked for structural stability for life time. During model testing major hot spots in
runner profile are implanted with strain gauges to determine mechanical behavior during
dynamic conditions and simulate operating conditions. Suitable modifications are carried out
on blade profile based on test results.
Model testing results also validated by prototype tests of runner at site.
346
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
Fig. 9: Extended operating zone on hill chart
Fig. 10: Extended operating zone on hill chart
347
ICHPSD-2015
Fig. 11: Various runner models under development
3.
Design of turbine parts to resist high silt abrasive particles
Monsoon flow will contain high silt abrasive particles with majority of quartz. Critical turbine
parts should be suitable designed and coated to minimize erosion impact.
Alstom solution
1
2
3
Continuous development of new hydraulic profiles to offer minimum resistance to silt
abrasion.
Selection and validation of protective coating on critical turbine parts depending on
various project parameters influencing behavior of coating.
Development of online silt measurement device.
Dedicated silt erosion simulation test rig facility has been developed to carry out following
analysis
-
to evaluate erosion rate and validate consistency of erosion resistance.
to carry out standard coting qualification test (adhesion, porosity, hardness…).
To develop good quality of coating and consistency through extensive testing and
stringent quality check at various stages and also by preparing test coupons for
prototype product qualification.
Erosion Phenomenon is analyzed based on following parameter to establish life span of
existing coating solutions.
•
•
Fluid Pressure
Jet velocity
348
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
•
•
•
•
•
Angle of impingement
Duration of tests
Silt particles concentration
Silt particles size
Silt particleshape
Fig. 12: Erosion test rig
4.
A B -
Environmental friendly designs
Alstom solution
Water lubricated turbine bearings
Self lubricated bushes for guide vanes and inlet valve trunnion
A -
Water lubricated bearing
Design features
•
•
•
•
•
•
•
•
Most suitable for shaft dia ranging from 500 mm to 1500mm
Water is supplied to bearing shell through 6 or 8 pockets provided with orifice plate
Bearing ID and shaft sleeve are hard coated
Clean and filtered water supply for bearing lubrication and cooling (<90microns)
Requirement of discharge ( 1~3 l/sec) and pressure (penstock pressure) cooling water
is quite less.
Pressurised water flows around bearing surface ensures bearing stiffness.
Radial offset of shaft and pressure variations in pockets brings shaft on axis.
Inflatable air seals provided at the bottom of bearing shell can be applied during
maintenance.
349
ICHPSD-2015
Fig. 13:
ADVANTAGES
•
•
•
•
•
Profitable environmental friendly solution
Replaces bearing & shaft seal
No consumption or replenishment of oil
Lower friction losses than traditional oil bearing
No cooling system required (pumps, exchangers, cooling water circuit, safety
systems...)
Same watering device as for traditional shaft seal
B-
Self lubricated bushes for wicket gates and inlet valve trunnions.
Self lubricated bearings proposed by Alstom are checked and validated at R & D centreat
specially developed test rig. Normally following tests are carried out :
•
•
•
•
•
Validate the main characteristics of bushes available in the market
Compare behaviour of bushes fromavailablevarieties in the market
Classifyspecific use of bushes
Validate new bushes
Feedback fromactual performance of bushes at site
350
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
Fig. 14: Test rig
6
Innovative design of Pelton turbines
Pelton runner is subjected to high fatigue stresses though out its life.
Some constraints for development of Pelton runner
Design
To enhance performance of Peltonmachine ,a careful and systematic analysis is required to
done.
Generally speaking if we intent to improve efficiency ofPelton machine, we need to increase
jet diameter and reduce bucket width. Above feature will lead to high jet load and reduced
attachment of bucket at root this will result into high stresses of bucket at root. Also increasing
number of jets and jet impact per revolution will increase fatigue stress issues.
Manufacture
•
•
•
Complex runner form creates difficulties for casting, NDE and manufacturing.
Materiel defects require extensive repairs which prolong delivery periods and increase
costs.
Problems of casting quality have increased progressively over the last 30 years.
351
ICHPSD-2015
Maintenance
•
•
•
Abrasion and cavitation erosion wears all buckets evenly. Wear can be predicted by
experience and repaired on a programmed basis.
Risk of fatigue cracking requires frequent inspection. Unplanned outages are required
to repair cracks or exchange runner.
Cracking frequency can be related to stress levels in the critical zone at the bucket
attachment, to determine the recommended inspection intervals.
Alstom Solution - Hooped Pelton runner
The Hooped Pelton Runner offers
•
•
•
•
•
•
•
•
•
Resolution of fatigue crack problems
Extended intervals between inspections
Reduced delivery time with reliable material quality
Simpler maintenance operations, more convenient, with less equipment
Accelerated repairs possible if required
Significant savings for bucket renewal compared with a new one-piece runner
Equivalent hydraulic performance
Reduced vibrations
Inter changeability
Fig.15: Hooped Pelton runner
352
International Conference on Hydropower for Sustainable Development
Feb 05-07, 2015, Dehradun
New development for Pelton runners operating under high silt zone
Alstom has developed forged fabricated runners operating under high silt zone. Main
features are
-
Disc is separately forged and rough machined.
Bucket is forged in 2 or 4 parts using die-forging
Buckets are welded with high precision to disc.
Complete assembly is stress relieved & finally machined as per drawing.
Runner is hard coated before dispatched to site.
Fig. 16: Welded runner
CONCLUSION
•
•
•
•
There are wide range of opportunities to improve the global performance of hydro
plant under challenging conditions imposed by Himalayan region.
With global data base for operation of its hydro plants located worldwide, each
problem is carefully captured and analyzed.
Our R& D centers located globally continuously innovates new solutions for
performance improvement of hydro plant based on feedback.
Careful techno–economic investigation also carried out to ensure optimum use of
resources and best return on investments.
353