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Head

Department of Mechanical Engineering

Institute of Engineering, Pulchowk Campus

Lalitpur, Kathmandu

Nepal

TRIBHUVAN UNIVERSITY

INSTITUTE OF ENGINEERING

PULCHOWK CAMPUS

DEPARTMENT OF MECHANICAL ENGINEERING

The undersigned certify that they have read, and recommended to the Tribhuvan University, Institute of Engineering, for acceptance, a thesis entitled “Cavitation and Sediment Erosion Analysis in Francis Turbine with Modelling and Simulation (A Case Study of Middle Marsyangdi Hydropower Plant)” by Durga Bastakoti, Harendra Kishor Karn, Indira Khadka and Khadananda K.C. in partial fulfillment of the requirements for the degree of Bachelor of Mechanical Engineering.

Supervisor, Dr. Rajendra Shrestha

Head

Department of Mechanical Engineering

Tribhuvan University, Nepal

External Examiner, Er. Suresh Raut

Assistant Manager

Middle Marsyangdi Hydropower Plant, Lamjung

Committee Chairperson, Dr. Rajendra Shrestha

Head

Department of Mechanical Engineering

Date:

ABSTRACT

The total available energy in Nepal for the year 2010 was 368.27 GWh and 57% of it was supplied by hydropower plants of Nepal. And the total installed capacity of major and small hydropower stations in Nepal is 472.49 MW. Middle Marsyangdi Hydropower Plant is a major hydropower station with total installed capacity of 70MW with an average annual energy generation of 398 GWh.

In MMHP, the critical regions of erosion are sealing region of guide vanes and outlet of runner blades, which was found from modeling and simulation of runner. The main reason is high velocity of sediment laden water, mainly consisting of quartz and feldspar at these regions.

The Air Admission System incorporated in the MMHP is effectively working by admitting air into the draft tube region of runner. The air helps to increase the pressure thereby decreasing the cavitation. Furthermore, the vibration meter reading indicates that the vibration is not increased in part load condition which means the effect of cavitation causing vibration is low.

ACKNOWLEDGEMENT

First and foremost, we express our deepest gratitude towards our Project Supervisor Dr. Rajendra Shrestha, Head, Department of Mechanical Engineering, IOE Pulchowk Campus, for his constant supervision and guidance. Our project would not have been possible without his assistance.

Our heartfelt appreciation goes to Er. Shiva Kumar Shah of Middle Marsyangdi Hydropower Project for his genuine support throughout the project duration. We are really thankful to Associate Prof. Dr. Tri Ratna Bajracharya and Prof. Dr. Bhakta Bahadur Ale for their supportive guidance regarding our project matters.

We are indebted to Prof. Dr. Bhola Thapa, Dean, Kathmandu University and Associate Prof. Dr. Bim Prasad Shrestha, Head, Department of Mechanical Engineering, Kathmandu University, for their valuable suggestions. We are also grateful towards Dr. Hari Prasad Neopane and Er. Biraj Kumar Thapa of Kathmandu University whose guidance played an integral part in the completion of our project.

We would like to extend our thanks to Sr. Research Engineer Mr. Padam Prasad Pokharel and Laboratory Manager Mr. Yogesh Khadka, at Hydro Lab Pvt. Ltd., for their kind support in the testing of sediment samples for Particle Size Distribution (PSD) Analysis and Mineral Content Analysis. Their cooperation was indeed helpful for the success of the project.

We are very grateful to Er. Ramesh Tiwari and Mr. Purna Prasad Chauhan, Kulekhani – II Hydropower Plant for providing us Vibration Meter instrument which helped us in the vibration analysis.

At last, but not the least, we would like to thank our friends and family for the continuous support and encouragement.

Table of Contents

LIST OF ABBREVIATIONS. 11

CHAPTER ONE: INTRODUCTION.. 13

1.1 Background. 13

1.1.1 Energy Scenario of Nepal 15

1.1.2 Status of Alternative Energy in Nepal 16

1.1.3 Status of Hydropower in Nepal 17

1.2 Problem Statement 19

CHAPTER TWO: LITERATURE REVIEW... 24

2.1 Development of Hydropower Plant of Nepal 24

2.2 Classification. 25

2.2.1 ROR and Storage Plant 25

2.3 Types of Hydraulic Turbine. 26

2.3.1 Francis Turbine. 27

2.4 Main Problem in Hydropower Plants. 27

2.4.1 Sediment Erosion. 27

2.4.2 Cavitation. 29

2.4.2.1 Types of Cavitation. 29

2.4.2.2 Cavitation Damage Inspection. 31

2.4.2.3 Prevention of Cavitation. 32

2.4.3 Vibration. 33

CHAPTER THREE: CASE STUDY OF MMHP. 34

3.1 Introduction. 34

3.1.1 Salient Features of Middle Marsyangdi Hydropower Plant 35

3.1.2 Special Features of Middle Marsyangdi Hydropower Plant 38

3.2 Mechanical Components of MMHP. 39

3.2.1 Francis Turbine of MMHP. 39

3.2.2 Turbine Runner 41

CHAPTER FOUR: OBSERVATIONS, GRAPHS AND RESULTS. 44

4.1 Hydraulic Turbine (Main Dimensions) 44

4.2 Sediment Sample Testing. 45

4.2.1 Particle Size Distribution (PSD) Analysis. 46

4.2.2 Mineral Content Analysis. 46

4.2.3 Minerals in the Sediment Sample. 47

4.2.4 Result of Mineral Content Analysis. 48

4.3 Suction Velocity Measurement 49

4.3.1 Specifications of Digital Anemometer 49

4.4 Vibration Measurement 52

4.4.1Vibration Level Measurement 53

4.4.2 Portable Vibration Meter VM-62. 53

4.4.3 Measuring Range. 54

4.4.4 Graphs and Tables for Vibration. 54

4.4.4.1 Vibration in terms of Velocity (m/s) 55

4.4.5 Vibration in terms of Displacement (µm) 56

CHAPTER FIVE: MODELLING AND SIMULATION.. 60

5.1 Introduction. 60

5.2 Computational Fluid Dynamics Analysis: 60

5.3 Different terms used in simulation. 61

5.4 Reference geometry. 63

5.5 Simulation Results. 64

CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS. 67

6.1 Conclusion. 67

6.2 Recommendations. 68

REFERENCES. 69

APPENDIX A: SEDIMENT DATA OF MARSYANGDI RIVER.. 70

APPENDIX B: DATA OF VIBRATION OF MMHP. 72

APPENDIX C: LOG SCALE OF VIBRATION CONVERSION.. 75

APPENDIX D: VAPOUR PRESSURE CHART.. 76

APPENDIX E: SKETCH OF GUIDEVANE. 77

APPENDIX F: SKETCH OF TURBINE BLADE. 78

APPENDIX G: THREE VIEWS OF BLADE PROFILE. 79

APPENDIX H: SIMULATION RESULT OF VELOCITY.. 80

APPENDIX I: REPORTS OF SIMULATION.. 81

LIST OF TABLES

Table 1.1: Status of Alternative Energy in Nepal

Table 1.2: List of existing Hydropower Plants in Nepal

Table 1.3: List of Under Construction Medium and Large Hydropower Plants

Table 4.1: Hydraulic Turbine (Main Dimensions)

Table 4.2: Runner Dimension

Table 4.3: Wicket Gate Dimension

Table 4.4: Intake Sample

Table 4.5: Draft tube Sample

Table 4.6: Tail Race Sample

Table 4.7: Measurement Range

Table 4.8: Suction velocity and pressure at different power output

Table 4.9: Unit 1 at 34 MW (Full Load condition)

Table 4.10: Unit 1 at 23.1 MW (Part Load condition)

Table 4.11: Unit 1 at 23.1 MW (Part Load condition)

Table 4.12: Unit 1 at 23.1 MW (Part Load condition)

LIST OF FIGURES

Figure 1.1: Energy Consumption Scenario of Nepal, 2010

Figure 1.2: Electricity Generation and Consumption (MW/HR)

Figure 2.1: Power development map of Nepal

Figure 2.2: Francis Turbine (front view and top view)

Figure 2.3: Erosion in Guide vanes

Figure 2.4: Erosion in Turbine

Figure 2.5: Main types of cavitation in Francis turbines

Figure 3.1: Middle Marsyangdi Hydropower Scheme

Figure 3.2: Wicket gate blade

Figure 3.3: Guide vane and Stay ring

Figure 3.4: Francis Runner

Figure 3.5: Guide Bearing

Figure 4.1: Results of PSD Analysis

Figure 4.2: Anemometer

Figure 4.3: Suction Velocity Measurement at MMHP

Figure 4.4: Power vs. Suction Velocity

Figure 4.5: Power vs. Draft Tube Pressure

Figure 4.6: Vibration Measurements on Intermediate Shaft Cover using Vibration Meter

Figure 4.7: Position in Turbine vs. Velocity 34MW

Figure 4.8: Position in Turbine vs. Velocity 21.3MW

Figure 4.9: Frequency of Vibration in Unit 1

Figure 4.10: Frequency of Vibration in Unit 2

Figure 4.11: Displacement of Vibration in Unit 1

Figure 4.12: Displacement of Vibration in Unit 2

Figure 5.1: Reference Geometry of Blade and Guide vane

Figure 5.2: Reference Geometry of Runner with Guide vane

Figure 5.3: Velocity Profile at Full Load

Figure 5.4: Velocity Profile at Part Load

LIST OF ABBREVIATIONS

BKPC	Bhotekoshi Power Company
BPC	Butwal Power Company
CD	Cascade Desander
CES	Center for Energy Studies
CFD	Computational Fluid Dynamics
Ft/MIN	Feet per Minute
GWh	Giga Watt hour
HPL	Himal Power Limited
HPS	Hydro Power Station
IOE	Institute of Engineering
ISCR	Intermediate Shaft Cover Radial
ISCA KE	Intermediate Shaft Cover Axial Kinetic Energy
KU	Kathmandu University
KW	Kilo Watt
m ASL	meter Above Sea Level
MMHPS	Middle Marsyangdi Hydropower Station
MMHP		Middle Marsyangdi Hydropower Project
mm		millimeter
MoF		Ministry of Finance
MVA		Mega Volt Ampere
MW		Mega Watt
NEA		Nepal Electricity Authority
NHPC PE		Nepal Hydropower Company Potential Energy
PROR		Pondage Run-off-River
PSD		Particle Size Distribution
ROR		Run-Off-River
RPM		Revolution Per Minute
SERD		Sand Erosion Rate Density
TBHC		Turbine Bearing Head Cover
TOE		Tonnes Of Equivalent
U/L		Upper/Lower
IWM		Improved Water Mills

CHAPTER ONE

INTRODUCTION

1.1 Background

Nepal is blessed with immense amount of hydroelectric potential and is ranked second in terms of water resources after Brazil on global scale. Nepal is rich in natural resources. The most effective sector of all the resources is clean water and the concomitant electricity generated from its adequate water resources. Nepal is surrounded by mountainous hills having about 6000 rivers and small streams and rivulets. As most of the water flows through the densely populated southern region, the importance of hydroelectricity and clean water will be immense in the future. In the coming 10-30 years, the demand for clean water will increase considerably along with the tremendous increase in power demand (both at the domestic front and regional market).^[1]

Though Nepal has electricity generating potential of 83,000MW, about 43000MW power is seems to be economically and technically feasible. Hydropower is a big resource and leading sector for Nepal because of its adequate water potential (~225 billion cubic meter of water). Total installed capacity of electricity is 697 MW out of which energy from hydro is 644 MW and contribution by NEA is 477.53MW (including off-grid). Currently, power deficit of 400MW is prevalent in the country. Nepal’s electricity needs are mostly met by the hydropower generation. Despite the huge hydropower potential in Nepal, only 40% population has access to electricity; among them 33% get electricity from NEA and rest 7% from other alternative sources of energy like thermal plants, solar, bio-gas. According to 10^th plan, in 2010, only 42% of the present energy consumption was met by hydropower.

Hydropower is not only about energy production for productive sectors, but also powerful means of bringing in socio-economic transformation and development of villages. Hydropower leads to development activities in villages mostly as hydropower plants need to be constructed in the villages. The poor- the target group can benefit from this because the socio-economic benefit from a hydropower project to the rural populace is extensive.

In Nepal, the first hydropower was established in 1911 A.D., named Pharping (Chandrajoyti) Hydropower by Chandra Shamser with capacity of 500kW. Around 40 small-scale hydropower projects (between 100 kW and 10 MW) have been built in the Nepal. Except for a handful of these schemes (built in the 1990s and thereafter), the rest were built by Nepal Electricity Authority, (NEA), or its predecessor with financing from a number of bilateral and multilateral donors. Of the small hydropower plants, some are grid connected and others are isolated.

Unlike thermal and nuclear power plant, a hydropower project is very site specific particular site for the hydro power project will produce a specific amount of power and energy. The design and consequently the associated costs of hydropower project are very much dependent on the site.

Electricity crisis in Nepal is increasing day by day and many people are forced to live in dark night with low life standard. Micro hydro plant can only facilitate power to small village or a few number of houses, it cannot supply national wise. To overcome this problem development in large hydropower plant should be focused and utilization of water power risen. Various reasons are associated for less development of hydropower: their unfavorable topography, less industrial growth, limited network expansion, lack of adequate infrastructure, lack of skilled experts with the political instability. The development of hydropower plant is good option for using energy because of its minimal contribution to global warming, cleanliness, stability, more secure and environment friendly.

Several problems arise in the hydropower plants leading to the reduction in power output hence decreasing the efficiency of plant. In Nepal, hydropower suffers from the cavitation and erosion problem mainly, so our group decided to analyze the cause of this problem by taking Middle Marsyangdi Hydropower Plant as a case in final year project of Bachelor of Mechanical Engineering. MMHP is one of the major hydropower and has a special cavitation tube to reduce the cavitation effect which motivated us to select MMHP as the reference to analyze the cavitation and erosion problem.

1.1.1 Energy Scenario of Nepal

World average energy consumption per year per person is 68 Gigajoule. Per capita energy consumption of Nepal is 15 Gigajoule. Contribution of hydropower is only 1.82% while the petroleum products has share of 8% energy consumption in the Fiscal Year 2009/10 arose by 5.5 percent as compared to the Fiscal Year 2008/09 totaling 9,911 tons of oil equivalent (TOE). In the first eight months of current Fiscal Year 2010/11, energy consumption totaled 6,571 TOE. In the Fiscal Year 2009/10 the ratio of traditional, commercial, and renewable energy consumptions was 84.4 percent, 14.9 percent and 0.7 percent respectively. In the first eight months of fiscal year 2010/11 this ratio was recorded as 86.5 percent, 12.8 percent and 0.7 percent respectively. The data reveals that high dependence of Nepalese economy on traditional energy has not changed.

Traditional

87.89%

Petroleum

From all the existing power projects across the country, the total installed capacity (Including Private and Others) is 697.846 MW. Of the total electricity generated, 477.53MW (grid connected is 472.49MW and off grid is 4.536MW) has been generated from hydropower, NEA. Contribution from the thermal generation is about 53.4MW and that from the solar energy generated is 100KW. Total energy generated from hydropower in Nepal is 644.34MW.

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Figure 1.1: Energy consumption scenario of Nepal, 2010

(Source: Conference on Energy Efficiency and Renewal Energy, October 25-29, 2010, Islamabad, Pakistan)

In FY 2009/10, on a sector-wise basis, industries consumed 37.7 percent of electricity, while the households consumed 41.4 percent, business sector 7.2 percent, non-business sector 2.8 percent and miscellaneous sectors 10.9 percent. In FY 2010/11, industries are estimated to consume 37.44 percent of electricity, households 42.74 percent, business sector 7.7 percent and miscellaneous sectors 12.1 percent.

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Figure 1.2: Electricity Generation and Consumption (MW/HR)

1.1.2 Status of Alternative Energy in Nepal

A Rural Energy Fund has been set up under the AEPC to mobilise economic resources received from the Government of Nepal and donor agencies in a well-managed, simple and speedy way so as to invest in micro hydroelectricity projects, solar energy electricity system and improved bio-fuel system and to coordinate with banks to manage necessary credits. The establishment of the Fund has increased the access of rural citizens into new and sustainable energy systems, has taken ahead electrification process where national electricity transmission is not possible, has brought improvements in education and health and has directly contributed in income generation and employment. Likewise, to increase the access of low-income people to bio-gas (gobar gas), AEPC has been disbursing credits under the assistance of KfW (Forderung von Biogasanlagen) establishing a separate Bio-gas Credit Unit.^[2]

Table 1.1: Status of Alternative Energy in Nepal

RETS	Total installation		Unit	District Covered
RETS	Number	Capacity	Unit	District Covered
Hydropower(Micro, Pico, IWM)
Micro hydro	804	13.24	MW	59
Pico hydro	1274	2.45	MW	53
Improved Water Mills	6609			46
Biogas
Household biogas plant	217429			72
Institutional biogas plant	111			25
Community biogas Plant	61			20
Solar
Household Solar PV	192820	5.36	MW	74
Institutional Solar PV	259			42
Solar Pumping	79			26
Solar cooker/dryer	1408			30
Biomass
ICS	474922			48
Wind	19			11

1.1.3 Status of Hydropower in Nepal

Hydropower is one of the main sources of energy in Nepal. In the past 96 years, only 634MW of energy from the hydropower has been harnessed (NEA, 2009). Besides the total hydropower potential of Nepal stands at around 200000MW against the popularly assumed figure of 83000 MW. From more than 6000 rivers and rivulets of Nepal, around one million GWh of electricity can be generated. This potential is adequate enough to meet the total domestic and part of regional energy demands for many years. More importantly, there exists a robust potential of consuming this generated electricity for the next 3 decades.

The hydropower system in Nepal is dominated by run-off-river Projects. There is only one seasonal storage project in the system. There is shortage of power during winter and excess of power during wet season. The load factor is quite low as the majority of the consumption is dominated by household use. This imbalance has clearly shown the need for storage projects, and hence, cooperation between the two neighboring countries is essential for the best use of the hydro resource for mutual benefit. ^[3]

Table 1.2: List of existing Hydropower Plants in Nepal ^[4]

S.N.	Name	Installed	Type of	Facility of	Type of
	of Plants	Capacity(KW)	Turbine	De-silting basin	Plants
1	Pharping	500	Pelton	Small Water pond	ROR
2	Sundrijal	640	Pelton	Collecting Pond	ROR
3	Panauti	2400	Francis	Collecting Pond	ROR
4	Phewa	1088	Francis	Taal (as reservoir)	Canal drop
5	Trishuli	24000	Francis	Pond type	PROR
6	Sun Koshi	10050	Francis	Pond type	ROR
7	Tinau	1024	Francis	NA	ROR
8	Gandak	15000	Kaplan	Canal type	CD
9	Kulekhani-1	60000	Pelton	Reservoir	STORAGE
10	Devi Ghat	14100	Francis	Pond type	ROR
11	Seti	1500	Francis	Desander	CASCADE
12	Kulekhani-2	32000	Francis	Desander	CASCADE
13	Marsyangdi	69000	Francis	Pond type	PROR
14	Andhikhola	5100	Pelton	NA	ROR
15	Tatopani and Myagdi-I&II	2000	Francis	NA	ROR
16	Jhimruk	12500	Francis	Desander-S4	ROR
17	Puwa Khola	6200	Pelton	Desander	ROR
18	Khimti	60000	Pelton		ROR
19	Modi Khola	14800	Francis	Pond type	ROR
20	Chatara	3200	Bulb type		CD
21	Bhote Koshi	36000	Francis		ROR
22	Indrawati	7500	Francis		ROR
23	Kaligandaki	144000	Francis		PROR
24	Chilime	20000	Pelton		PROR
25	Small Sun –Koshi	2500	Turgo		ROR
26	Middle -Marsyangdi	70000	Francis		PROR

Table 1.3: List of Under Construction Medium and Large Hydropower Plants.

S.N.	Name of Plants	Installed Capacity(KW)	Type of Turbine	Type of Plants
1	Upper Tamakoshi	456000	Pelton	PROR
2	Chamelia	30000	Francis	PROR
3	Kulekhani-III	14000	Francis	CASCADE
4	Rahughat	30000	Francis	NA
5	Upper Seti	127000	Francis	STORAGE

1.2 Problem Statement

Air Admission system in MMHP is placed for the reduction of cavitation. It is in the testing phase and is of only kind in Nepal. Its effectiveness needs to be known and for that, the suction velocity can be measured against the power output. For these reasons the job of analysis of the role of the Air Admission System in preventing the cavitation.

Likewise, only the hand counted skilled persons are here in Nepal who works in CFD for the flow analysis and erosion in the mechanical components. So, till date almost no Hydropower Plants were found to opt for the simulation in prediction erosion in the mechanical components of turbine. Thus, the study of erosion in MMHP through modeling and simulation was undertaken.

1.3 Objectives

Main objective

· Analysis of Cavitation and Sediment Erosion in Francis Turbine of MMHP with Modelling and Simulation.

Specific objectives

· To observe the nature of the sediment particles present in water of MMHP.

· To study the effect of sediment particles in guide vane and runner of Francis turbine.

· To study the performance of Air Admission Tube.

· To perform software modelling of turbine parts in SOLIDWORKS.

· To perform simulation in ANSYS CFX.

1.4 Rationale

There are huge technical challenges to develop new hydropower projects involving risks of sediment erosion, especially the run-off-river ones. The declining performance of hydro turbines has become one of the major technical issues in the development of hydropower plants. Sediment transportation from the rivers is a natural phenomenon, it neither can be completely controlled, nor can be completely avoided; it should however be managed. Withdrawal of the clean water from the river for power production is expensive due to design, construction and operation of sediment settling basins. Even with the settling basins, 100% removal of fine sediments is impossible and uneconomical.

Different factors are needed to be considered for predicting the erosion. Therefore, dealing with sediment erosion problem requires a multidisciplinary approach. More research and development is needed to investigate the relationship between the particle movement and erosion inside a turbine and to establish the operating strategy for the turbine operating in sediment-laden water.

Extensive research has been done to develop a wear model in terms of the material properties involved but little attention has been given to clarify the influence of fluid motion, especially in the turbulent flow regime. In the context of Nepal there are rare cases of opting for the modeling and simulation for the clear understanding and visualization of the phenomenon, problems or conditions with prior acknowledgement of end results.

The cavitation phenomenon consists in formation and collapse of vapor bubbles in a fluid due to decreasing of local pressure under the equilibrium vapor pressure of water. The effects of cavitation are noise, vibrations and cavitation erosion of runner blades and adjacent areas. Cavitation erosion affects the components of mechanical systems which work in liquid environment. The biggest economic impact is found in hydraulic turbines, were runner blades and adjacent areas of the runner are submitted to cavitation.^[2]

Up to now the best results regarding repair techniques applied to turbine runner blades were obtained by overlay welding of cold hardening austenitic stainless steels. The main problems in case of repair welding in situ are connected to the residual stresses and to the important structural modifications of the base and filler materials, which appear during the welding process. These effects, especially when extensive welding is applied, can lead to the damage of the repaired component during following operation.

In case of Middle Marsyangdi Hydropower Plant, there is an Air Admission Tube which facilitates the suction of air from open air tube to the draft tube region of the turbine sets whenever the significant suction pressure prevails. This thereby results in the decrease in cavitation formation. As Middle Marsyangdi hydropower plant is the only plant in Nepal that incorporates Air Admission System, it is challenge as well as opportunity to study the cavitation reduction mechanism.

With enthusiasm of doing some kind of project in the field of hydropower, the case of MMHP was chosen to study cavitation and erosion phenomenon also to perform modeling and simulation to predict the critical regions of erosion in the turbine.

1.5 Methodology

The methodologies of this project are:

1. Literature review

· A detail study of the Middle Marsyangdi Hydropower Plant was made and the relevant data observation works were performed.

· The literature review of the relevant subject matters had been collected from websites, internet, course books and similar thesis reports.

2. Site visits

· Middle Marsyangdi Hydropower Plant was visited frequently and consulted with the mechanical engineers to get the relevant help regarding our project wok and to get the details about the mechanical components.

· Kathmandu University was visited for grasping the experts’ opinion regarding the project matters.

3. Data collection

· The sand samples were collected from the intake, draft tube and the tail race and was given to the Hydro Lab Pvt. Ltd. to observe the nature of particle reaching the turbine from the penstock.

· The air suction velocity at the Air Admission Tube and draft tube pressure were recorded with respect to variable power output. Instrument used for the velocity measurement was Digital Anemometer.

· The vibration of the mechanical components such as turbine casing and the draft tube were measured using an instrument named Vibration Meter.

4. Analysis

· Particle Size Distribution Analysis and Mineral Content Analysis were done in the Hydro Lab Pvt. Ltd.

· Suction velocity and draft tube pressure were correlated with the power output.

· Vibration measurement of different parts of the turbine unit was correlated with cavitation.

5. Modelling and Simulation

· Modelling of the Francis Turbine, Guide Vanes and the other turbine parts were done in SOLIDWORKS.

· Flow simulation was done using ANSYS CFX.

1.6 Limitations

Unavailability of the complete drawings of the runner and turbine parts.
The data at varying power generation was recorded only for two hours during day time.
The results of the software simulation may not solely be trustworthy.
The parameters such as inlet velocity and reference pressure were assumed for CFD analysis of the turbine.
Reverse-engineering process was adopted for measuring the dimension of runner, guide vane and blade profile.
Calibration of the Vibration Meter and Anemometer were not performed.

CHAPTER TWO

LITERATURE REVIEW

2.1 Development of Hydropower Plant of Nepal

Hydropower is environment friendly, clean source of renewable energy. World’s one- fifth electricity supply is fulfilled by the hydropower. The Pharping Hydropower Plant having capacity 500kW commissioned in 1911 is the first hydropower plant installed in Nepal and second in Asia. Then Sundarijal Hydropower Plant was commissioned in 1965 having capacity of 640kW.The 2.4MW Panauti Hydropower Plants was then installed. In 1982, Kulekhani I and II were commissioned having capacity of 60MW and 32 MW respectively. Kulekhani Hydropower Plant is the only plant offering seasonal water storage in Nepal. In 2003, the biggest hydropower in Nepal, Kaligandaki “A” Hydropower Plant with 144 MW was commissioned.

NEA (Nepal Electricity Authority) owned most of the hydropower while some of the hydropower projects in Nepal is designed, constructed and financed by the international consultant supported by the international assistant. Private hydropower developer also got involved in this sector after 1992. The companies are BPC (Butwal Power Company), HPL (Himal Power Limited), NHPC (Nepal Hydropower Company), BKPC (Bhotekoshi Power Company), Sanima Hydropower. Nepalese skilled expert are also getting involved in planning, designing and constructing hydropower like Chalice Hydropower Plants of 20 MW capacity. Upper Tamakoshi, Chamelia, Kulekhani III, Upper Seti Hydropower Project are under construction. ^[5]

Figure 2.1: Power development map of Nepal

2.2 Classification

Hydro power plants can be classified as based on head as low, medium and high head plants. Present categorization of hydropower according to power generated is:

Less than 1MW : Mini and micro hydro

1MW to 10 MW : Small hydro

10MW to 300MW : Medium hydro

Plants above 300MW : Big hydro

2.2.1 ROR and Storage Plant

Run-off-river plants depend on the discharge on the river, it has no more storage capacity. Diversion dam is constructed on the river to divert water and the water which exceeds the turbine capacity is spilled away. For ROR hydropower, head is up to 1000m. ROR plants with diversion type are best option to minimize the ecological impact. Most of the developed hydropower plants of Nepal are of ROR type. Because of the seasonal variation in the flow of river, there is excess power supply during the monsoon and load shedding in dry season.

In storage based hydropower project, the dam is built such that it creates large water storage capacity behind the dam to the river bed in the downstream portion, which is used to generate power. Kulekhani Hydropower Plant is a storage type and its only limitation is that it cannot fulfill the supply during dry season. There is now increasing trend of building ROR project than the storage type because in hilly region big gradient is available in short distance and no more area is needed like storage plants. MMHP is the run of river type with daily pondage of five hour peaking.

2.3 Types of Hydraulic Turbine

Turbine can be classified in various aspects. Based upon whether the pressure head available is fully or partially converted into the kinetic energy in the nozzle they are categorized into impulse and reaction turbines.

a) Impulse turbine

In this type, the available hydraulic energy is first converted into kinetic energy by means of an efficient nozzle. The velocity of jet is very high when coming from the nozzle. Then it strikes the suitably arranged bucket around the rim of wheel. The bucket changes the direction of the jet without changing its pressure. The motion of wheel and bucket change into rotary motion. It is then converted into mechanical energy which is available at the turbine shaft. When the fluid jet leaves the runner, then energy is reduced. Some impulse turbines are: Pelton Turbine, Girad Turbine, Banki Turbine and Jonval Turbine etc.

b) Reaction turbine

In this turbine only the portion of the fluid energy is transformed into kinetic energy before the fluid enters the turbine runner. A substantial part remains in the form of pressure energy. Subsequently both the velocity and pressure energy changes simultaneously as water glide along the turbine runner. The flow from inlet to outlet of the turbine is under pressure, and therefore, blades of a reaction turbine are closed, and passage is sealed from atmospheric conditions. Some important reaction turbines are: Fourneyron, Thomson, Francis, Kaplan and Propeller Turbine. Francis and Kaplan turbines are widely used at present.

2.3.1 Francis Turbine

In 1849 A.D. James B. Francis, an American Engineer, first developed an inward radial flow type of Reaction turbine. Later it was modified to modern Francis turbine, mixed flow type turbine. In Francis turbine water enters radially and leaves axially. It runs by the reaction force of the exiting fluid ^[6]. PE and KE of the fluid come to stationary part of Turbine and partly changes PE into KE. Moving part (runner) utilize both PE and KE. It works above atmospheric pressure and will be fully immersed in water. It has draft tube to use suction head thus increases the efficiency.

Figure 2.2: Francis Turbine (front view and top view)

Working

Water under pressure (from reservoir and penstock) enters the runner through guide vanes towards the center in radial direction and discharges out of the runner axially. Energy of water is transfer into the rotational energy of runner that rotates of shaft. There is a difference of pressure in between the guide vanes and the runner which is called reaction pressure and is responsible for the motion of the runner.

2.4 Main Problem in Hydropower Plants

2.4.1 Sediment Erosion

In water there is sand, silt, calcium oxide, quartz and various hard abrasive minerals which can erode the portion of turbine. Sediment erosion in the hydropower plant is the biggest problem and no one can ignore it. It is impossible to eliminate the sediment but we can somehow minimize it. So the extent of erosion of turbine and hydro machinery is also dependent on the size of particles. Sources of sediment are glacial deposits, land slide and intensively cultivated hill slopes. Desander or settling basin is used for sedimentation but complete removal of sediment particle do not occur and hence it passes through the penstock to the turbine and erode the blade of turbine , bush, draft tube cone, block the filter and damage the pipeline. Even small problems due to sediment may affect the efficiency of the power production and also the life of turbine and power efficiency.

The erosion of turbine component depends upon the

(i) Eroding particles - size, shape, hardness,

(ii) Substrates–chemistry, elastic properties, surface hardness, surface morphology, and (iii) Operating conditions – velocity, impingement angle, and concentration.

Figure 2.3: Erosion in Guide vanes

(Source: Mack R., P. Drtina, and E. Lang, 1999. Numerical prediction of erosion on guide vanes and in labyrinth seals in hydraulic turbines. Wear. 233 ‐ 235: 685 ‐ 691.)

Figure 2.4: Erosion in Francis Turbine

Depending on the gradient of the river and distance traversed by the sand particles, the shape and size of sediment particles vary at different locations of the same river system, whereas mineral content is dependent on the geological formation of the river course and its catchment area. ^[7]

2.4.2 Cavitation

Cavitation, which occurs in reaction water turbines, presents unwanted consequences such as flow instabilities, excessive vibrations, damage to material surfaces and degradation of machine performance. Cavitation is the condition when a liquid reaches a state at which vapour cavities are formed and grow due to dynamic-pressure reductions to the vapour pressure of the liquid at constant temperature. In a ﬂowing liquid, cavities are subjected to a pressure increase that stops and reverses their growth, collapsing implosively and eventually disappearing. The violent process of cavity collapse takes place in a very short time of about several nano seconds and resulting the emission of shock-waves, If the amplitude of the resulting pressure pulse is larger than the limit of the material mechanical strength, a hollow or indentation of several micrometers called ‘‘pit’’ will be formed on the surface. If an accumulation of pits take place in a narrow area, the material is ﬁnally eroded and mass loss occurs due to the repetitive action of the cavity collapsing. In a ﬂowing liquid, these cavities can take different forms that can be described as travelling bubbles, attached cavities or cavitating vortices.

Cavitation is the process that occurs in the draft tube, lower region of the turbine blades because pressure is decreased here. Thus the effect of cavitation is seen in these regions. The guide vanes and other upper parts of the turbine are unaffected by this damage.

2.4.2.1 Types of Cavitation

The main types of cavitation that can be induced in the Francis turbine are:

1. Leading edge cavitation

It takes the form of the attached cavity on the suction side of the runner blade due to operation at the high head than the machine design head when the incidence angle of the inlet flow is positive and largely deviated from the design value, it can also occur at the pressure side during operation at the lower head than the machine design head when the angle of incidence is zero. If unstable, this is a very aggressive type of cavitation that is likely to deeply erode the blades and to provoke pressure ﬂuctuations.

2. Travelling bubble cavitation

It takes the form of separated bubbles attached to the blade suction side near the mid-chord next to the trailing edge. These travelling bubbles appear due to low plant cavitation number and they grow with load reaching their maximum when the machine operates in overload condition with the highest ﬂow rate. This is a severe and noisy type of cavitation that reduces signiﬁcantly the machine efﬁciency and that can provoke erosion if the bubbles collapse on the blade.

3. Draft tube swirl

It is a cavitation vortex-core ﬂow that is formed just below the runner cone in the center of the draft tube. Its volume depends on the cavitation number and it appears at the partial load and over load. Due to the residual circumferential velocity component of the flow discharge from the runner, this vortex rotates in the same direction as the runner at part load and in opposite direction at the overload. From 50% up to 80% of the best efﬁciency flow rate, the vortex core takes a helical shape and presents a precession rotation at 0.25–0.35 times the runner rotating speed. In this case, circumferential pressure pulsations are generated at this low frequency. Strong ﬂuctuations may occur if the precession frequency matches one of the free natural oscillation frequencies of the draft tube or the penstock. This provokes the large bursts of the pressure pulses in the draft tube causing strong vibrations on the turbine and even on the power house. Beyond the best efﬁciency point the vortex is axially centered in the draft tube cone.

4. Inter blade vortex cavitation

This is formed by secondary vortices located in the channels between blades that arises due to the flow separation provoked by the incidence variation from the hub to the band. They can attach to the intersection of the blade inlet-edge with the crown or mid-way of the crown between the blades close to the suction side. Only if their tip is in touch with the runner surface they can result in erosion. These vortices appear in the partial load and resulting the high noise level. They can also appear and cavitate in extremely high head operation range because the cavitation number is relatively low and in this case they become unstable and cause strong vibration.

$Description: C:\Users\om jai jagdish\Desktop\c.PNG$

Figure 2.5: Main types of cavitation in Francis turbines: (1) leading edge cavitation,

(2) Travelling bubble cavitation, (3) draft tube swirl and (4) inter-blade vortex cavitation

Source: www.elsevier.com/locate/jnlabr/ymssp

2.4.2.2 Cavitation Damage Inspection

Periodic inspection of a turbine for cavitation damage is an important part of turbine maintenance. Frequent inspections are particularly important during the initial period for operation of a new turbine or new runner, as they will enable cavitation damage to be detected at an early stage and remedial measures to be effected before pitting becomes extensive. When a new turbine is placed into operation, the unit should be inspected after about 1500, 4000, and 8000 hours of operation. For pump-turbines, this frequency should be 750, 1500, and 3000 hours because of the potential for more severe cavitation pitting during pump operation. For this inspection, a hydraulic engineer from the turbine manufacturer should be present to inspect any areas of cavitation pitting and to report on the cause of the damage and possible remedial work to mitigate the damage. Subsequent to the initial inspection program, the frequency of future inspection should be dictated by the extent of damage which is occurring. "Cavitation damage inspection should be made from both the draft tube area below the runner and from the stay ring/wicket gate area in the spiral (or semi-spiral) case. Inspection from the draft tube area should normally be done from a temporary maintenance platform installed below the runner. Most areas of the runner which are susceptible to cavitation damage can be seen from the draft tube side. The leading edge of the blades, however, can best be inspected from the wicket gate area. On small units where access to the runner from the wicket gate area is poor, a polished metal mirror can be used for observing the leading edge area from the draft tube side.

For units which are experiencing minimum damage, the period between inspections can be increased. However, the frequency of inspection should not be less frequent than:

For Turbines . . . . . . . . . . . . . . . . . . Every 24,000 operating hours or every 4 years

For Pump-turbines . . . . . . . . . . . . . Every 12,000 operating hours or every 2 years

"Operating and maintenance experience, other than cavitation damage, may dictate a more frequent inspection (e.g., blade cracking, seal wear). Also, a more frequent inspection is warranted when making runner profile modifications so as to adequately monitor the effectiveness of the changes^.[8]

2.4.2.3 Prevention of Cavitation

To prevent cavitation from occurring altogether, a redesign of the turbine system would have to be undertaken where special consideration is given to the fluid pressure near the turbine runner. For this purpose the turbine runner should be designed such that the designed velocity at runner outlet will prevent pressure drop at this region. This is supported by the well-known Bernoulli’s equation which implies the inverse relationship between velocity and pressure. This prevents cavitation as there will be lower negative pressure. A significant decrease in fluid velocity will also decrease the efficiency of the turbine, and a compromise must be met. Ideally, the design should incorporate a tolerable amount of cavitation damage while minimizing the decrease to turbine efficiency.

2.4.3 Vibration

Vibration problems occur where there are rotating or moving parts in machinery. Apart from the machinery itself, the surrounding structure and human also face the vibration hazards because of the vibrating machinery. The effects of vibration are excessive stresses, undesirable noise, looseness of part and partial or complete failure of parts.

The draft tube is used to recuperate the kinetic energy downstream of the turbine runner. A well performing draft tube is therefore essential to achieve high efficiencies in hydroelectric power plant. However, at off-design operating conditions the fluid flow in the draft tube contains not only a through flow component equivalent to the discharge but also a swirl component. This type of flow can roll up to a vortex that rotates with a fraction of the rotational speed of the runner. Normally the rotational speed of the vortex lies between 30% and 50% of the runner speed. The corresponding pressure field rotates with the same speed leading to noise and vibration for the adjacent walls of the building.

Vibration on the external draft tube wall can be measured at several power levels to identify the power where the conditions are critical for the structure. Also, measurements can conducted at partial load with air injection from the middle of the turbine thru hollow shaft.

CHAPTER THREE

CASE STUDY OF MMHP

3.1 Introduction

The Middle Marsyangdi Hydro Electric Project (MMHEP) proposed for development by Nepal Electricity Authority (NEA) has a capacity of 70 MW and it generates annual average energy of 380 GWH. It is designed to meet the energy demand by utilizing the available Marsyangdi River flow and head without serious implications to the environment.

The MMHEP is located on the Marsyangdi River in Lamjung District of the Western Development Region of Nepal. The project site is accessed by Dumre–Besisahar single lane black-topped Feeder Road which connects district headquarters of Lamjung "Besisahar". The project site can be approached from Dumre situated at 130 km west from Kathmandu and 70 km east from Pokhara on Kathmandu-Pokhara National Highway (Prithibi Rajmarga). The Project site extends more than 10 km and is situated by the side of Dumre-Besisahar road at about 33 km north-east from Dumre Bazar.

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Figure 3.1: Middle Marshyangdi Hydropower Scheme

Source:(DYWIDAG International GmbH: A case study of MMHP)

3.1.1 Salient Features of Middle Marsyangdi Hydropower Plant

General

Type of project : Run of river with daily pondage for five hour peaking

Location : Phaila Sangu/Siudibar (Head works/Powerhouse)

Maximum gross head/net head (80m³/s) : 120/98m

Total length of the waterways : 5940m

Power & Energy

Installed capacity : 70 MW

Annual average energy : 398GWh

Hydrology

Catchments area : 2,729km²

Average annual flow : 99.5m³/s

Reservoir :

Minimum/Maximum operating levels : 621.0mASL/626.0masl

Live storage volume : 1.65 million m³

Surface area at maximum

operating level : 427,000m²(42.7 ha)

River diversion

Diversion flood : 560m³/s

Upstream cofferdam : Mass concrete dam, crest el.605.00masl

Downstream cofferdam : Earth- rock fill dam, crest el. 593.00 masl

Diversion Tunnel : Length 375.00m cross section

63.6m², concrete/shotcrete lined

Dam

Type of dam : Combined concrete gravity and rockfill dam

Crest el. Of dam : 629.00/630.00masl

Crest length of dam (in total) : 95m

Height above foundation : 34.50m (54min gorge)

Spillway capacity : 4,270m³s (Design flood, 10,000 years return period) at headwater level of 626.00 m ASL

Spillway gates3 : Radial gates, W x H =12.00x19.54m

Energy dissipation : Roller bucket

Intake Structures

Type : Submerged tunnel intakes with trash racks and gates.

Sill/Platform levels : 616.00 m ASL/629.00 m ASL

Length : 25m (intake structure) 70-75m Connecting tunnels to desanding basins)

Desanding basins

Type : Underground desander in caverns

Length/width/height per cavern : 130m/15m-27m

Number of basins : 6 accommodated in 3caverms, i. e. 2 in each

Length/width/height per basins : 100.75/7.50m/25.10m

Efficiency : 95%of particle size 0.2 mm max. sediment concentration 20,000 ppm

Flushing operation : Vertical flushing; BIERI system.

Operating levels (80m3/s) : Max.el.626.0mASL

Power Tunnel and Surge Tank

No. of adits : 5

Diameter : 5.4m

Power Tunnel (low pressure line)

Length : 5,230m (between desander outlet and surge tank)

Excavated tunnel diameter : 6.20m (branch tunnels=4.90m)

Lined tunnel diameter : 5.40m (branch tunnels=4.30m)

Lining : Concrete, partly reinforced

Surge tank

Type : Vertical, circular surge tank, underground, concrete lined with throttle

Net diameter : 20m, orifice Ø 2.90m

Height : 45m

Max. up- /down surge : El.640.93/ el.606.71 m ASL

Power tunnel (high pressure line)

Length : 225m (between surge tank and discharge measurement chamber)

Excavated tunnel diameter : 5.80m

Lined tunnel diameter : 4.60m

Lining : Steel

Penstock

Number, Type : 1, concrete cased steel pipe (cut and cover)

Diameter penstock/

bifurcation-manifold : Ø 4.60m / Ø3.00m to Ø2.40m

Length : 212-218m (between discharge measurement chamber and turbine inlet valve)

Powerhouse and Service Building

Type : Concrete structure below the ground constructed in an open excavation pit, 27m deep. Service building on top, above ground with bridge crane

Bridge Crane capacity : 130/10 tons

Tailrace length : 42.2m

Switchyard at MMHEP

Type : Open - air switchyard at el. 540.00 masl

Dimensions (L×W) : 43×50

Turbines

Number and Type : 2 Francis, vertical shaft

Rated discharge : 40 m3/s

Gross head : 110m

Rated output : 35.9 MW

Rated speed : 333.33 r.p.m.

Axis of scroll case : 515 m ASL

Generators

Number and Type : Two, 3-phase synchronous

Rated output : 39 MVA

Rated voltage : 11kv±7.5%

Rated frequency : 50Hz

Power factor : 0.85-0.90

Rated speed : 333.33 r.p.m(18 poles)

Fly wheel effect (GD2) : 600 tm²

Transmission line

Route : Middle Marsyangdi HPS-Lower Marsyangdi HPS

Nominal voltage/Length : 132 kV, 38.2 km [5]

3.1.2 Special Features of Middle Marsyangdi Hydropower Plant

1. Air Admission Tube (Cavitation tube)

2. Underground desander (Bieri type)

3. Soft coating on turbine blades

1. Air admission system: When water hits the turbine and it leaves then suddenly pressure changes from very high pressure to low pressure and causes the formation of bubble and it called as cavitation. So to balance the pressure, an Air Admission Tube is passed through the turbine to the draft tube portion and this tube is located in front of power house. When the pressure is below the atmospheric pressure then tube sucks the required air from the atmosphere and increases the pressure of the draft tube portion. Cavitation effect on the lower side of the runner, draft tube cone and draft tube portion. So this cavitation tube somewhat help to minimize this effect.

2. Underground desander: There are three underground desander and we can reach there from 500m long tunnel. Water enters from the trashrack and reach to the desander, each desander contains 8 parts, total is 24 parts and only one part operates at a time and deposited sand is remove from there from the flushing channel.

3. Soft coating in turbine blade: The base metal of turbine is stainless steel .Actually 2 coating is done in turbine that is primary and secondary coating. The special coating (soft coating) material is named as metalline 785 elastometic compound. It has rebounding properties and water does less effect in soft coating turbine than in hard coating turbine. It is applied to blade through the spray gun or brush.

3.2 Mechanical Components of MMHP

3.2.1 Francis Turbine of MMHP

The turbines of Middle Marsyangdi Hydropower Plant are of vertical shaft orientation fitted with the clockwise runner rotation, when viewed from the generator. On 333.33 rpm maximum power output of 39.9 MW can be achieved if the head water and tail water level are between 626 m ASL and 530 m ASL. The spiral case as well as the draft tube elbow is embedded in concrete. All static and dynamic forces resulting from weight, pressure, torque and thermal expansions are included into the foundation via upper and lower stay ring flanges.

The spiral inlet pipe has a thrust ring which transfers the axial forces directly into the concrete when the turbine inlet valve closed. The Turbine shaft line consists of Turbine main shaft and the intermediate shaft. The runner is coupled to the turbine shaft flange. The generator is coupled to the upper intermediate shaft flange. The guide bearing supported by the head cover and bearing cone, guide the lower shaft line. The thrust bearing is arranged below Generator.

The distributor is actuated by two servomotor anchored in the foundation through the operating ring links and levers, the position and angle of wicket gates are adjustable. The turbines and power house design allows disassembly of the turbine without dismantling the generator. The opening in concrete below spiral case allows dismantling of the bottom ring and draft tube cone from down.

Discharge ring

Stainless steel has a length of 1000mm and thickness of 30mm

Spiral casing

It is designed and constructed for a maximum operating pressure of 14 bars. The water from the penstock is conducted through the scroll casing and distributed completely around the circumference of the guide vane cascade.

The shape of casing helps to maintain the velocity of water high enough all around the runner Spiral casing shell is made from welded steel plates (material S355N) .it has manhole diameter 600m for inner inspection and maintenance.

Inlet pipe with thrust ring

Thrust ring will transmit the hydraulic force of the closed turbine inlet valve to the concrete structure and will ensure the exact position of the spiral casing, jointly with the pit liner under all operating condition.

Stay ring

It is a welded steel plate material of S355NZ35. It has three different shape with different stay vane angle.

Wicket gates

These vanes direct the water into the runner at an appropriate angle to the design. All the guide vanes are connected to a regulating ring. The governor through a rod rotates the ring to adjust the opening of the guide vane according to the load. The guide vanes have aerofoil shape which is shown in the picture. There are 24 wicket gates. They are machined cast material and supported by three bearings. They are designed to withhold the maximum dynamic pressure and vibration free operation. The gates are 60-65% opened. The soft coating on the gates protects from river abrasives substance.

Figure 3.2: Wicket gate blade

Figure 3.3: Guide vane and stay ring

Source: Middle Marsyangdi Hydropower Plant

3.2.2 Turbine Runner

It is the main unit of turbine in which high velocity water gives impulse and reactive effort to the blade due to which runner rotates with high rpm. In MMHP there are two Francis runners each of capacity 35MW. The runner is converts the pressure energy into mechanical energy. The power is thus developed in the shaft on which runner is mounted.

Runners are welded from casted parts: Crown, the runners installed in middle Marsyangdi are free from internal stress and casting imperfections. There are no hollows, depressions, waviness and projections. The runner blade inlet edges are hard coated while the surface are soft coated with metaline 785 elastomeric chemical. The chemical material is G-X5 Cr Ni 13 4.

The wearing ring at the crown side has the hardness of 300HB, and the chemical compound is X 3 Cr Ni 13 4. The hard coating thickness is 0.3mm.the total weight of runner and wearing ring is 5580kg.

Figure 3.4: Francis Runner

Shaft seal: It is located in the head cover and designed for easy inspection. It comprises the split seal, the rotating seal ring, stationary seal plate, remote wear indicator and a stainless steel shaft protecting sleeve. They are rust proof and wear/ tear resistant.

Guide bearing: The guide bearing is double segmented type with integrated oil tank mounted at the turbine shaft. The inner core has Babbit–metal lining of 3.5mm thick anchored firmly in two bearing segments. It is self-lubricating because of rotation of the lubricating oil tank with turbine shaft around the sliding segments. It is located at the head cover. It allows vertical movement of the runner and shaft for required adjustment and dismantling of thrust bearing and sufficient clearance between turbine and generator shaft. The guide bearing assures that no water can enter in lubrication system through leakage or condensation.

Description: SANY5132

Figure 3.5: Guide Bearing

Shaft: The shaft of MMHP is hollow type. It has a bore of 150mm in the centre for natural air admission system. The shaft material is forged metal of CK35 N. The shaft is divided as turbine shaft and intermediate shaft. The turbine shaft is the lowest part of main shaft and has the tolerances of 0.02mm. The intermediate shaft is between turbine shaft and generator shaft.

CHAPTER FOUR

OBSERVATIONS, GRAPHS AND RESULTS

4.1 Hydraulic Turbine (Main Dimensions)

Table 4.1: Hydraulic Turbine (Main Dimensions)

Spiral case inlet diameter	φ2600mm
Distributor apparatus pitch circular diameter	φ2462mm
No. of wicket gates	33.45degree φ145mm between gates
Wicket vane height	622.4mm
Runner inlet diameter	φ1786.9mm
Runner discharge diameter	φ2103.0mm
Runner height	1210.5mm
No. of blades	13
Turbine shaft with hollow bore	φ499.6mm h6/φ150mm (+2)
Intermediate shaft with hollow bore	φ500.0mm h6/ φ150mm (+2)
Turbine shaft range, upper/lower	φ900mm h9/φ920mm h9
Intermediate shaft flange U/L	φ900mm h9/ φ900mm h9
Turbine shaft length	1598mm
Intermediate shaft length	2158mm
Turbine guide bearing inner diameter	φ500mm H7

Runner Dimensions

Table 4.2 : Runner Dimensions

Type	f710/4(f599)
Material	G-X5CrNi134 (134=13% Cr, 4%Ni remaining stainless steel)
Diameter (mm)	2200
Z2(Number of Blade of runner)	13

Wicket Gates

Table 4.3 : Wicket Gates Dimensions

γ max(degree)	33.45
Zo(Number of wicket gates)	24
bo(height of wicket gate)	623 mm
Dz(Diameter of wicket gate)	246.2mm

4.2 Sediment Sample Testing

The sediment samples were collected from Intake Site, Draft Tube, and Tail Race of the Middle Marsyangdi Hydropower Plant as on 29 Ashad, 2068 and delivered to the Hydro Lab Pvt. Ltd. for the Particle Size Distribution (PSD) and Mineral Content Analysis.

4.2.1 Particle Size Distribution (PSD) Analysis.

The results of PSD analysis are given in the figure below:

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Source: Hydro Lab Pvt. Ltd.

Figure 4.1: Results of PSD Analysis

Above particle size distribution curve shows that the particle size at draft tube is decreased than that of intake. It signifies the effectiveness of desander. From particle size distribution analysis, we found that mainly the particles between 0.01mm and 1mm (large particles) are settled in desander. The diameter of particle at tailrace is slightly greater than that of draft tube. It may be due to mixing the sand from river.

4.2.2 Mineral Content Analysis

In order to carry out mineral content analysis, the sample was divided into three sets and analysed separately. Finally, the results of the three sets were averaged to have good representation of minerals.

4.2.3 Minerals in the Sediment Sample

Following are the minerals found in the sediment sample.

Quartz

Quartz is made up of a continuous framework of SiO4 silicon–oxygen tetrahedral, with each oxygen being shared between two tetrahedral, giving an overall formula SiO2.

Density: 2.65-2.66 gm/cm³

Feldspar

Feldspars (KAlSi₃O₈ – NaAlSi₃O₈ – CaAl₂Si₂O₈) are a group of rock-forming minerals which make up as much as 60% of the Earth's crust.

Density: 2.55 to 2.76 gm/cm³

Mica

Mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage.

Density: 1.60 gm/cm³

Tourmaline

Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of color

Density: 2.82 to 3.32 gm/cm³

Beryl

The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be₃Al₂(SiO₃)₆. Pure beryl is colorless.

Density: 3.1 to 4.3 gm/cm³

Carbonate

Density: 2 to 2.9 gm/cm³

4.2.4 Result of Mineral Content Analysis

Table 4.4: Intake Sample

Table 4.5: Draft tube Sample

Table 4.6: Tail Race Sample

Notes:

1. Others A: Tourmaline, Garnet and Beryl.

2. Others B: Carbonate (9%) and Clay.

Above tables show the concentration and hardness of sediment particles. Quartz is available in highest concentration, which has highest hardness. From this we conclude that the erosion is one of the major turbine damaging factors in MMHPP. So sediment is one of important parameter to be studied. At draft tube the concentration of quartz is decreased than that of intake but the concentration of mica is increased. It means that quartz is settled more than mica in desander. It may be due to the high density of quartz and low density of mica. Though mica is not settled effectively in desander, its effect is not significant because of low hardness of mica, the hardness value of feldspar is significant for erosion but its concentration is small. So its effect on erosion is not significant. Other particles (Tourmaline, Garnet, Beryl, Carbonate and clay) are in small concentration so their effect is also minimized. Mainly the quartz is responsible for erosion.

4.3 Suction Velocity Measurement

The suction velocity at the inlet of the Air Admission Tube was measured using an instrument named Digital Anemometer which was made available from Center Of Energy Studies (CES), Institute of Engineering, Pulchowk Campus.

An anemometer is a device for measuring wind speed. The term is derived from the Greek word anemos, meaning wind, and is used to describe any air speed measurement instrument used in meteorology or aerodynamics.

$Description: G:\Memories\gorkha tour\ashis\DSC05860.JPG$

4.3.1 Specifications of Digital Anemometer

(MODEL No. : AR826 by SMART SENSOR)

1) Features:

Wind speed measurement
Measuring unit options
Data hold
Max/Min/Avg measurement
LCD backlight
Auto power off

Figure 4.2: Anemometer

2) Operation Conditions:

Humidity: 40% to 85%

Temperature: 10^oC to 50^oC (14^oF to 122^oF)

3) Storage Conditions:

Humidity: 10% to 90%

Temperature: 20^oC to 60^oC (-4^oF to 140^oF)

4) Measurement Range

Table 4.7: Measurement Range

Unit	Range	Resolution	Threshold	Accuracy
m/s	0-45	0.1	0.3	±3%±0.1dgts
Ft/min	0-8800	19	60	±3%±10dgts
Knots	0-88	0.2	0.6	±3%±0.1dgts
Km/hr	0-140	0.3	1	±3%±0.1dgts
Mph	0-100	0.2	0.7	±3%±0.1dgts

5) Power Supply : 9V DC

Figure 4.3: Suction Velocity Measurement at MMHP

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Table 4.8: Suction velocity and pressure at different power output

Power(MW)	Suction Velocity(ft/min)	Spiral Casing Pressure(bar)	Draft tube pressure(bar)
20.08	3405	9.68	0.64
21	3661	9.65	0.64
22	3090	9.48	0.65
23.5	2913	9.69	0.65
25	2834	9.3	0.67
26.3	2248	9.42	0.69
26.9	1870	9.44	0.66
28	1791	9.56	0.69
29.2	1520	9.36	0.7
29.4	874	9.36	0.7
31.4	668	9.3	0.7
33	374	9.24	0.7
34	59	9.21	0.7
34.4	3	9.12	0.7

Graphs for Suction Velocity

The suction velocity of the Air Admission Tube of MMHP was recorded using Digital Anemometer and the following graphs and conclusions were observed.

Figure 4.4: Power vs. Suction Velocity

Above graph shows the relationship between suction velocity of Air Admission System and power output. The velocity and the power are inversely proportional. When the turbine runs in the full load i.e. producing 35MW then the suction velocity from the cavitation tube is near about zero. As the power generation decreased, the air suction velocity increased. At the varying power generation the draft tube pressure was recorded in similar manner, which is given below:

Figure 4.5: Power vs. Draft Tube Pressure

The above graph shows that at the full load condition pressure in the draft tube is more i.e. 0.7 bars. When the power is lowered, the pressure is not changed and draft tube parts and cause pitting. So to maintain the pressure on the draft tube portion suction velocity is more when the power is decreased. For example, when the power is 21 MW then suction velocities is about 3661 ft/min maintaining the pressure of 0.64 bars by flow pressure from atmospheric pressure to draft tube pressure.

4.4 Vibration Measurement

Currently, there is a trend to operate turbines in conditions far from their best efficiency point imposed by the variable demand on the energy market; therefore, it is important to determine the range of load where the turbine presents instability and seek ways of reducing this instability or adjusting the design so the structural elements can withstand the conditions at partial load. Air admission was an effective way to decrease pressure pulsation and wall stress. An air flow of certain % of the water discharge proved sufficient to improve the hydraulic stability.

Any increase in vibration level in machine or machine component in accordance with international/national standard gives an immediate indication of degradation of machine and occupational health exposure to workers. Vibration of the different mechanical components such as Regulating Ring, Turbine Bearing Head Cover, Intermediate Shaft Cover and Draft Tube were measured using Vibration Meter and the result was correlated to the cavitation.

4.4.1Vibration Level Measurement

Vibration level was recorded in both turbine units of MMHP at full load (power output 34MW) and partial load (power output 21.3MW) condition using vibration meter. Vibration Meter was held at a level for approximately 10 seconds to get a stable reading of RMS value of vibration data.

The reading was taken in four dimensional positions, 90 degree to each other in horizontal plane of each part, viz. regulating cover, turbine bearing head cover, intermediate shaft cover at radial position, intermediate shaft cover at axial position and draft tube.

4.4.2 Portable Vibration Meter VM-62

Portable Vibration Meter Model VM-62 is equipped with basic functions required to measure and evaluate wide range of machinery vibration. The used vibration pick up is a shear structure piezoelectric type with built-in preamplifier. This structure reduces cable noise and Pyro noise which cause error in small vibration measurements.

The vibration Pickup Model PV-57 assembled with the VM-62 converts the detected vibration into electric signal. As with this model vibration acceleration, velocity and displacement can be measured, we selected this vibration meter for the purpose of vibration measurement in the turbine casing and outer part of draft tube.

Figure 4.6 Vibration Measurement on Intermediate Shaft Cover using Vibration Meter

4.4.3 Measuring Range

The instrument had the following measuring range switch and frequency range:

Acceleration: 0.003~100 m/s², at 3Hz~5 KHz

Velocity: 0.03~100 cm/s, at 3Hz~5 KHz

Displacement: 0.03~10mm, at 10Hz~500Hz

The vibration measurement level in Acceleration unit was recorded by keeping the measurement range on m/s². Similarly, the vibration measurement levels in velocity units were recorded by keeping the measurement range on cm/s. The displacement measurement was out of range for the device. The acceleration and velocities both were calculated for RMS value.

4.4.4 Graphs and Tables for Vibration

With the help of Vibration Meter, the vibration of the different parts of the turbine unit (such as Regulating Ring, Turbine Bearing Head Cover, Intermediate Shaft (ISC) Covering Radial and ISC Axial) was measured after 10 seconds interval.

4.4.4.1 Vibration in terms of Velocity (m/s)

Figure 4.7 Positions in Turbine vs. Velocity 34MW

Figure 4.8 Positions in Turbine vs. Velocity 21.3MW

The velocity of vibration at different position of turbine at full load and part load is shown in above graphs. These graphs are plotted by using the data of vibration that was measured in terms of velocity (m/s) (see appendix F).

Excluding at intermediate shaft cover (ISC axial), overall pattern of vibration in unit one is more than that of unit two for the same power output. Being both turbines identical water borne vibration is identical. From this it is concluded that unit one has more structural vibration, which may be due to some fault during commissioning or other unknown reasons.

4.4.5 Vibration in terms of Displacement (µm)

The collected data of velocity and acceleration are used to find the frequency (Hz) and displacement (µm) from the log scale vibration chart (see appendix G). The frequency range of the vibration at any parts of the turbine of MMHP is within the safe range.

Table 4.9: Unit 1 at 34 MW (Full Load condition)

Table 4.10: Unit 1 at 23.1 MW (Part Load condition)

Table 4.11: Unit 2 at 34 MW (Part Load condition)

Table 4.12: Unit 2 at 23.1 MW (Part Load condition)

Figure 4.9: Frequency of Vibration in Unit 1

Figure 4.10: Frequency of Vibration in Unit 2

Figure 4.11: Displacement of Vibration in Unit 1

Figure 4.12: Displacement of Vibration in Unit 2

We know the violent process of cavity collapse takes place in a very short time of about several nano seconds. Partial load condition provides a low pressure condition in runner outlets. The guide vanes allow less water to flow into the runner. This creates obstruction to the flow of water, which causes water hammering thus leading to the vibration.

The above graph clearly shows that the displacement is decreased in every parts of the turbine, except in intermediate shaft cover, when the power output is lowered to 23.1 MW from 34MW. On the other hand, the frequency of the vibration has increased in the part load condition in both the turbine units, except for the frequencies at turbine head cover and intermediate shaft cover in axial position.

This decrease of displacement and increase of frequency at the part load indicates that the nature of vibration changes from low frequency-high amplitude to high frequency-low amplitude.

As there is change in nature of the vibration in partial load condition, with the lapse of time it further changes due to the increase in intensity of erosion added with the pitting effect of the cavitation. The increase in the frequency resembles more vigorous vibration. Whenever the frequency exceeds the allowable limit of the machine, maintenance of the turbine should be started. In the case of MMHP, the maximum frequency measured is 110Hz and it is well below the optimum range.

Thus it can be concluded that there is a clear effect of cavitation at part load. But there is no drastic increment in the frequency of vibration (not more than 60 Hz) at part load condition which is due to the Air Admission System that does not allow the pressure to drop below 0.26bar. It signifies the satisfactory performance of the Air Admission System in reducing the cavitation.

CHAPTER FIVE

MODELLING AND SIMULATION

5.1 Introduction

For the analysis of erosion, cavitation and vibration in turbine modelling and simulation become important tools and for this purpose we selected SOLIDWORKS for modelling and CFX for simulation. At first the turbine Model was created with the available data and with the input parameters of pressure 101.325 kpa, temperature 293.2k and turbine inlet velocity of 10m/s. with these references we obtained the simulated result for the pressure and velocity distribution in the turbine.

A model is a simplified representation of a system at some particular point in time or space intended to promote understanding of the real system and simulation is the manipulation of a model in such a way that it operates on time or space to compress it, thus enabling one to perceive the interactions that would not otherwise be apparent because of their separation in time or space.

Modeling and Simulation is a discipline for developing a level of understanding of the interaction of the parts of a system, and of the system as a whole. The level of understanding which may be developed via this discipline is seldom achievable via any other discipline.

A simulation generally refers to a computerized version of the model which is run over time to study the implications of the defined interactions. Simulations are generally iterative in there development. One develops a model, simulates it, learns from the simulation, revises the model, and continues the iterations until an adequate level of understanding is developed.

5.2 Computational Fluid Dynamics Analysis:

CFD is one of the tools for the simulation of fluid flow problems. It has various advantages like:

Low cost in designing phase
Less time consuming
More accurate than manual calculation for complex geometry like turbines

The main objectives of CFD analysis are as follows:

· To find out the critical region of erosion.

· To find out the best operating point in erosion point of view.

Computational Fluid Dynamics (CFD) Analysis is the analysis of systems involving fluid flow, heat transfer and related physical processes by means of computer based simulation. ANSYS CFX is general‐purpose CFD tool. It is a finite volume technique. In this technique, the region of interest is divided into small sub‐regions, called control volumes. The equations are discredited, and solved iteratively for each control volume. As a result, an approximation of the value of each variable at specific points throughout the domain can be obtained. From the result of individual control volume, the full picture of flow is obtained. It is a powerful CFD tool. It is capable of modeling: steady state and transient flows, laminar and turbulent flows, subsonic, transonic and supersonic flows, heat transfer and thermal radiation, buoyancy, non‐Newtonian flows, transport of non‐reacting scalar components, multiphase flows, combustion, flows in multiple frames of reference, particle tracking, etc. CFD analysis is a five step process, modeling, meshing, preprocessing, solving and post processing. Three softwares have been used to perform these tasks. SOLIDWORKS, for modeling, ICEMCFD for meshing and ANSYS CFX for analysis.^[9]

5.3 Different terms used in simulation:

A) Domain

The domain is the bounding volume within which CFD analysis is performed. CFX-Pre uses the concept of domains to define the type, properties and region of the fluid, porous or solid. Domains are regions of space in which the equations of fluid flow or heat transfer are solved. In our analysis we set up an environment that has water and sand defined one way. The sand properties are defined in material named sand.

B) General Erosion Model:

Erosion models are useful for design of turbine components, sediment settling basins and optimization of hydropower plant operation in sand laden-rivers .The wear of a wall due to the erosive effect of particle impacts is a complex function of particle impact, particle and wall properties. For nearly all metals, erosion is found to vary with impact angle and velocity according to the relationship.

The fundamental and simplest equation of erosion is:

Erosion = f (operating condition, properties of particles, properties of base material)

Generally this equation is given as a function velocity, material hardness, particle size, and concentration. Truscott on his literature survey of publications of 20 years on abrasive wear of hydraulic machinery has found that the most often quoted expression for Erosion ∞ (velocity).

Bardal describes the most general formula for pure erosion as:

W = K_mat. K_env.c. Vⁿ . f (α ) (mm/year)………………..eq.1

Here , W is erosion rate in mm/year, K_mat is material constant and K_env is constant depending on environment, c is concentration of particles and f(α) is function of impingement angle α. V is the velocity of particle and n is the exponent of velocity.^[10]

C) Boundary condition:

It is the condition of variables on the external boundaries. Boundaries are the points from where the solving process starts. Boundary conditions are applied in boundary region of domain and in domain interface. Boundary conditions can be inlets, outlets, openings, walls, and symmetry planes. In CFX, any unspecified boundary is named as default boundary and is a wall type boundary condition.

D) Inlet

The inlet boundary is the surface from where the fluid enters to the domain. We have used the normal velocity inlet boundary.

E) Outlet

The outlet boundary is the surface from where the fluid leaves the domain. We have used pressure outlet boundary.

F) Wall

The wall boundary is the water tight wall. It isolates the inner condition from the outer environment. All the restitution coefficients are defined in wall boundary.

5.4 Reference geometry

The reference geometry of turbine was made in solidworks. Image sketch feature of solidworks was used for modelling. Reverse engineering technique was used to sketch blade profile and guide vane(see appendix B). Further the model was meshed in ICEMCFD. This reference geometry is composed of 1,346,573 elements.

Figure 5.1: Reference Geometry of Blade and Guide Vane

Figure 5.2: Reference Geometry of Runner with Guide Vane

5.5 Simulation Results

As the manual iterative process for the static analysis of turbine is time consuming and less accurate, computer simulation is chosen. The simulation in ANSYS CFX is an iterative process that iterates the input data 100 times so as to give the best result.

The inputs for this process are velocity at inlet boundary and pressure at outlet boundary. The output of simulation is in the terms of velocity. It displays the velocity distribution in the domain.

The following are the velocity distribution profiles for full load and part load. These velocity distribution can be used to predict the erosion regions.

Figure 5.3: Velocity Profile at Full Load

Figure 5.4: Velocity Profile at Part Load

The above pictures are the top view of velocity profile of simulation result. The first profile belongs to velocity profile at full load and the second one is of part load condition. The velocity at the outlet of turbine blade is almost same for full load as well as part load. From the general model of erosion (equation no.1) the velocity gives significant effect on erosion rate. It shows that the erosion rate is almost same for full load and part load.

In case of guide vane, the velocity near the sealing region is increased at part load. It indicates that the erosion of guide vane increases, at part load.

CHAPTER SIX

CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

Erosion and cavitation are inevitable in Hydropower stations. Erosion rate and parts most affected can be predicated by sand sampling and simulation. Cavitation, on the other hand, can be controlled by increasing the pressure in low pressure region of reaction turbines by air admission system. If erosion and cavitation is controlled then the life of mechanical components increases as wear and tear is reduced. And under these conditions, efficiency of turbine increases. From our analysis, we come to the following conclusions:

1) The sediment has Quartz as the major constituent, 60% at intake and 51% at both the draft tube and tailrace, which is the hardest among the other mineral contents. Though 15% of the Quartz is settled in the desander its abrasive action in runner and guide vanes is very much significant.

2) The critical regions of erosion as indicated by simulation are sealing regions of guide vanes; and leading and trailing ends of runner blades.

3) The guide vanes are eroded with greater intensity at part load condition and the rate of erosion in runner blades is almost equal in full and partial load. Thus the best operating condition is full load condition.

4) Air suction maintains the draft tube pressure not lower than 0.64 bars at 21 MW, a part load condition the minimal range of increase of vibration frequency (60 Hz) at part load condition of turbine power output concludes the satisfactory effectiveness of the Air Admission System.

6.2 Recommendations

1. Erosion analysis by using appropriate erosion model is recommended.

2. The pressure variation at draft tube, compared with other hydropower station of similar capacity with no Air Admission System (Lower Marsyangdi Hydropower Plant) , would give better result.

3. Further research in evaluating the performance of desander is suggested.

4. It would be better to perform dynamic analysis of turbine model.

5. Noise measurement to relate it with the occurrence of cavitation is also recommended.

REFERENCES

· Dr. Jagadish Lal, Fluid Mechanics and Hydraulics, 10^th edition, published by Metropolitan Book Co. Pvt. Ltd.

Law, A. M., and W. D. Kelton. 1991. Simulation, Modeling and Analysis, second edition, Mc Graw-Hill
M. K. Natarajan, Principles of Fluid Mechanics Second Edition, OXFORD & IBH PUBLISHING CO. PVT.LTD.
R. K. RAJPUT, Textbook of Fluid Mechanics and Hydraulic Machines, S.CHAND AND COMPANY LTD., RAM NAGAR NEW DELHI-110055.
Thapa, Bhola, 2004.July,”Sand Erosion in Hydraulic Machinery”, MSc Thesis, Department of Mechanical Engineering
The license of ANSYS CFX software was used under the prior permission of Bim Prasad Shrestha, Head, Department of Mechanical Engineering, Kathmandu University.
Nepal Electricity Authority, A Year in Review – Fiscal Year 2009/10

[1] www.voithhydro.de/media/hypow_11_6.pdf

[2] www1.eere.energy.gov/industry/forest/pdfs/pulppaper_profile.pdf

[3] www.sari-energy.org/Publications/bbmalla.pdf

[4] Er. Suresh Raut, Final Year MSc Thesis, Department of Mechanical Engineering Tribhuvan University, Nepal.

[5] http://hydropower.inl.gov/turbines/pdfs/doeid-13741.pdf

[6] www.voithhydro.de/media/t3339e_Francis_72dpi.pdf

[7] www.tn.gov/environment/wpc/sed_ero_controlhandbook

[8] http://www.absoluteastronomy.com/topics/Cavitation

[9] http://www.featflow.de

[10]http://www.frenchriverland.com/cavitation_&_vibration_of_a_draft_tube [11]http://www.gtz.de/de/dokumente/en-divestment-of-nea-plants.pdf [12]http://www.hydroworld.com/index/display/article-display

[13]http//en.structurae.de/structure/data

[14]http://www.begellhouse.com/journals

[15]http://www.powervision-eng.ch/Profile/Publications/pdf/IAHR_2004.pdf

[16]http://acad-tim.tm.edu.ro/iSMART-flow/pdf/Muntean2_CIEM2009.pdf.

[17]http://jaibana.udea.edu.co/grupos/revista/revistas/.../Articulo%209.pdf

APPENDIX A: SEDIMENT DATA OF MARSYANGDI RIVER

Date	Reservoir water level	Intake (PPM)	De-sander (PPM)	Draft tube (PPM)	Gate opening( cm)			Remarks
Date	Reservoir water level	Intake (PPM)	De-sander (PPM)	Draft tube (PPM)	1	2	3	Remarks
7-Jul-10	622.35	3417			150
8-Jul-10	622.19	3279			160
9-Jul-10	622.28	3421			170
10-Jul-10	622.22	4889			235
11-Jul-10	622.19	5000			175
13-Jul-10	621.94	1122			125	50
14-Jul-10	622.03	1531					127
15-Jul-10	622.03	1692	1639	1475			133
17-Jul-10	622.98	5440	4615	2240		155		Highest ppm in draft tube
19-Jul-10	622.47	3469	2800	1818.2		145
21-Jul-10	622.14	1920	1718.8	1562.5			170
23-Jul-10	622.14	3556	960	937.5		171
25-Jul-10	622.03	3368	1111	1083.3	120	90
27-Jul-10	622.26	2558	2321	2667		200
29-Jul-10	621.98	2558	952	152		185
31-Jul-10	622.13	2609	1087	2459	90	140
2-Aug-10	622.03	2459	1522	667		150
4-Aug-10	621.77	1000	1087	682		180
6-Aug-10	622.23	2000	1304	1488		185
8-Aug-10	622.19	1538	1333	1000			140
10-Aug-10	622.04	971	591	434		125
12-Aug-10	622.16	581	434	321		145
14-Aug-10	622.13	824	696	786		130
16-Aug-10	621.97	2435	983	2210		1175		sand 57%silt 43%(intake)
18-Aug-10	622.13	2342	943	1787	100	100		sand 41%silt 59%(intake)
20-Aug-10	622.00	1002	754	1883	210			sand 48%silt 52%(intake)
22-Aug-10	622.08	1843	1676	735		252		sand 52.4%silt 47.6%(intake)
24-Aug-10	622.33	1647	734	719	155	73		sand 49.5%silt 50.5%(intake)
26-Aug-10	622.02	948	715	981	190			sand 47%silt 53%(intake)
28-Aug-10	622.13	2155	940	1609			220	sand 55%silt 45%(intake)
30-Aug-10	622.35	1827	961	1175	200	105		sand 49%silt 51%(intake)
1-Sep-10	622.1	2225	1372	1371	200	65		sand 65%silt 35%(intake)
3-Sep-10	622.03	2242	1537	167	210	55		sand 47%silt 53%(intake)
5-Sep-10	621.90	2009	671	65		250		sand 59%silt 41%(intake)
7-Sep-10	622.38	2374	717	651		210	119	sand 65%silt 35%(intake)
9-Sep-10	622.25	907	625	444		160		sand 58%silt 42%(intake)
11-Sep-10	622.40	717	338	491		165		sand 45%silt 55%(intake)
13-Sep-10	622.23	579	483	850		185		sand 51%silt 49%(intake)

APPENDIX B: DATA OF VIBRATION OF MMHP

Regulating Ring (Full Load Condition)

Turbine Bearing Head Cover (Full Load Condition)

Intermediate Shaft Cover Radial (Full Load Condition)

Intermediate Shaft Cover Axial (Full Load Condition)

Regulating Ring (Part Load Condition)

Turbine Bearing Head Cover (Part Load Condition)

Intermediate Shaft Cover radial (Part Load Condition)

Intermediate Shaft Cover axial (Part Load Condition)

Draft tube (Full Load Condition)

Draft tube (Part Load Condition)

APPENDIX C: LOG SCALE OF VIBRATION CONVERSION

Figure: Vibration criteria for machinery, sensitive equipment and human

(Source: Macinante, J.A., 1984)

APPENDIX D: VAPOUR PRESSURE CHART

APPENDIX E: SKETCH OF GUIDEVANE

All dimensions in mm	Part name	View
Scale 1:10	Guide vane	Top

APPENDIX F: SKETCH OF TURBINE BLADE

All dimensions in mm	Part name	View
Not to scale	Guide vane	Front

APPENDIX G: THREE VIEWS OF BLADE PROFILE

TOP VIEW

SIDE VIEW

FRONT VIEW

APPENDIX H: SIMULATION RESULT OF VELOCITY

Figure : Velocity profile of turbine of MMHP at full load (front view)

Figure : Velocity profile of turbine of MMHP at part load (front view)

APPENDIX I: REPORTS OF SIMULATION

Request for permission to copy or to make any other use of the material in this report in whole or in part should be addressed to:

Head

Department of Mechanical Engineering

Institute of Engineering, Pulchowk Campus

Lalitpur, Kathmandu

Nepal

TRIBHUVAN UNIVERSITY

INSTITUTE OF ENGINEERING

PULCHOWK CAMPUS

DEPARTMENT OF MECHANICAL ENGINEERING

Supervisor, Dr. Rajendra Shrestha

Head

Department of Mechanical Engineering

Tribhuvan University, Nepal

External Examiner, Er. Suresh Raut

Assistant Manager

Middle Marsyangdi Hydropower Plant, Lamjung

Committee Chairperson, Dr. Rajendra Shrestha

Head

Department of Mechanical Engineering

Date:

ABSTRACT

ACKNOWLEDGEMENT

We are very grateful to Er. Ramesh Tiwari and Mr. Purna Prasad Chauhan, Kulekhani – II Hydropower Plant for providing us Vibration Meter instrument which helped us in the vibration analysis.

At last, but not the least, we would like to thank our friends and family for the continuous support and encouragement.

Table of Contents

LIST OF ABBREVIATIONS. 11

CHAPTER ONE: INTRODUCTION.. 13

1.1 Background. 13

1.1.1 Energy Scenario of Nepal 15

1.1.2 Status of Alternative Energy in Nepal 16

1.1.3 Status of Hydropower in Nepal 17

1.2 Problem Statement 19

CHAPTER TWO: LITERATURE REVIEW... 24

2.1 Development of Hydropower Plant of Nepal 24

2.2 Classification. 25

2.2.1 ROR and Storage Plant 25

2.3 Types of Hydraulic Turbine. 26

2.3.1 Francis Turbine. 27

2.4 Main Problem in Hydropower Plants. 27

2.4.1 Sediment Erosion. 27

2.4.2 Cavitation. 29

2.4.2.1 Types of Cavitation. 29

2.4.2.2 Cavitation Damage Inspection. 31

2.4.2.3 Prevention of Cavitation. 32

2.4.3 Vibration. 33

CHAPTER THREE: CASE STUDY OF MMHP. 34

3.1 Introduction. 34

3.1.1 Salient Features of Middle Marsyangdi Hydropower Plant 35

3.1.2 Special Features of Middle Marsyangdi Hydropower Plant 38

3.2 Mechanical Components of MMHP. 39

3.2.1 Francis Turbine of MMHP. 39

3.2.2 Turbine Runner 41

CHAPTER FOUR: OBSERVATIONS, GRAPHS AND RESULTS. 44

4.1 Hydraulic Turbine (Main Dimensions) 44

4.2 Sediment Sample Testing. 45

4.2.1 Particle Size Distribution (PSD) Analysis. 46

4.2.2 Mineral Content Analysis. 46

4.2.3 Minerals in the Sediment Sample. 47

4.2.4 Result of Mineral Content Analysis. 48

4.3 Suction Velocity Measurement 49

4.3.1 Specifications of Digital Anemometer 49

4.4 Vibration Measurement 52

4.4.1Vibration Level Measurement 53

4.4.2 Portable Vibration Meter VM-62. 53

4.4.3 Measuring Range. 54

4.4.4 Graphs and Tables for Vibration. 54

4.4.4.1 Vibration in terms of Velocity (m/s) 55

4.4.5 Vibration in terms of Displacement (µm) 56

CHAPTER FIVE: MODELLING AND SIMULATION.. 60

5.1 Introduction. 60

5.2 Computational Fluid Dynamics Analysis: 60

5.3 Different terms used in simulation. 61

5.4 Reference geometry. 63

5.5 Simulation Results. 64

CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS. 67

6.1 Conclusion. 67

6.2 Recommendations. 68

REFERENCES. 69

APPENDIX A: SEDIMENT DATA OF MARSYANGDI RIVER.. 70

APPENDIX B: DATA OF VIBRATION OF MMHP. 72

APPENDIX C: LOG SCALE OF VIBRATION CONVERSION.. 75

APPENDIX D: VAPOUR PRESSURE CHART.. 76

APPENDIX E: SKETCH OF GUIDEVANE. 77

APPENDIX F: SKETCH OF TURBINE BLADE. 78

APPENDIX G: THREE VIEWS OF BLADE PROFILE. 79

APPENDIX H: SIMULATION RESULT OF VELOCITY.. 80

APPENDIX I: REPORTS OF SIMULATION.. 81

LIST OF TABLES

Table 1.1: Status of Alternative Energy in Nepal

Table 1.2: List of existing Hydropower Plants in Nepal

Table 1.3: List of Under Construction Medium and Large Hydropower Plants

Table 4.1: Hydraulic Turbine (Main Dimensions)

Table 4.2: Runner Dimension

Table 4.3: Wicket Gate Dimension

Table 4.4: Intake Sample

Table 4.5: Draft tube Sample

Table 4.6: Tail Race Sample

Table 4.7: Measurement Range

Table 4.8: Suction velocity and pressure at different power output

Table 4.9: Unit 1 at 34 MW (Full Load condition)

Table 4.10: Unit 1 at 23.1 MW (Part Load condition)

Table 4.11: Unit 1 at 23.1 MW (Part Load condition)

Table 4.12: Unit 1 at 23.1 MW (Part Load condition)

LIST OF FIGURES

Figure 1.1: Energy Consumption Scenario of Nepal, 2010

Figure 1.2: Electricity Generation and Consumption (MW/HR)

Figure 2.1: Power development map of Nepal

Figure 2.2: Francis Turbine (front view and top view)

Figure 2.3: Erosion in Guide vanes

Figure 2.4: Erosion in Turbine

Figure 2.5: Main types of cavitation in Francis turbines

Figure 3.1: Middle Marsyangdi Hydropower Scheme

Figure 3.2: Wicket gate blade

Figure 3.3: Guide vane and Stay ring

Figure 3.4: Francis Runner

Figure 3.5: Guide Bearing

Figure 4.1: Results of PSD Analysis

Figure 4.2: Anemometer

Figure 4.3: Suction Velocity Measurement at MMHP

Figure 4.4: Power vs. Suction Velocity

Figure 4.5: Power vs. Draft Tube Pressure

Figure 4.6: Vibration Measurements on Intermediate Shaft Cover using Vibration Meter

Figure 4.7: Position in Turbine vs. Velocity 34MW

Figure 4.8: Position in Turbine vs. Velocity 21.3MW

Figure 4.9: Frequency of Vibration in Unit 1

Figure 4.10: Frequency of Vibration in Unit 2

Figure 4.11: Displacement of Vibration in Unit 1

Figure 4.12: Displacement of Vibration in Unit 2

Figure 5.1: Reference Geometry of Blade and Guide vane

Figure 5.2: Reference Geometry of Runner with Guide vane

Figure 5.3: Velocity Profile at Full Load

Figure 5.4: Velocity Profile at Part Load

LIST OF ABBREVIATIONS

BKPC	Bhotekoshi Power Company
BPC	Butwal Power Company
CD	Cascade Desander
CES	Center for Energy Studies
CFD	Computational Fluid Dynamics
Ft/MIN	Feet per Minute
GWh	Giga Watt hour
HPL	Himal Power Limited
HPS	Hydro Power Station
IOE	Institute of Engineering
ISCR	Intermediate Shaft Cover Radial
ISCA KE	Intermediate Shaft Cover Axial Kinetic Energy
KU	Kathmandu University
KW	Kilo Watt
m ASL	meter Above Sea Level
MMHPS	Middle Marsyangdi Hydropower Station
MMHP		Middle Marsyangdi Hydropower Project
mm		millimeter
MoF		Ministry of Finance
MVA		Mega Volt Ampere
MW		Mega Watt
NEA		Nepal Electricity Authority
NHPC PE		Nepal Hydropower Company Potential Energy
PROR		Pondage Run-off-River
PSD		Particle Size Distribution
ROR		Run-Off-River
RPM		Revolution Per Minute
SERD		Sand Erosion Rate Density
TBHC		Turbine Bearing Head Cover
TOE		Tonnes Of Equivalent
U/L		Upper/Lower
IWM		Improved Water Mills

CHAPTER ONE

INTRODUCTION

1.1 Background

1.1.1 Energy Scenario of Nepal

Traditional

87.89%

Petroleum

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Figure 1.1: Energy consumption scenario of Nepal, 2010

(Source: Conference on Energy Efficiency and Renewal Energy, October 25-29, 2010, Islamabad, Pakistan)

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Figure 1.2: Electricity Generation and Consumption (MW/HR)

1.1.2 Status of Alternative Energy in Nepal

Table 1.1: Status of Alternative Energy in Nepal

RETS	Total installation		Unit	District Covered
RETS	Number	Capacity	Unit	District Covered
Hydropower(Micro, Pico, IWM)
Micro hydro	804	13.24	MW	59
Pico hydro	1274	2.45	MW	53
Improved Water Mills	6609			46
Biogas
Household biogas plant	217429			72
Institutional biogas plant	111			25
Community biogas Plant	61			20
Solar
Household Solar PV	192820	5.36	MW	74
Institutional Solar PV	259			42
Solar Pumping	79			26
Solar cooker/dryer	1408			30
Biomass
ICS	474922			48
Wind	19			11

1.1.3 Status of Hydropower in Nepal

Table 1.2: List of existing Hydropower Plants in Nepal ^[4]

S.N.	Name	Installed	Type of	Facility of	Type of
	of Plants	Capacity(KW)	Turbine	De-silting basin	Plants
1	Pharping	500	Pelton	Small Water pond	ROR
2	Sundrijal	640	Pelton	Collecting Pond	ROR
3	Panauti	2400	Francis	Collecting Pond	ROR
4	Phewa	1088	Francis	Taal (as reservoir)	Canal drop
5	Trishuli	24000	Francis	Pond type	PROR
6	Sun Koshi	10050	Francis	Pond type	ROR
7	Tinau	1024	Francis	NA	ROR
8	Gandak	15000	Kaplan	Canal type	CD
9	Kulekhani-1	60000	Pelton	Reservoir	STORAGE
10	Devi Ghat	14100	Francis	Pond type	ROR
11	Seti	1500	Francis	Desander	CASCADE
12	Kulekhani-2	32000	Francis	Desander	CASCADE
13	Marsyangdi	69000	Francis	Pond type	PROR
14	Andhikhola	5100	Pelton	NA	ROR
15	Tatopani and Myagdi-I&II	2000	Francis	NA	ROR
16	Jhimruk	12500	Francis	Desander-S4	ROR
17	Puwa Khola	6200	Pelton	Desander	ROR
18	Khimti	60000	Pelton		ROR
19	Modi Khola	14800	Francis	Pond type	ROR
20	Chatara	3200	Bulb type		CD
21	Bhote Koshi	36000	Francis		ROR
22	Indrawati	7500	Francis		ROR
23	Kaligandaki	144000	Francis		PROR
24	Chilime	20000	Pelton		PROR
25	Small Sun –Koshi	2500	Turgo		ROR
26	Middle -Marsyangdi	70000	Francis		PROR

Table 1.3: List of Under Construction Medium and Large Hydropower Plants.

S.N.	Name of Plants	Installed Capacity(KW)	Type of Turbine	Type of Plants
1	Upper Tamakoshi	456000	Pelton	PROR
2	Chamelia	30000	Francis	PROR
3	Kulekhani-III	14000	Francis	CASCADE
4	Rahughat	30000	Francis	NA
5	Upper Seti	127000	Francis	STORAGE

1.2 Problem Statement

1.3 Objectives

Main objective

· Analysis of Cavitation and Sediment Erosion in Francis Turbine of MMHP with Modelling and Simulation.

Specific objectives

· To observe the nature of the sediment particles present in water of MMHP.

· To study the effect of sediment particles in guide vane and runner of Francis turbine.

· To study the performance of Air Admission Tube.

· To perform software modelling of turbine parts in SOLIDWORKS.

· To perform simulation in ANSYS CFX.

1.4 Rationale

1.5 Methodology

The methodologies of this project are:

1. Literature review

· A detail study of the Middle Marsyangdi Hydropower Plant was made and the relevant data observation works were performed.

· The literature review of the relevant subject matters had been collected from websites, internet, course books and similar thesis reports.

2. Site visits

· Kathmandu University was visited for grasping the experts’ opinion regarding the project matters.

3. Data collection

· The sand samples were collected from the intake, draft tube and the tail race and was given to the Hydro Lab Pvt. Ltd. to observe the nature of particle reaching the turbine from the penstock.

· The vibration of the mechanical components such as turbine casing and the draft tube were measured using an instrument named Vibration Meter.

4. Analysis

· Particle Size Distribution Analysis and Mineral Content Analysis were done in the Hydro Lab Pvt. Ltd.

· Suction velocity and draft tube pressure were correlated with the power output.

· Vibration measurement of different parts of the turbine unit was correlated with cavitation.

5. Modelling and Simulation

· Modelling of the Francis Turbine, Guide Vanes and the other turbine parts were done in SOLIDWORKS.

· Flow simulation was done using ANSYS CFX.

1.6 Limitations

Unavailability of the complete drawings of the runner and turbine parts.
The data at varying power generation was recorded only for two hours during day time.
The results of the software simulation may not solely be trustworthy.
The parameters such as inlet velocity and reference pressure were assumed for CFD analysis of the turbine.
Reverse-engineering process was adopted for measuring the dimension of runner, guide vane and blade profile.
Calibration of the Vibration Meter and Anemometer were not performed.

CHAPTER TWO

LITERATURE REVIEW

2.1 Development of Hydropower Plant of Nepal

Figure 2.1: Power development map of Nepal

2.2 Classification

Hydro power plants can be classified as based on head as low, medium and high head plants. Present categorization of hydropower according to power generated is:

Less than 1MW : Mini and micro hydro

1MW to 10 MW : Small hydro

10MW to 300MW : Medium hydro

Plants above 300MW : Big hydro

2.2.1 ROR and Storage Plant

2.3 Types of Hydraulic Turbine

a) Impulse turbine

b) Reaction turbine

2.3.1 Francis Turbine

Figure 2.2: Francis Turbine (front view and top view)

Working

2.4 Main Problem in Hydropower Plants

2.4.1 Sediment Erosion

The erosion of turbine component depends upon the

(i) Eroding particles - size, shape, hardness,

(ii) Substrates–chemistry, elastic properties, surface hardness, surface morphology, and (iii) Operating conditions – velocity, impingement angle, and concentration.

Figure 2.3: Erosion in Guide vanes

(Source: Mack R., P. Drtina, and E. Lang, 1999. Numerical prediction of erosion on guide vanes and in labyrinth seals in hydraulic turbines. Wear. 233 ‐ 235: 685 ‐ 691.)

Figure 2.4: Erosion in Francis Turbine

2.4.2 Cavitation

2.4.2.1 Types of Cavitation

The main types of cavitation that can be induced in the Francis turbine are:

1. Leading edge cavitation

2. Travelling bubble cavitation

3. Draft tube swirl

4. Inter blade vortex cavitation

$Description: C:\Users\om jai jagdish\Desktop\c.PNG$

Figure 2.5: Main types of cavitation in Francis turbines: (1) leading edge cavitation,

(2) Travelling bubble cavitation, (3) draft tube swirl and (4) inter-blade vortex cavitation

Source: www.elsevier.com/locate/jnlabr/ymssp

2.4.2.2 Cavitation Damage Inspection

For units which are experiencing minimum damage, the period between inspections can be increased. However, the frequency of inspection should not be less frequent than:

For Turbines . . . . . . . . . . . . . . . . . . Every 24,000 operating hours or every 4 years

For Pump-turbines . . . . . . . . . . . . . Every 12,000 operating hours or every 2 years

2.4.2.3 Prevention of Cavitation

2.4.3 Vibration

CHAPTER THREE

CASE STUDY OF MMHP

3.1 Introduction

$Description: C:\Users\om jai jagdish\Desktop\Capture.JPG$

Figure 3.1: Middle Marshyangdi Hydropower Scheme

Source:(DYWIDAG International GmbH: A case study of MMHP)

3.1.1 Salient Features of Middle Marsyangdi Hydropower Plant

General

Type of project : Run of river with daily pondage for five hour peaking

Location : Phaila Sangu/Siudibar (Head works/Powerhouse)

Maximum gross head/net head (80m³/s) : 120/98m

Total length of the waterways : 5940m

Power & Energy

Installed capacity : 70 MW

Annual average energy : 398GWh

Hydrology

Catchments area : 2,729km²

Average annual flow : 99.5m³/s

Reservoir :

Minimum/Maximum operating levels : 621.0mASL/626.0masl

Live storage volume : 1.65 million m³

Surface area at maximum

operating level : 427,000m²(42.7 ha)

River diversion

Diversion flood : 560m³/s

Upstream cofferdam : Mass concrete dam, crest el.605.00masl

Downstream cofferdam : Earth- rock fill dam, crest el. 593.00 masl

Diversion Tunnel : Length 375.00m cross section

63.6m², concrete/shotcrete lined

Dam

Type of dam : Combined concrete gravity and rockfill dam

Crest el. Of dam : 629.00/630.00masl

Crest length of dam (in total) : 95m

Height above foundation : 34.50m (54min gorge)

Spillway capacity : 4,270m³s (Design flood, 10,000 years return period) at headwater level of 626.00 m ASL

Spillway gates3 : Radial gates, W x H =12.00x19.54m

Energy dissipation : Roller bucket

Intake Structures

Type : Submerged tunnel intakes with trash racks and gates.

Sill/Platform levels : 616.00 m ASL/629.00 m ASL

Length : 25m (intake structure) 70-75m Connecting tunnels to desanding basins)

Desanding basins

Type : Underground desander in caverns

Length/width/height per cavern : 130m/15m-27m

Number of basins : 6 accommodated in 3caverms, i. e. 2 in each

Length/width/height per basins : 100.75/7.50m/25.10m

Efficiency : 95%of particle size 0.2 mm max. sediment concentration 20,000 ppm

Flushing operation : Vertical flushing; BIERI system.

Operating levels (80m3/s) : Max.el.626.0mASL

Power Tunnel and Surge Tank

No. of adits : 5

Diameter : 5.4m

Power Tunnel (low pressure line)

Length : 5,230m (between desander outlet and surge tank)

Excavated tunnel diameter : 6.20m (branch tunnels=4.90m)

Lined tunnel diameter : 5.40m (branch tunnels=4.30m)

Lining : Concrete, partly reinforced

Surge tank

Type : Vertical, circular surge tank, underground, concrete lined with throttle

Net diameter : 20m, orifice Ø 2.90m

Height : 45m

Max. up- /down surge : El.640.93/ el.606.71 m ASL

Power tunnel (high pressure line)

Length : 225m (between surge tank and discharge measurement chamber)

Excavated tunnel diameter : 5.80m

Lined tunnel diameter : 4.60m

Lining : Steel

Penstock

Number, Type : 1, concrete cased steel pipe (cut and cover)

Diameter penstock/

bifurcation-manifold : Ø 4.60m / Ø3.00m to Ø2.40m

Length : 212-218m (between discharge measurement chamber and turbine inlet valve)

Powerhouse and Service Building

Type : Concrete structure below the ground constructed in an open excavation pit, 27m deep. Service building on top, above ground with bridge crane

Bridge Crane capacity : 130/10 tons

Tailrace length : 42.2m

Switchyard at MMHEP

Type : Open - air switchyard at el. 540.00 masl

Dimensions (L×W) : 43×50

Turbines

Number and Type : 2 Francis, vertical shaft

Rated discharge : 40 m3/s

Gross head : 110m

Rated output : 35.9 MW

Rated speed : 333.33 r.p.m.

Axis of scroll case : 515 m ASL

Generators

Number and Type : Two, 3-phase synchronous

Rated output : 39 MVA

Rated voltage : 11kv±7.5%

Rated frequency : 50Hz

Power factor : 0.85-0.90

Rated speed : 333.33 r.p.m(18 poles)

Fly wheel effect (GD2) : 600 tm²

Transmission line

Route : Middle Marsyangdi HPS-Lower Marsyangdi HPS

Nominal voltage/Length : 132 kV, 38.2 km [5]

3.1.2 Special Features of Middle Marsyangdi Hydropower Plant

1. Air Admission Tube (Cavitation tube)

2. Underground desander (Bieri type)

3. Soft coating on turbine blades

3.2 Mechanical Components of MMHP

3.2.1 Francis Turbine of MMHP

Discharge ring

Stainless steel has a length of 1000mm and thickness of 30mm

Spiral casing

Inlet pipe with thrust ring

Stay ring

It is a welded steel plate material of S355NZ35. It has three different shape with different stay vane angle.

Wicket gates

Figure 3.2: Wicket gate blade

Figure 3.3: Guide vane and stay ring

Source: Middle Marsyangdi Hydropower Plant

3.2.2 Turbine Runner

The wearing ring at the crown side has the hardness of 300HB, and the chemical compound is X 3 Cr Ni 13 4. The hard coating thickness is 0.3mm.the total weight of runner and wearing ring is 5580kg.

Figure 3.4: Francis Runner

Description: SANY5132

Figure 3.5: Guide Bearing

CHAPTER FOUR

OBSERVATIONS, GRAPHS AND RESULTS

4.1 Hydraulic Turbine (Main Dimensions)

Table 4.1: Hydraulic Turbine (Main Dimensions)

Spiral case inlet diameter	φ2600mm
Distributor apparatus pitch circular diameter	φ2462mm
No. of wicket gates	33.45degree φ145mm between gates
Wicket vane height	622.4mm
Runner inlet diameter	φ1786.9mm
Runner discharge diameter	φ2103.0mm
Runner height	1210.5mm
No. of blades	13
Turbine shaft with hollow bore	φ499.6mm h6/φ150mm (+2)
Intermediate shaft with hollow bore	φ500.0mm h6/ φ150mm (+2)
Turbine shaft range, upper/lower	φ900mm h9/φ920mm h9
Intermediate shaft flange U/L	φ900mm h9/ φ900mm h9
Turbine shaft length	1598mm
Intermediate shaft length	2158mm
Turbine guide bearing inner diameter	φ500mm H7

Runner Dimensions

Table 4.2 : Runner Dimensions

Type	f710/4(f599)
Material	G-X5CrNi134 (134=13% Cr, 4%Ni remaining stainless steel)
Diameter (mm)	2200
Z2(Number of Blade of runner)	13

Wicket Gates

Table 4.3 : Wicket Gates Dimensions

γ max(degree)	33.45
Zo(Number of wicket gates)	24
bo(height of wicket gate)	623 mm
Dz(Diameter of wicket gate)	246.2mm

4.2 Sediment Sample Testing

4.2.1 Particle Size Distribution (PSD) Analysis.

The results of PSD analysis are given in the figure below:

$Description: C:\Users\om jai jagdish\Desktop\Capture.JPG$

Source: Hydro Lab Pvt. Ltd.

Figure 4.1: Results of PSD Analysis

4.2.2 Mineral Content Analysis

4.2.3 Minerals in the Sediment Sample

Following are the minerals found in the sediment sample.

Quartz

Quartz is made up of a continuous framework of SiO4 silicon–oxygen tetrahedral, with each oxygen being shared between two tetrahedral, giving an overall formula SiO2.

Density: 2.65-2.66 gm/cm³

Feldspar

Feldspars (KAlSi₃O₈ – NaAlSi₃O₈ – CaAl₂Si₂O₈) are a group of rock-forming minerals which make up as much as 60% of the Earth's crust.

Density: 2.55 to 2.76 gm/cm³

Mica

Mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage.

Density: 1.60 gm/cm³

Tourmaline

Density: 2.82 to 3.32 gm/cm³

Beryl

The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be₃Al₂(SiO₃)₆. Pure beryl is colorless.

Density: 3.1 to 4.3 gm/cm³

Carbonate

Density: 2 to 2.9 gm/cm³

4.2.4 Result of Mineral Content Analysis

Table 4.4: Intake Sample

Table 4.5: Draft tube Sample

Table 4.6: Tail Race Sample

Notes:

1. Others A: Tourmaline, Garnet and Beryl.

2. Others B: Carbonate (9%) and Clay.

4.3 Suction Velocity Measurement

$Description: G:\Memories\gorkha tour\ashis\DSC05860.JPG$

4.3.1 Specifications of Digital Anemometer

(MODEL No. : AR826 by SMART SENSOR)

1) Features:

Wind speed measurement
Measuring unit options
Data hold
Max/Min/Avg measurement
LCD backlight
Auto power off

Figure 4.2: Anemometer

2) Operation Conditions:

Humidity: 40% to 85%

Temperature: 10^oC to 50^oC (14^oF to 122^oF)

3) Storage Conditions:

Humidity: 10% to 90%

Temperature: 20^oC to 60^oC (-4^oF to 140^oF)

4) Measurement Range

Table 4.7: Measurement Range

Unit	Range	Resolution	Threshold	Accuracy
m/s	0-45	0.1	0.3	±3%±0.1dgts
Ft/min	0-8800	19	60	±3%±10dgts
Knots	0-88	0.2	0.6	±3%±0.1dgts
Km/hr	0-140	0.3	1	±3%±0.1dgts
Mph	0-100	0.2	0.7	±3%±0.1dgts

5) Power Supply : 9V DC

Figure 4.3: Suction Velocity Measurement at MMHP

$Description: G:\Memories\gorkha tour\ashis\DSC05859.JPG$

Table 4.8: Suction velocity and pressure at different power output

Power(MW)	Suction Velocity(ft/min)	Spiral Casing Pressure(bar)	Draft tube pressure(bar)
20.08	3405	9.68	0.64
21	3661	9.65	0.64
22	3090	9.48	0.65
23.5	2913	9.69	0.65
25	2834	9.3	0.67
26.3	2248	9.42	0.69
26.9	1870	9.44	0.66
28	1791	9.56	0.69
29.2	1520	9.36	0.7
29.4	874	9.36	0.7
31.4	668	9.3	0.7
33	374	9.24	0.7
34	59	9.21	0.7
34.4	3	9.12	0.7

Graphs for Suction Velocity

The suction velocity of the Air Admission Tube of MMHP was recorded using Digital Anemometer and the following graphs and conclusions were observed.

Figure 4.4: Power vs. Suction Velocity

Figure 4.5: Power vs. Draft Tube Pressure

4.4 Vibration Measurement

4.4.1Vibration Level Measurement

4.4.2 Portable Vibration Meter VM-62

Figure 4.6 Vibration Measurement on Intermediate Shaft Cover using Vibration Meter

4.4.3 Measuring Range

The instrument had the following measuring range switch and frequency range:

Acceleration: 0.003~100 m/s², at 3Hz~5 KHz

Velocity: 0.03~100 cm/s, at 3Hz~5 KHz

Displacement: 0.03~10mm, at 10Hz~500Hz

4.4.4 Graphs and Tables for Vibration

4.4.4.1 Vibration in terms of Velocity (m/s)

Figure 4.7 Positions in Turbine vs. Velocity 34MW

Figure 4.8 Positions in Turbine vs. Velocity 21.3MW

4.4.5 Vibration in terms of Displacement (µm)

Table 4.9: Unit 1 at 34 MW (Full Load condition)

Table 4.10: Unit 1 at 23.1 MW (Part Load condition)

Table 4.11: Unit 2 at 34 MW (Part Load condition)

Table 4.12: Unit 2 at 23.1 MW (Part Load condition)

Figure 4.9: Frequency of Vibration in Unit 1

Figure 4.10: Frequency of Vibration in Unit 2

Figure 4.11: Displacement of Vibration in Unit 1

Figure 4.12: Displacement of Vibration in Unit 2

This decrease of displacement and increase of frequency at the part load indicates that the nature of vibration changes from low frequency-high amplitude to high frequency-low amplitude.

CHAPTER FIVE

MODELLING AND SIMULATION

5.1 Introduction

5.2 Computational Fluid Dynamics Analysis:

CFD is one of the tools for the simulation of fluid flow problems. It has various advantages like:

Low cost in designing phase
Less time consuming
More accurate than manual calculation for complex geometry like turbines

The main objectives of CFD analysis are as follows:

· To find out the critical region of erosion.

· To find out the best operating point in erosion point of view.

5.3 Different terms used in simulation:

A) Domain

B) General Erosion Model:

The fundamental and simplest equation of erosion is:

Erosion = f (operating condition, properties of particles, properties of base material)

Bardal describes the most general formula for pure erosion as:

W = K_mat. K_env.c. Vⁿ . f (α ) (mm/year)………………..eq.1

C) Boundary condition:

D) Inlet

The inlet boundary is the surface from where the fluid enters to the domain. We have used the normal velocity inlet boundary.

E) Outlet

The outlet boundary is the surface from where the fluid leaves the domain. We have used pressure outlet boundary.

F) Wall

The wall boundary is the water tight wall. It isolates the inner condition from the outer environment. All the restitution coefficients are defined in wall boundary.

5.4 Reference geometry

Figure 5.1: Reference Geometry of Blade and Guide Vane

Figure 5.2: Reference Geometry of Runner with Guide Vane

5.5 Simulation Results

The inputs for this process are velocity at inlet boundary and pressure at outlet boundary. The output of simulation is in the terms of velocity. It displays the velocity distribution in the domain.

The following are the velocity distribution profiles for full load and part load. These velocity distribution can be used to predict the erosion regions.

Figure 5.3: Velocity Profile at Full Load

Figure 5.4: Velocity Profile at Part Load

In case of guide vane, the velocity near the sealing region is increased at part load. It indicates that the erosion of guide vane increases, at part load.

CHAPTER SIX

CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

2) The critical regions of erosion as indicated by simulation are sealing regions of guide vanes; and leading and trailing ends of runner blades.

6.2 Recommendations

1. Erosion analysis by using appropriate erosion model is recommended.

2. The pressure variation at draft tube, compared with other hydropower station of similar capacity with no Air Admission System (Lower Marsyangdi Hydropower Plant) , would give better result.

3. Further research in evaluating the performance of desander is suggested.

4. It would be better to perform dynamic analysis of turbine model.

5. Noise measurement to relate it with the occurrence of cavitation is also recommended.

REFERENCES

· Dr. Jagadish Lal, Fluid Mechanics and Hydraulics, 10^th edition, published by Metropolitan Book Co. Pvt. Ltd.

Law, A. M., and W. D. Kelton. 1991. Simulation, Modeling and Analysis, second edition, Mc Graw-Hill
M. K. Natarajan, Principles of Fluid Mechanics Second Edition, OXFORD & IBH PUBLISHING CO. PVT.LTD.
R. K. RAJPUT, Textbook of Fluid Mechanics and Hydraulic Machines, S.CHAND AND COMPANY LTD., RAM NAGAR NEW DELHI-110055.
Thapa, Bhola, 2004.July,”Sand Erosion in Hydraulic Machinery”, MSc Thesis, Department of Mechanical Engineering
The license of ANSYS CFX software was used under the prior permission of Bim Prasad Shrestha, Head, Department of Mechanical Engineering, Kathmandu University.
Nepal Electricity Authority, A Year in Review – Fiscal Year 2009/10

[1] www.voithhydro.de/media/hypow_11_6.pdf

[2] www1.eere.energy.gov/industry/forest/pdfs/pulppaper_profile.pdf

[3] www.sari-energy.org/Publications/bbmalla.pdf

[4] Er. Suresh Raut, Final Year MSc Thesis, Department of Mechanical Engineering Tribhuvan University, Nepal.

[5] http://hydropower.inl.gov/turbines/pdfs/doeid-13741.pdf

[6] www.voithhydro.de/media/t3339e_Francis_72dpi.pdf

[7] www.tn.gov/environment/wpc/sed_ero_controlhandbook

[8] http://www.absoluteastronomy.com/topics/Cavitation

[9] http://www.featflow.de

[13]http//en.structurae.de/structure/data

[14]http://www.begellhouse.com/journals

[15]http://www.powervision-eng.ch/Profile/Publications/pdf/IAHR_2004.pdf

[16]http://acad-tim.tm.edu.ro/iSMART-flow/pdf/Muntean2_CIEM2009.pdf.

[17]http://jaibana.udea.edu.co/grupos/revista/revistas/.../Articulo%209.pdf

APPENDIX A: SEDIMENT DATA OF MARSYANGDI RIVER

Date	Reservoir water level	Intake (PPM)	De-sander (PPM)	Draft tube (PPM)	Gate opening( cm)			Remarks
Date	Reservoir water level	Intake (PPM)	De-sander (PPM)	Draft tube (PPM)	1	2	3	Remarks
7-Jul-10	622.35	3417			150
8-Jul-10	622.19	3279			160
9-Jul-10	622.28	3421			170
10-Jul-10	622.22	4889			235
11-Jul-10	622.19	5000			175
13-Jul-10	621.94	1122			125	50
14-Jul-10	622.03	1531					127
15-Jul-10	622.03	1692	1639	1475			133
17-Jul-10	622.98	5440	4615	2240		155		Highest ppm in draft tube
19-Jul-10	622.47	3469	2800	1818.2		145
21-Jul-10	622.14	1920	1718.8	1562.5			170
23-Jul-10	622.14	3556	960	937.5		171
25-Jul-10	622.03	3368	1111	1083.3	120	90
27-Jul-10	622.26	2558	2321	2667		200
29-Jul-10	621.98	2558	952	152		185
31-Jul-10	622.13	2609	1087	2459	90	140
2-Aug-10	622.03	2459	1522	667		150
4-Aug-10	621.77	1000	1087	682		180
6-Aug-10	622.23	2000	1304	1488		185
8-Aug-10	622.19	1538	1333	1000			140
10-Aug-10	622.04	971	591	434		125
12-Aug-10	622.16	581	434	321		145
14-Aug-10	622.13	824	696	786		130
16-Aug-10	621.97	2435	983	2210		1175		sand 57%silt 43%(intake)
18-Aug-10	622.13	2342	943	1787	100	100		sand 41%silt 59%(intake)
20-Aug-10	622.00	1002	754	1883	210			sand 48%silt 52%(intake)
22-Aug-10	622.08	1843	1676	735		252		sand 52.4%silt 47.6%(intake)
24-Aug-10	622.33	1647	734	719	155	73		sand 49.5%silt 50.5%(intake)
26-Aug-10	622.02	948	715	981	190			sand 47%silt 53%(intake)
28-Aug-10	622.13	2155	940	1609			220	sand 55%silt 45%(intake)
30-Aug-10	622.35	1827	961	1175	200	105		sand 49%silt 51%(intake)
1-Sep-10	622.1	2225	1372	1371	200	65		sand 65%silt 35%(intake)
3-Sep-10	622.03	2242	1537	167	210	55		sand 47%silt 53%(intake)
5-Sep-10	621.90	2009	671	65		250		sand 59%silt 41%(intake)
7-Sep-10	622.38	2374	717	651		210	119	sand 65%silt 35%(intake)
9-Sep-10	622.25	907	625	444		160		sand 58%silt 42%(intake)
11-Sep-10	622.40	717	338	491		165		sand 45%silt 55%(intake)
13-Sep-10	622.23	579	483	850		185		sand 51%silt 49%(intake)