TRIBHUVAN UNIVERSITY INSTITUTE OF ENGINEERING Central Campus, Pulchowk Lalitpur, Nepal
Department of Electrical Engineering
A field visit report on
Micro-hydro power
Submitted by:
Deepak Bhatta (069/BEL/315) Narayan Shrestha (069/BEL/324) Pradip Khatri (069/BEL/328) Saroj Sapkota (069/BEL/338) Umesh Pudasaini (069/BEL/347)
Submitted to:
Er. Dinesh GhimireABSTRACT
The main target for field visit to Malekhu micro hydro power plant was learning the operation, commissioning, design and technical aspects of the micro hydro power plant. The one-day program of the field visits to Malekhu Hydropower, Mahadevbesi made us familiar with the social, economic benefits to the local people. During the visit we measured the head by two methods: water filled tube and sighting meter method and discharge by using two methods: area velocity and salt gulp method. A small discussion and questioning-answering about the installation, construction, improved socioeconomic status was also carried out during the meeting held among our visit group and committee. All the economic status of the micro hydro was evaluated. The problem that they normally face and their periodic maintenance routine were discussed. The micro hydro plant has brought a lot of change in the villagers with development like transportation facility, access to good health service, good education facilities and increase in living standard. Total of 310 household are getting benefits from this micro hydro plant.
It has already been 5 years of its successful operation and it has showed its effect within this period and is seen technically and economically feasible and viable.
ACKNOWLEDGEMENT
We would like to thank our respected teacher Er. Dinesh Ghimire for providing us an opportunity to gain the practical knowledge about technical aspects of micro hydro plant through this field visit.
Secondly, we would like to express our special thanks to Department of Electrical Engineering, Central Campus Pulchowk who managed the wonderful field visit. We would like to express our gratitude towards Madhusudhan Shrestha sir of Department of Electrical Engineering,Pulchowk Campus for his supervision and assistance in Micro hydro field visit.
We would like to express our sincere thanks and gratitude to working committee of Malekhu khola Micro Hydro Power plant for explaining the system available there and providing the knowledge that we need for our study without which the visit would not be as successful. Also we are thankful to our respected teacher Madhusudan Shrestha for his valuable time and support to us. Also, we would like to thank all the teachers, friends and everyone who is directly or indirectly associated to make our visit successful.
INTRODUCTION
In context of Nepal, micro hydropower plant is a small scale hydropower plant of capacity 5 kW to 100 kW usually located in remote areas where there is no direct access to national grid that may be due geographical difficulties and economically unfeasible. Micro hydropower plant is the major source of energy in the rural areas and it is a practical and cost effective way of meeting the energy demand of people in rural areas. We visited the Malekhu Khola MHP of 26KW located at Mahadevbesi VDC, Dhading. There are middle and lower class villagers living together with dominatingly Chepang community and others people residing over there are Magars and Gurungs. Most of the villagers
there are engaged in agriculture. The micro hydro plant has brought a lot of
change in the villagers with development like transportation facility, access to good health service and increase in living standard.
OBJECTIVES
To learn operation, maintenance and design aspect of micro-hydro power plant.
Flow and head measurements in actual site. Micro-hydro plant design with measured discharge & head.
Sizing and selection of turbine and generator. To design appropriate ballast size.
To find out the total capital cost investment and calculate the cost per KW.
Socio-economic development in the society due to Micro-hydro Plant.
METHOLODOGY
BEFORE FIELD VISIT: Site selection.
Collection of documents and equipment to facilitate the visit. DURING FIELD VISIT:
Brief study of present scheme i.e. civil, electrical, mechanical etc. Measurement of head and discharge by various methods.
Meeting with local peoples, interactions and questioning-answering etc. AFTER FIELD VISIT:
Necessary calculation & selection of various components is done for designing.
Socio-Economic Condition
Ethnic groups:There are 310 households, which are benefited from this MHP scheme. The total population benefited by this project is about 1500. Communities like Tamang, Chhetri and Damai/Kami,brahaman are residing in the project area. chhetri holds the majority of almost more than 65% but other communities also are in same respect.
Economic condition
Economic condition of the village is not very sound. Illiteracy percentage is high. The main source of income of the people is agriculture. Almost 90% household depends upon agriculture. In average 4 persons per household are involved in agriculture. About 10% household depend on labor works; in an average one man per household is involved.
Land holdings and uses
Average land holdings per household in the project area are 5 ropanies. The major crops grown are rice, maize, wheat, millet, oilseeds etc. besides potatoes, garlic, beans and orange are major horticultural crops grown in the vicinity. Canal utilization on irrigation purpose
The main crops grown in the vicinity are rice, maize, wheat and vegetables. Implication of irrigation has increased the land yield. The water output for irrigation purpose is designed to be 12 l/s. with this large land has been irrigated under different cropping pattern.
Marketing and agricultural commodities
Farmers growing cereal crops generally get their cereal products milled at an agro-processing unit (Ghatta). Farmers engaged in vegetable growing sell their products to local main bazaar malakhu and products go to Kathmandu also for which middlemen plays significant role in determine price of the commoditized.
TECHNICAL DETAILS OF MALEKHU MICRO HYDRO PLANT
Gross head 25 m
Measured flow 350 l/sec may 1
Available flow 334 l/sec (driest flow)
Design flow 210 l/sec
Design power 26kW
Head race 1464 m, stone masonry
Diameter of penstock 325 mm 3 mm thick and 50 m long pipe
Types of penstock pipe Mild steel
Types of intake Side intake
Types of diversion Temporary weir
Types of turbine Cross flow
Turbine shaft power 40 kw
Mechanical Flat belt (habasit)
transmission
Generator
50 kVA,50 Hz synchronous generator,400/230 volt and 1500 rpm
ELC 26 kW
Ballast load Industrial immersion heater 35 kw
Total length of 10700 m
transmission and distribution
Types of conductor used
Rabbit conductor 17600 m and squirrel 20700 m
Name of the project
Malekhu khola village electrification project
Location Mahadevsthan vdc
District Dhading
Zone Bagmati
Name of the source Malekhu khola
No of house hold 310
Subscribed power 100 watt
Load centre
Ward no 1 2 4 and 5 of Mahadevsthan vdc
Route to reach site
Kathmandu- Malekhu (5 hours of walking)
MEASUREMENTS
The Measurement of discharge can be performed through the following techniques:
- Direct method
1.Area velocity: 2. Dilution techniques -Indirect methods:
1. Hydraulic structures –Weir 2. Slope area method
The methods generally used for flow measurement are: 1. Velocity Method.
2. Salt gulp Method. 3. Bucket Method.
Salt Dilution Method is mostly used in Micro Hydro.
Head Measurement can be performed through the following measures: 1. Water filled tube
2. Sighting meters
We measured the discharge using area velocity method and salt dilution method. Likewise, we measured the head using water filled tube and Abney levels.
Area Velocity method
This Method is based on the principle that for a fluid of constant density flowing through a cross-section, the product of cross-sectional area and mean velocity will be constant that is the discharge.
Q(m3/s) = Area(m2)× v
mean(m/s)
The most practical method of measuring stream discharge is through the velocity-area method. This method involves measuring the velocity of a neutral buoyancy object (e.g., wood, plastic bottles etc.) and multiplying this by the average cross-sectional area (using a tape and rule) of the river gives the discharge of that stream. These objects do, however, float close to the river
surface, which is faster than the average velocity of the water profile and must, therefore, be reduced by a coefficient called correction factor (in our case we chose the value of correction factor as 0.75).
Procedure:
Person X stays at upstream and person Y stays at down-stream at some measured distance. Person X then puts a float at a fairly fast moving point in the river and lets it sweep. The time in the stop watch is noted down when the float travels the prefixed distance.
The procedure is repeated 10 times with different floats. The distance travelled by the float divided by the time gives its surface velocity. This surface velocity is then multiplied by appropriate correction factor to find the mean velocity. Ten such mean velocities are calculated and mean is calculated.
The mean cross sectional area of the river is found by finding the mean depth and multiplied it by the width of the river. The mean depth is found by measuring depth at all locations from one side of the channel to the other side of the channel and taking a mean.
Observation table: Distance
travelled, Si m
Time taken to travel this distance, Ti sec. Surface velocity Vi = Si/Ti m/s 20 17.5 1.1428 20 23 0.868 20 19.2 1.0416 20 18 1.1 20 19 1.0526 20 17.1 1.168 20 17.96 1.1 20 19.17 1.0432 20 17.76 1.1249 Correction factor ( C.F) = 0.75
So, mean velocity with correction factor = 0.8037 m/sec
Area of cross section = mean depth of channel × width of the channel = 0.2514×1.35 = 0.3394 m2
Discharge (Q) = Area of cross section × Mean velocity = 0.3394×0.8037
= 0.2727 m3/s = 272.77 l/s
Salt gulp method
Salt Gulp method is easy to accomplish, reasonably accurate (error <7 %), and reliable in a wide range of stream types. It gives better results the more turbulent the stream. Using this approach, a spot check of stream flow can be taken in less than 10 minutes with very little equipment.
A bucket of heavily salted water is poured into the stream. The cloud of salty water in the stream starts to spread out while travelling downstream. At a certain point downstream it will have filled the width of the stream. The cloud will have a leading part which is weak in salt, a middle part which is strong in salt and a lagging part which is weak again. The saltiness (salinity) of the water can be measured with an electrical conductivity meter. If the stream is small, it will not dilute the salt very much, so the electrical conductivity of the cloud (which is greater the saltier the water) will be high. Therefore, low flows are indicated by high conductivity and vice versa. The flow rate is therefore inversely proportional to the degree of conductivity of the cloud.
The above argument assumes that the cloud passes the probe in the same time in each case. But the slower the flow, the longer the cloud takes to pass the probe. Thus flow is also inversely proportional to the cloud-passing time.
Observation table
Discharge Measurement Using Salt Gulp Method
S.N. Time (s) Conductivity (×10-6ohm-1) 1 5 4 2 10 4 3 15 4 4 20 4 5 25 4 6 30 4 7 35 5 8 40 11 9 45 16 10 50 15 11 55 14 12 60 12 13 65 9 14 70 6 15 75 5 16 80 4 17 85 4 18 90 4
Calculation of discharge
The observed value are plotted against time as below.
From this method:
1 M k Q A Where
A= area under the curve = 5×1×180 = 900 (each square box= 1×5 per ohm ×10-6, square box numbers= 180)
Q = Discharge in l/sec
m= mass of salt added in mg= 100g x 103 At 22°C k-1=2.04x10-6 ohm-1 per mg per l By using the formula, we got
HEAD MEASUREMENT Sighting Meters
Hand-held sighting meters (also known as Clinometers or Abney levels) can measure the angle of inclination of a slope. They can be very accurate if used by an experienced person. They are
Small and compact, and sometimes include range-finders which save the trouble of measuring linear distance. Since the method demands that the linear distance along the slope is recorded, it can have the advantage of measure of the length of penstock pipe as well.
Observation table S.N Angle(θ) degree Slope length(l)m Height(h)=l*sinθ , m 1 23 18 7.03 2 25 21 8.87 3 28 9 4.22 4 30 10 5 So, the total head measured =25.12 m
Water filled tube method
For this procedure the material required were U- pipe of 10 meters, staff of 2 nos.
Initially, Person X stays at uphill, Person Y stays at downhill. Person X matches water level at expected fore bay level. Person Y then measures height of this level at downhill. This is denoted by A1.
Person Y now stays at the same place and person X comes further downhill than Y. Person X then measures height A2 for a height B1 measured by Y.
Person X now stays at the same place and person Y comes further downhill than X. Person Y then measures height A3 for a height B2 measured by person X. This process continues till turbine level is reached.
Observation table:
Head measurement Using water filled tube and graded rod
OUR MICRO HYDRO POWER PLANT DESIGN CALCULATION: From the above findings, the installed capacity of the plant can be determined: Design discharge = 210 l/s
Gross head=24.715m Taking head loss = 10% Net head = gross head – head loss
=24.715 – 0.1×24.715 =22.2435 m ≌ 22 m
Overall Plant efficiency (η ) = ηcivil works× ηpenstock×ηturbine×ηgenerator× ηline = 0.95×0.90×0.75×0.85×0.97 = 0.5287 S. N. Downhill height (Ai m) Uphill height (Bi m) Hi=Ai-Bi 1 2.62 0 2.62 2 1.68 0.40 1.28 3 2.17 0.15 2.02 4 1.64 0.20 1.44 5 2.15 0.10 2.05 6 1.68 0.9 1.59 7 1.61 0.10 1.51 8 1.42 0.52 0.90 9 2.46 0.20 2.26 10 2.37 0.10 2.27 11 2.13 0.20 1.93 12 2.25 0.19 2.06 13 2.52 0.15 2.37 Total = 24.31 m
Turbine efficiency (ηturbine) = 0.75
Shaft power (P) = ηturbine ×Q×H/100 kW =0.75×210×22/100
=34.65 kW Plant Output = η× Q×H/100 kW
=0.5287×210×22/100 =23.96 kW
Taking the turbine speed as 500 rpm; specific speed is given as: Ns = N× (power output in kW)0.5/H5/4
=1.2×500× (34.65)0.5/225/4 =74.124
Constrained in the boundary marked by shaft power of 34.65 kW, net head 22 m, and a turbine speed of 500 rpm , the suitable turbine from the nomogram is cross flow turbine and Francis turbine. But from part flow efficiency point of view the cross flow turbine is most efficient . Also, during dry season, when the ratio of flow to maximum flow is less, then the
Francis turbine doesn’t prove to be efficient. Therefore, the cross flow turbine is selected.
Fig : Part flow efficiency of various turbines
Here We have selected the turbine speed 500 rpm. So we use the belt drive system. That means gear ratio = 3 as the speed of the generator 1500 rpm. Diameter of runner: 22 40 40 0.38 500 net ideal H D m rpm
Thickness of the water jet(ideal) tjet = 0.1 × Dideal to 0.2 × Dideal = 3.8 to 7.6 cm
The length of runner is given by 2 0.21 2 10 22 0.13 to 0.26 runner jet net jet Q L t gH t m
We can find the runner diameter from nomogram too, and we use the value obtained from nomogram for design purpose.
Fig : Nomogram for obtaining runner diameter
From nomogram, approximate runner diameter is 0.4 m.
Calculating tjet and lrunner accordingly using the formula mentioned above, we obtain, tjet = 0.1×0.4 = 0.04 m and lrunner = 0.25 m
THE GOVERNING SYSTEM
The governing system controls the speed of turbine-generator set in response to the change in load to the generator. As, the output voltage and frequency of the generator directly depends upon the speed of the turbine, hence there must be a provision for maintaining the voltage and frequency within a specified limit by regulating the speed. This can be achieved by employing a governor. The governor can be of the following two types :
Conventional governing
i. Oil pressure governor ii. Electronic load controller Non-conventional governor
The conventional governors wherein the speed is regulated by controlling the water inlet to the turbine, through hydraulic or mechanical governing system is much complicated to design and expensive to use in a small micro hydro system. Hence, an electronic load controller is preferred to be used as governor. An ELC with ballast load controls the speed of the turbine generator set by maintaining generator output constant at all times irrespective of the change in load by the consumers. The flow is kept constant to the turbine so speed remains constant. A constant generator output maintained by supplying a secondary ballast heaters with the power not needed by the consumer.
DESIGN OF ELC WITH BALLAST LOAD
Figure: ELC with ballast load Specifications:
Generator size = 23.96 KW Rated voltage of heater = 230 V
Considering the voltage drop of 10 volt across the ELC,Voltage across the terminals of ballast load = (230-0) V = 220V Temperature of entering water = 25° C
Temperature of outgoing water = 50° C Allowable temperature rise = 25° C Specific heat of water = 4200 J/Kg/K
Now we need to design the ballast load such that when all the loads are switched off, the ballast can safely dissipate the generated power without causing excessive temperature rise or damage.
Let us choose 3 kW water heater elements each containing a single heating element of 3 kW. Resistance of 3 kW element;
= (230)2/3000 = 17.63 Ω
When full load is diverted to the ballast, voltage across is only 220V. Power dissipated in each 3 kW element;
Power dissipated =(220)2/17.63 =2745.32 W =2.745 kW
Now, consider 10 such heating elements; Total power dissipated = 10*2.745 =27.45 kW (>23.96)
Percentage oversize = 14 % (<15%) So valid.
So we choose 10 numbers of 3 kW elements. Water flow rate
Q=ms×change in temp
Mass/second = (23.96×1000)/(4200×25) = 0.228 kg/s Flow rate required =0.228 l/s
Fig: Water heater with ballast loads
Fig. Heating element with 10 no. 3 kW element
SELECTION OF DRIVE SYSTEM
A drive system transmits the power from the turbine to the generator at the correct speed for the generator and in a suitable direction. The drive system comprises the generator shaft, turbine shaft, bearings, pulleys, belts, gearboxes, or other
components to change the speed or the orientation of the shafts. Different types of drive systems are:
1.Direct coupled drive system 2.Wedge belt drive system
3.Wedge belt drive system with extra bearings 4.Quarter turn belt drive
5.Direct coupled turbine and geared motor used as alternator 6.Turbine rotor mounted on generator shaft
In our design we have chosen horizontal arrangement of the turbine and the generator shaft, speed of rotation of turbine being 500 RPM and that of generator being 1500 RPM. So we have gear ratio of 3. Among the various types of drives stated above, wedge belt drive is the most suitable option. Characteristics of wedge belt drive system are listed below:
• Alternative arrangement could also be flat belt
• Axes of both turbine and generator could be vertical for both types of belts • Generator should be mounted on slide rails to obtain belt tensions
• The drive applies load to turbine and generator bearing/shaft • Turbine and generator may run at different speed
• Turbine and generator may be at different height
• Shafts must be parallel and pulleys in line but alignment is not as critical as for direct drive
Fig : Wedge belt drive system SELECTION OF GENERATOR
Either one of the following options can be selected: Induction generator
Synchronous generator
Self excited, Synchronous generator is selected for our design. It works on the principle:
“whenever the magnetic field linked with a conductor changes, an emf is induced across the conductor”. If a load is connected across the ends of this conductor, current will be supplied to it. A three phase synchronous generator is effective three single phase generators in one, using the same magnetic field.
Fig : Three phase star connected rotor and output voltage waveform
ampere rating compared to that required in the condition of maximum demand. i. This allows for possible expansion of the loads and supply systems.
ii. This minimizes momentary voltage reductions which occur when induction motors are started. The volt-amp rating of a generator should be more than five times the kW rating
of any induction motor (including those built into electrical appliances) which may be started ‘direct on line’.
iii. Over-rated generators will run cooler.
iv. Over-rated generators are necessary when using an ELC.
An additional 25% capacity on kVA should be made on this calculated figure to allow for motor starting currents and to extend the life of the alternator to be more in line with the other system components. The appropriate standard frame size is therefore 1.25 times more without ELC. The ELC varies the current flow to the ballast load by adjusting phase angle at which conduction starts. So if the current starts to flow to the ballast only after voltage waveform travels an angle α, the ballast load, though resistive, acts as if it were acting as a lagging power factor load. When the consumer load is also of lower power factor, the reactive power drawn from the generator is more which may damage the AVR and the generator winding. The condition is worse when ballast load is applied at a conduction angle of 90o.
To cater this situation, “add 60% rule” to select the size of the generator i.e. Generator kVA = (max kW load/power factor)×1.6
Required size of generator
It is a wiser practice to employ a generator having considerably larger volt- The generator of size 45.101 kVA may not be available in the market. So we go for next higher available generator which is 50 kVA.
EXCITATION SYSTEM
Unlike a dc generator, the output voltage of a simple synchronous generator falls very rapidly as the load current it supplies increases. This is due to an effect called ‘armature reaction’ caused by the load current ‘de-magnetizing’ the main field. As a result, it is essential that the main field dc magnetizing current is adjusted as the load current changes so that the output voltage remains the same for all loads. An ‘automatic voltage regulator’ (AVR) must therefore be provided to control the dc field current. A problem in micro-hydro set-ups is that low- speed running of the turbine and generator may occur for prolonged periods. The AVR may respond by boosting the excitation in order to raise output voltage but will be unable to do this continuously without overheating. The high field currents forced in this way have been known to destroy the generator, even on under speeds of only 5%.
Figure: Voltage frequency relationship
The dc field supply is provided by rectifying the ac output voltage. The ability of a self- excited synchronous generator to build up its field excitation when the machine is started depends on the residual magnetism in the iron core and this must not be lost. It should also be noted that an AVR is even more necessary in a self-excited synchronous generator than in the separately
Excited type as the dc field current supply voltage is directly dependent on, and thus decreases with, the ac output voltage.
TARIFF DESIGN
Tariff is the price paid by the entrepreneurs and householders for the use of electricity. The tariff are fixed on the basis of loan repayment, operation and maintenance cost and the welfare funds. There are some principles for fixing the tariffs. The tarrifs should be discussed among the villgers and arguments should be done on it. It should be workable in practice as well as it should match with the findings of capability and demand survey. It should have the provision for work replacement for underprivileged people. It should contain the advice of almost all the villagers.
COST ESTIMATION
Estimated Cost Categorisation: S. N. Description of items Amount 1 Installation supervision and commissioning charge 120000 2 Cost of civil construction 5850000 3 Cost of mechanical component 4262015 4 Cost of electrical component 4062015 5 Transportation cost 60755 6 Other Costs 379000 Total 145,33,7 85
Investment Capital categorization: S
n
Particulars Amoun
t 1 Expexted Subsidy from
Govt.
644000 0
2 Loan Form Bank 650000
0
locals
4 Investment from Locals 693785
Total Investment 145337
85
Load Distributions:
Considering the following loads will be probably incurred to the plant throughout the year:
S.N. Description Operating Time
Runnin
g Power consumed Energy
Hours (KW) Consumed KWHr 1 Lighting Loads 6pm-12pm; 4am- 9 12 108 7am
2 Rice mill * 2 12am to 6 pm 6 12 72
3 Battery charging 10am to 6 pm 8 2 16
4 Other Residential 6 am- 12pm 18 3 54 Loads Energy Consumed 250 Per Day
Total Energy Consumed per day= 250 KWHr Total Energy Generated per day =24Hr ×23.96KW
= 575.04 KWHr
Considering outage of 1 month per year for maintenance and failures: Enerrgy Consumed 250
Plant factor 0.4
Energy Generated 575.04
Plant Factor
Investment Excluding Subsidy from Government = Rs 65,00,000
This amount must be considered to be returned in payback period of 6 yrs with Rate of return of 10%
So Annual Cost should be
6 6 (1 ) 0.1 1.1 65,00,000 14,92, 449 (1 ) 1 1.1 1 n n r r A P r
Operation and maintenance cost = 6% of Total Investment = Rs 89,546 Total Annual Cost = Rs
1581995/-So per watt cost should be = 1581995
23.96100012 =Rs 5.5/ Watt/ month
Considering Rs 6/Watt/month, Yearly income = 6×23.96×1000×12 = 1725120/-Now Yearly Welfare Fund savings=1725120 – 1581995=Rs
1,43,125/-Summary:
Name of Project : Malekhu Khola, MHP
Location : Mahadevsthan Malekhu
District : Dhading
Zone : Bagmati
Name of Source : Malekhu Khola No. of household Benefit : 310
Electricity demand per house: 100W Ownership: Community
Technical features
Net Head = 22 m Measured Discharge = 270 l/s Design discharge = 210 l/s
Plant Output = 23.96 kW
Turbine = Crossflow
Ballast = Water heater
Ballast Size = 27kW
Belt = Wedge Belt
Generator = Synchronous
Generator Size = 50kVA
Plant factor = 0.4
Tariff = Rs 6/Watt/month
CONCLUSION
The field visit to Mahadevsthan micro hydropower proved to be very useful to us. We learnt operation, maintenance and design aspect of micro-hydro power plant. We measured the flow and head measurements in actual site by using practical methods and performed load survey demand in actual site but there was little deviation in measured data when compared to actual data given. We were able to observe practically what we have theoretically learnt. By using what the data that we obtained from our experiments, we designed a micro hydro plant with all the components like ELC, generator, turbine, drive system, etc. by ourselves and compared it with that in the site. Hence, it was very useful visit as a part of study.