1

CASE STUDY AND ANALYSIS OF MICRO

HYDRO POWER PLANT

(DAPUR MAIDAN, DIR LOWER KPK)

Muqeem Ud Din

Umar Farooq

Supervised by:

Engr. Naveed Ullah

Final year project 2011-2012, submitted as a partial fulfillment for

the Degree of B.Sc in Mechanical Engineering

DEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY OF ENGINEERING & TECHNOLOGY,

PESHAWAR

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CASE STUDY AND ANALYSIS OF MICRO

HYDRO POWER PLANT

(DAPUR MAIDAN, DIR LOWER KPK)

Muqeem Ud Din

Umar Farooq

_______________

Engr. Naveed Ullah

Project Supervisor

___________________

Prof. Saeed Javed Tajik

Chairman

FINAL YEAR PROJECT 2011-2012

DEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY OF ENGINEERING & TECHNOLOGY,

PESHAWAR

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ABSTRACT

The total available hydro power potential in Khyber Pukhtunkhwa is about 30000MW

in which 18% has been harnessed. Local communities living in distant far and flung

mountainous areas are still in dark and lack resources and development. MHPPs could

bring revolutionary change in their lives and help in the development of society.

NGOs and local communities have installed MHPPs but most often with locally built

accessories and average expertise. The aim of this project was to analyze the already

installed MHPPs in KPK by considering a case study and to recommend for

improvement. In order to accomplish this objective, extensive literature review has

been carried out. For site selection and acquisition of data regarding MHPPs in KPK,

various GOVT. and Non-Govt. organizations have been consulted. Different sites

were visited and finally a 10 KW MHPP was selected in “Dapor Maidan” Dir (l). For

evaluation of the site, theoretical power output was calculated after finding site

parameters. Efficiency was calculated which was 21.76%. The much lower efficiency

than optimum range (60-75%) depicted shortcomings in civil structures and electro

mechanical components. Finally causes of limitations were identified and

recommendations were made for the improvement of efficiency.

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ACKNOWLEDGMENT

Special gratitude to Engr. Navidullah, Semester Coordinator Mechanical Department

UET Peshawar, for his matchless support and guidance. We would like to thank Prof

Iftikhar, Director Undergraduate and Prof Saeed javid Tajik, Chairman Mechanical

Department for their support. We acknowledge the helping hand extend to us from

SHYDO( Sarhad Hydal Development Organization), PCRET( Pakistan council of

renewable energy and technology) and SRSP( Sarhad Rural Support Program).

Thanks to Asmatullah, our host in Maidan dir (l) who cordially helped us in arranging

visits to site and accompany us.

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CHAPTER 1

INTRODUCTION

The objective of a hydro power scheme is to convert the potential energy of a

mass of water, flowing in a stream with a certain fall (termed the head.), into electric

energy at the lower end of the scheme, where the powerhouse is located.

The power of the scheme is proportional to the flow and to the head. Micro-

hydro schemes produce power from streams and small rivers. The power can be used

to generate electricity, or to drive machinery. Micro-hydro can bring electricity to

remote communities for the first time, replacing kerosene for lighting, providing TV

and communications to homes and community buildings, and enabling small

businesses to start.

Micro-hydro schemes are already benefiting many remote communities and

hilly areas of Pakistan. In the developed world, micro-hydro schemes supply power to

existing mains electric grids.

Figure 1.1 Micro hydro power system

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1.1. HISTORY OF SMALL HYDRO POWER TECHNALOGY

Hydropower is a renewable, non-polluting and environmentally benign source of

energy. Hydropower is based on simple concepts. Moving water turns a turbine, the

turbine spins a generator, and electricity is produced. Many other components may be

in a system, but it all begins with the energy in the moving water. The use of water

falling through a height has been utilized as a source of energy since a long time. It is

perhaps the oldest renewable energy technique known to the mankind for mechanical

energy conversion as well as electricity generation. In the ancient times waterwheels

were used extensively, but it was only at the beginning of the 19th Century with the

invention of the hydro turbines that the use of hydropower got popularized.

Small-scale hydropower was the most common way of electricity generating in

the early 20th

century. The first commercial use of hydroelectric power to produce

electricity was a waterwheel on the Fox River in Wisconsin in 1882 that supplied

power for lighting to two paper mills and a house. Within a matter of weeks of this

installation, a power plant was also put into commercial service at Minneapolis. India

has a century old history of hydropower and the beginning was from small hydro. The

first hydro power plant was of 130 kW set up in Darjeeling during 1897, marked the

development of hydropower in the country. Similarly, by 1924 Switzerland had nearly

7000 small scale hydropower stations in use. Even today, Small hydro is the largest

contributor of electricity from renewable energy sources, both at European and world

level. With the advancement of technology, and increasing requirement of electricity,

the thrust of electricity generation was shifted to large size hydro and thermal power

stations. However, it is only during the last two decades that there is a renewed

interest in the development of small hydro power (SHP) projects mainly due to its

benefits particularly concerning environment and ability to produce power in remote

areas. Small hydro projects are economically viable and have relatively short

gestation period. The major constraints associated with large hydro projects are

usually not encountered in small hydro projects. Renewed interest in the technology

of small scale hydropower actually started in China which has more than 85,000

small-scale electricity Hydropower stations which will continue to play important role

throughout the 21st Century, in world electricity supply. Hydropower development

does have some challenges besides the technical, economic introducing, hydropower

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plants environmental advantages it shares above other power generation (fossil fuel

based) technologies.

At the beginning of the new Millennium hydropower provided almost 20%

(2600 TWh/year) of the electricity world consumption (12900 TWh/year). It plays a

major role in several countries. According to a study of hydropower resources in 175

countries, more than 150 have hydropower resources. For 65 of them, hydro produces

more than 50% of electricity; for 24, more than 90% and 10 countries have almost all

their electricity requirements met through hydropower.

1.2 SMALL HYDRO POWER PROJECT

CLASSIFICATION

Hydro power projects are generally categorized in two segments i.e. small

and large hydro. Different countries are following different norms keeping the upper

limit of small hydro ranging from 5 to 50 MW. The world over, however, there is no

consensus on the definition of small hydropower. Some countries like Portugal, Spain,

Ireland, Greece and Belgium, accept 10 MW as the upper limit for installed capacity.

In Italy the limit is fixed at 3 MW (plants with larger installed power should sell their

electricity at lower prices) and in Sweden 1.5 MW. In France the limit has been

recently established at 12 MW, not as an explicit limit of MHPP, but as the maximum

value of installed power for which the grid has the obligation to buy electricity from

renewable energy sources. In the UK 20MW is generally accepted as the threshold for

small hydro. Though different countries have different criteria to classify hydro power

plants, a general classification of hydro power plants is as follows:

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Table 1.1 Hydro power plants classification

Apart from the above classification, some of the other terms in vogue

nowadays when describing very small hydro power plants are „Pico Hydro‟ (less than

5 kW) and „Tiny Hydro‟ (less than 1kW).Small hydro plants are also classified

according to the “Head” or the vertical distance through which the water is made to

impact the turbines. The usual classifications are given below:

Table 1.2 MHPP classifications on basis of Head

Type Head range

High head 100m and above

Medium head 30-100m

Low head 2- 30m

These ranges are not rigid but are merely means of categorizing sites.

Schemes can also be defined as:-

Run-of-river schemes

Schemes with the powerhouse located at the base of a dam

Schemes integrated on a canal or in a water supply pipe

Type Capacity

Large- hydro More than 100 MW and usually feeding into large electricity grid

Medium-hydro 15-100 MW usually feeding a grid

Small-hydro 1-15 MW usually feeding into a grid

Mini- hydro Above 100KW but below 1MW;either stand alone schemes or

more often feeding into the grid

Micro-hydro From 5KW up to 100KW;usually provided power for small

community or rural industry in remote areas away from grid

Pico-hydro From a few hundred watts up to 5KW

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Most of the small hydro power plants are “run-of-river” schemes, implying that

they do not have any water storage capability. The power is generated only when

enough water is available from the river/stream. When the stream/river flow reduces

below the design flow value, the generation ceases as the water does not flow through

the intake structure into the turbines. Small hydro plants may be stand alone systems

in isolated areas/sites, but could also be grid connected (either local grids or

regional/national grids). The connection to the grid has the advantage of easier control

of the electrical system frequency of the electricity, but has the disadvantage of being

tripped off the system due to problems outside of the plant operator‟s control.

1.3 GENERAL PRINCIPLE OF MHPP

Power generation from water depends upon a combination of head and flow.

Both must be available to produce electricity. Water is diverted from a stream into a

pipeline, where it is directed downhill and through the turbine (flow). The vertical

drop (head) creates pressure at the bottom end of the pipeline. The pressurized water

emerging from the end of the pipe creates the force that drives the turbine. The turbine

in turn drives the generator where electrical power is produced. More flow or more

head produces more electricity. Electrical power output will always be slightly less

than water power input due to turbine and system inefficiencies.

Water pressure or Head is created by the difference in elevation between the

water intake and the turbine. Head can be expressed as vertical distance (feet or

meters), or as pressure, such as pounds per square inch (psi). Net head is the pressure

available at the turbine when water is flowing, which will always be less than the

pressure when the water flow is turned off (static head), due to the friction between

the water and the pipe. Pipeline diameter also has an effect on net head.

Flow is quantity of water available, and is expressed as „volume per unit of

time‟, such as gallons per minute (gpm), cubic meters per second (m3/s), or liters per

minute (lpm). Design flow is the maximum flow for which the hydro system is

designed. It will likely be less than the maximum flow of the stream (especially

during the rainy season), more than the minimum flow, and a compromise between

potential electrical output and system cost.

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1.4 POWER FROM MHPP

To know the power potential of water in a stream it is necessary to know the

flow quantity of water available from the stream (for power generation) and the

available head. The quantity of water available for power generation is the amount of

water (in m3 or liters) which can be diverted through an intake into the pipeline

(penstock) in a certain amount of time. This is normally expressed in cubic meters per

second (m3/s) or in liters per second (l/s). Head is the vertical difference in level (in

meters) through which the water falls down.

The theoretical power (P) available from a given head of water is in exact proportion

to the head and the quantity of water available.

P= Q × H × e × 9.81 (kW) 1.1

Where,

P = Power at the generator terminal, in kilowatts (kW)

H = the gross head from the pipeline intake to the tail water in meters (m)

Q = Flow in pipeline, in cubic meters per second (m3/s)

e = the efficiency of the plant, considering head loss in the pipeline and the efficiency

of the

Turbine and generator, expressed by a decimal (e.g. 85% efficiency= 0.85)

9.81 is a constant and is the product of the density of water and the acceleration due to

gravity

This available power will be converted by the hydro turbine in mechanical power.

1.5 COMPONENTS OF A MICRO HYDRO SYSTEM Basic components of a typical micro-hydro system are as follows:

• Civil works components (headwork, intake, gravel trap with spillway, headrace

canal, forebay and distilling basin, penstock pipe, powerhouse and tailrace)

• Powerhouse components (turbines, generators, drive systems and controllers)

• Transmission/distribution network

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1.6 SYSTEM LAYOUT

The three types of waterway routes shown below are examples of possible

layouts of micro-hydropower system. The „short penstock‟ option, in most cases, is

considered the most economic scheme, but this is not necessarily the case.

Figure 1.2 Channel and penstock options

1.6.1 SHORT PENSTOCK

In this case, the penstock is short but the channel is long. The long channel is

exposed to the greater risk of blockage, or of collapse or deterioration as a result of

poor maintenance. Installing the channel across a steep slope may be difficult and

expensive. The risk that the steep slope may erode makes the short penstock layout an

unacceptable option, because the projected operation and maintenance cost of the

scheme could be very expensive, and it may outweigh the benefit of initial purchase

cost.

1.6.2 LONG PENSTOCK

In this case, the penstock follows the river. If this layout is necessary,

because the terrain would not allow the construction of a channel, certain precautions

must be taken. The most important consideration is to ensure that seasonal flooding of

the river will not damage or deteriorate the penstock. It is also important to calculate

the most economic diameter of penstock; in the case of a long penstock, the cost will

be particularly high.

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1.9.3 MID-LENGTH PENSTOCK

The mid-length penstock may cost more than the short penstock, but the cost of

constructing channel that can safely cross the steep slope may also be avoided. Even

if the initial purchase and construction costs are greater in this case, this option may

be preferable in case there are signs of instability in the steep slope.

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CHAPTER 2

HYDRAULIC STRUCTURES

2.1 WEIR & INTAKE

The large majority of small hydro schemes are of the run-of-river type, where

electricity is generated from discharges larger than the minimum required to operate

the turbine. In these schemes a low diversion structure is built on the streambed to

divert the required flow whilst the rest of the water continues to overflow it. When the

scheme is large enough this diversion structure becomes a small dam, commonly

known as a weir, whose role is not to store the water but to increase the level of the

water surface so the flow can enter into the intake. Sometimes, in remote hilly

regions, where annual flooding is common it may be prudent to build temporary weir

using local resources and manpower. The temporary weir is a simple structure at low

cost using local labor, skills and materials. It is expected to be destroyed by annual or

bi-annual flooding. However, advanced planning has to be done for rebuilding of the

weir. The intake of a MHPP is designed to divert only a portion of the stream flow or

the complete flow– depending upon the flow conditions and the requirement. MHPP

schemes use different types of intakes distinguished by the method used to divert the

water into the intake. For MHPP schemes, intake systems are smaller and simpler.

The following three types of intakes have been described here: side intake with and

without a weir and the bottom intake.

Side intake with weir: The weir used in this arrangement can be partly or

completely submerged into the water.

Bottom intake: At a bottom intake the whole weir is submerged into the

water. Excess water will pass the intake by flowing over the weir.

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2.1.1 SIDE INTAKE HEIGHT CALCULATION

In the case of side intake, following Case (a) or Case (b), whichever is higher, is

adopted.

a. Weir height (D1) determined in relation to the bed elevation of the scour gate of the

Intake weir

D1 = d1 + hi 2.1

b. Weir height (D2) determined by the bed gradient of the settling basin

D2 = d2 + hi+ L (ic – ir) 2.2

Where,

d1: height from the bed of the scour gate to the bed of the inlet (usually 0.5 – 1.0 m)

d2: difference between the bed of the scour gate of the settling basin and the river bed

at the same location (usually around 0.5 m) hi : water depth of the inlet (usually

determined to make the inflow velocity approximately 0.5 – 1.0 m/s)

L: length of the settling basin ic: inclination of the settling basin bed (usually around

1/20 – 1/30) ir: present inclination of the river

Figure 2.1 Sectional view of side intake and weir

2.1.2 TYROLEAN INTAKE HIGHT CACULATION

A Tyrolean intake where water is taken from the bottom assumes that the front of the

weir is filled with sediment and, therefore, the weir height is determined by Case D2

for side intake.

D2 = d2 + hi + L (ic – ir) 2.3

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Figure 2.2 Sectional view of Tyrolean intake and weir

Figure 2.3 Tyrolean Intake

2.2 POWER CHANNEL

The power channel or simply a channel conducts the water from the intake to

the FBT. The length of a channel depends upon the topography of the region and the

distance of powerhouses from the intake. Also the designing of the MHPP systems

states the length of the channel – sometimes a long channel combined with a short

penstock can be cheaper or required, while in other cases a combination of short

channel with long penstock would be more suitable. Generally power channels are

excavated and to reduce friction and prevent leakages these are often lined with

cement, clay or polythene sheet. Size and shape of a channel and material used for

lining are often a dictated by cost and head considerations. During the process of

flowing past the walls and bed material, the water loses energy. The rougher the

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material, the greater the friction loss and higher is the elevation difference needed

between channel entry and exit. In hilly regions it is common that the power channel

would have to cross small streams. In such situations it is often prudent to build a

complete crossing over the channel, as during rainy season, flash floods and/or

rocks/mud may block the channel or worse still, wash away sections of the channel.

Sometimes just the provision of a drain running under the channel (in case of very

small streams along stable slope) is usually adequate.

2.2.1 TYPES AND BASIC STRUCTURE OF HEADRACE CANAL

Headraces, that have a function to covey water from intake to forebay/head

tank, are classified into pressure waterways and non-pressure waterways. In term of

hydraulics, non-pressure waterways are open channel and the pressure waterway is a

conduit. The headrace structures are open canal, covered canal, culvert, tunnel,

aqueduct, inverter siphon, etc. Because of the generally small amount of water

conveyance, the headrace for a small-scale hydropower plant basically adopts an

exposed structure, such as an open channel or a covered channel, etc. In general, the

construction cost of open channel is the most economical.

2.2.2 HEAD RACE DESIGN

The size of cross section and slope should be determined in such a matter that

the required turbine discharge can be economically guided to the head tank.

Generally, the size of cross section is closely related to the slope. The slope of

headrace should be made gentler for reducing head loss (difference between water

level at intake and at head tank) but this cause a lower velocity and thus a lager cross

section. On the contrary, a steeper slope will create a higher velocity and smaller

section but also a lager head loss.

Generally, in the case of small-hydro scheme, the slope of headrace will be

determined as 1/500 – 1/1,500. However in the case of micro-hydro scheme, the slope

will be determined as 1/50 –1/500, due to low skill on the survey of leveling and

construction by local contractor.

The cross section of headrace is determined by following method:

Method of calculation:

Qd= A ×R 2/3×SL 1/2 ／n 2.4

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Where;

Qd: design discharge for headrace (m3/s)

A: area of cross section (m2)

R: R=A／P (m)

P: length of wet sides (m) refers to next figure.

SL: longitudinal slope of headrace (e.g. SL= 1/100=0.01)

n: coefficient of roughness

2.2.3 SETTLING BASIN

The water diverted from the stream and carried by the channel usually carries

a suspension of small particles such as sand that are hard and abrasive and can cause

expensive damage and rapid wear to turbine runners. To get rid of such particles and

sediments, the water flow is allowed to slow down in „settling basins‟ so that the sand

and silt particles settle on the basin floor. The deposits are then periodically flushed.

The design of settling basin depends upon the flow quantity, speed of flow and

the tolerance level of the turbine (smallest particle that can be allowed). The

maximum speed of the water in the settling basin can thus be calculated as slower the

flow, lower is the carrying capacity of the water. The flow speed in the settling basin

can be lowered by increasing the cross section area. The settling basin must have a

structure which is capable of settling and removing sediment with a minimum size

which could have an adverse effect on the turbine and also a spillway to prevent

excessive water inflow into the headrace. The basic configuration of a settling basin is

illustrated below.

Figure 2.4 Basic component of Settling Basin

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Each of these sections has the following function.

Conduit section: Conduit section connects the intake with the settling basin.

It is necessary that the conduit section should be curtailing its length.

Widening section: This regulates water flow from the conduit channel to

prevent the occurrence of whirl pools and turbulent flow and reduces the flow

velocity inside the settling basin to a predetermined.

Settling section: This section functions to settle sediment above a certain size

and its required length (l) is calculated by the following formula based on the

relation between the settling speed, flow velocity in the settling basin and

water depth.

The length of the settling basin (Ls) is usually determined so as to incorporate a

margin to double the calculated length by the said formula

2.5

Where

l: minimum length of settling basin (m)

hs: water depth of settling basin (m)

U: marginal settling speed for sediment to be settled (m/s) usually around 0.1 m/s for

a target grain size of 0.5 – 1 mm.

V: mean flow velocity in settling basin (m/s) usually around 0.3 m/s but up to 0.6 m/s

is tolerated in the case where the width of the settling basin is restricted.

V = Qd/(B×hs) 2.6

Qd: design discharge (m3/s)

B: width of settling basin (m)

Sediment pit: This is the area in which sediment is deposited

2.2.4 SPILLWAYS

Spillways along the power channel are designed to permit overflow at

certain points along the channel. The spillway acts as a flow regulator for the channel.

During floods the water flow through the intake can be twice the normal channel

flow, so the spillway must be large enough to divert this excess flow. The spillway

can also be designed with control gates to empty the channel. The spillway should be

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designed in such a manner that the excess flow is fed back to the river without

damaging the foundations of the channel.

Spillway drains the submerged inflow which flows from the intake. The sizes of

spillway will

be decided by following equation.

Qf= C×Bsp×hsp1.5 →hsp={Qf /(C×Bsp)}1/1.5 2.7

Where

Qf: inflow volume of submerged orifice (m3/s, see Figure 2.4)

C: coefficient =1.80

hsp: water depth at the spillway (m, see Figure 2.4)

Bsp: width of the spillway (m, see Figure 2.4)

2.3 FOREBAY/HEAD TANK

The FBT serves the purpose of providing steady and continuous flow into the

turbine through the penstocks. Forebay also acts as the last settling basin and allows

the last particles to settle down before the water enters the penstock. Forebay can also

be a reservoir to store water –depending on its size (large dams or reservoirs in large

hydropower schemes are technically forebay).

A sluice will make it possible to close the entrance to the penstock. In front of

the penstock a trash rack need to be installed to prevent large particles to enter the

penstock. A spillway completes the FBT.

2.3.1 HEAD TANK CAPACITY

The head tank capacity is defined the water depth from hc to h0 in the FBT length L

as shown in Figure

Figure 2.5 Picture of head tank capacity

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Head tank capacity

Vsc = As×dsc＝B×L×dsc 2.8

where

As: area of head tank

B : width of head tank

L: length of head tank

dsc: water depth from uniform flow depth of a headrace when using maximum

discharge (h0) to critical depth from top of a dike for sand trap in a head tank (hc)

In oblong section, uniform flow depth:

ho=H×0.1／(SLE)0.5 2.9

SLe: slope of tail end of the headrace

critical depth:

hc= {(α×Qd2) ／(g×B2)}1/3 2.10

α: 1.1 g : 9.8

2.3.2 DETERMINATION OF HEAD TANK CAPACITY

The head tank capacity should be determined in consideration of load control method

and discharge method as mentioned below.

In case only the load is controlled: The case only control load (demand)

fluctuation is considered, a dummy load governor is adopted. A dummy load

governor is composed of water-cooled heater or air-cooled heater, difference

of electric power between generated in powerhouse and actual load is made to

absorb heater. The discharge control is not performed. The FBT capacity

should be secured only to absorb the pulsation from headrace that is about 10

times to 20 times of the design discharge (Qd). A view showing a frame format

of load controlled by a dummy load governor is shown in figure 2.5

Figure 2.6 Pattern diagram of dummy load consumption

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In case both load and discharge is controlled: In the case of controlled both

load and discharge, it used for load control a mechanical governor or electrical

governor. These governors have function of control vane operation to optimal

discharge when electrical load has changed. Generally a mechanical governor

is not sensitive response to load change; FBT capacity in this case should be

secured 120 times to 180 times of Qd. On the other hand, an electrical

governor will response of load change, therefore FBT capacity is usually

designed about 30 times to 60 times of Qd.

2.4 PENSTOCK

The penstock is the pipe which conveys water under pressure from the FBT to

the turbine. Penstock is a significant component of the MHPP scheme and needs to be

designed and selected carefully as it represents a major expense in the total budget

(for some high head installations this alone could cost as much as 30% of the total

costs). Here the main aspects to consider are head loss and capital cost. Head loss due

to friction in the pipe decreases dramatically with increasing pipe diameter.

Conversely, pipe costs increase steeply with diameter. Therefore a compromise

between cost and performance is considered for design and selection of pipe diameter

and material.

While designing penstocks, the first principle is to identify available pipe

options and then to decided upon acceptable head loss (5% of the gross head is

generally considered). The details of the pipes of various materials and diameters with

losses close to this target are then tabulated and compared for cost effectiveness. A

smaller penstock may be lighter on pocket, but the extra head loss may account for

lost revenue from generated electricity each year.

2.4.1 PENSTOCK MATERIALS

The factors to be considered while deciding upon the material to be used for a

particular penstock are:

terrain,

soil type

weather conditions

Weight and ease of installation,

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accessibility of the site

likelihood of structural damage availability

surface roughness,

design life and maintenance

method of jointing design pressure

Relative cost.

The following materials can be considered for use as penstock pipes in micro hydro

schemes:

wooden planks or tree bark (for very small installations)

Spun ductile iron

GI Pipes

mild steel,

unclassified polyvinyl chloride (UPVC),

high density polyethylene (HDPE),

asbestos cement,

Pre stressed concrete,

Glass reinforced plastic (GRP).

Mild steel, UPVC and HDPE are the most common used materials.

2.4.2 CALCULATION OF STEEL PIPE THIKNESS

The minimum thickness of steel pipe of penstock is determined by following formula

2.11

Where

T0: minimum thickness of pipe

P: design water pressure i.e. hydrostatic pressure + water hammer (kgf/cm2), in

Micro-hydro scheme P=1.1×hydrostatic pressure.

For instance, if the head (Hp, refer to following figure) which from FBT to

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Turbine is 25m, P=2.5×1.1=2.75 kgf/cm2.

d: inside diameter (cm)

θa: admissible stress (kgf/cm2) SS400: 1300kgf/cm

2

η: welding efficiency (0.85～0.9)

δt: margin (0.15cm in general)

2.4.3 PENSTOCK DIAMETER

The diameter is selected as the result of a trade-off between penstock cost and

power losses. A simple criterion for diameter selection is to limit the head loss to a

certain percentage. Loss in power of 4% is usually acceptable. A more rigorous

approach is to select several possible diameters, computing power and annual energy.

The present value of this energy loss over the life of the plant is calculated and plotted

for each diameter. In the other side the cost of the pipe for each diameter is also

calculated and plotted. Both curves are added graphically and the optimum diameter

would be that closest to the theoretical optimum. Actually the main head loss in a

pressure pipe are friction losses; the head losses due to turbulence passing through the

trashrack, in the entrance to the pipe, in bends, expansions, contractions and valves

are minor losses. Consequently a first approach will suffice to compute the friction

losses, using for example the Manning equation

2.12

2.13

2.14

2.4.4 PENSTOCK JOINING

Pipes are generally available in standard lengths (it is easier for transportation

also) and have to be joined together on site. There are several methods of joining

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penstock pipes and the factors to be considered when choosing the best joint system

for a particular scheme are:

pipe material,

whether any degree of joint flexibility is required,

ease of installation

skill level of personnel,

Costs.

Generally, the pipes are joined by one of the following four methods:

flanged,

spigot and socket,

mechanical,

Welded.

2.4.5 BURYING OR SUPPORTING THE PENSTOCK

Penstock pipelines can either be laid upon the surface or buried underground.

This generally depends upon the material of the pipe, the nature of the terrain and

environmental and cost considerations.

While burying a penstock, it is very important to ensure proper installation

because any subsequent problems such as leaks are much harder to detect and resolve.

In case vehicles are likely to cross over the buried pipelines, they must be buried at

least 750 -1000 mm below ground level. Burying the pipeline carefully and correctly

enhances the life of the MHPP scheme and greatly reduces the chances of disruption

in power generation especially in hilly terrain with heavy landslides.

If the natural terrain does not permit burying the penstock then the penstock is

run over ground. In such conditions piers, anchors and thrust blocks are needed to

stabilize the pipeline (especially if these happen to be very long) to withstand the

weight of the pipes plus water and expansion and contraction of the pipe (due to

changing temperature).

Support piers are used basically to bear the weight of the pipes plus water

being carried. Anchors are large structures fixed along the length of a penstock,

restraining all movements (horizontal or vertical) by anchoring the penstock to the

ground. For a bend or contraction in the pipeline, a thrust block is used to oppose the

specific force generated by the bend or contraction. All of these structures are usually

25

built of rubble masonry or cement concrete. Sometimes, the anchor blocks may need

steel reinforcement (for long pipelines).

2.5 TAIL RACE

After passing through the turbine the water returns to the river trough a short

canal called a tailrace. Impulse turbines can have relatively high exit velocities, so the

tailrace should be designed to ensure that the powerhouse would not be undermined.

Protection with rock riprap or concrete aprons should be provided between the

powerhouse and the stream. The design should also ensure that during relatively high

flows the water in the tailrace does not rise so far that it interferes with the turbine

runner. With a reaction turbine the level of the water in the tailrace influences the

operation of the turbine and more specifically the onset of cavitations. This level also

determines the available net head and in low head systems may have a decisive

influence on the economic results.

2.6 FOUNDATION OF POWER HOUSE

Powerhouse can be classified into „the above ground type‟, the semi-

underground type‟ and „the underground type‟. Most of small-scale hydropower

plants are of „the above ground type, The dimensions for the floor of powerhouse as

well as the layout of main and auxiliary equipment should be determined by taking

into account convenience during operation, maintenance and installation work, and

the floor area should be effectively utilized. Various types of foundation for

powerhouse can be considered depending on the type of turbine. However the types of

foundation for powerhouse can be classified into „for Impulse turbine‟ (such as Pelton

turbine, Turgo turbine and Cross flow turbine) and „for Reaction turbine‟ (Francis

turbine, Propeller turbine)

2.6.1 FOUNDATION FOR IMPULSE TURBINE

In case of impulse turbine, the water which passed by the runner is directly

discharged into air at tailrace. The water surface under the turbine will be turbulent.

Therefore the clearance between the slab of powerhouse and water surface at the

afterbay should be kept at least 30-50cm.

26

2.13

Where,

hc: water depth at after bay (m)

Qd: design discharge (m3/s)

b: width of tailrace channel (m)

The water level at the after bay should be higher than estimated flood water level.

Then in case of impulse turbine, the head between the center of turbine and water

level at the outlet became head loss.

Figure 2.7 Foundation of Powerhouse for Impulse turbine

2.6.2 FOUNDATION FOR REACTION TURBINE

In case of reaction turbine, the head between center of turbine and water-

level can be use for power generation. Then it is possible that turbine is installed

under flood water level on condition to furnish the following equipment:

a. Tailrace Gat b. Pump at powerhouse

27

Figure 2.8 Foundation of Powerhouse for Reaction turbine

2.7 HYDROULIC STRUCTURES OVER THE SITE

We have selected a Run of river site in the hilly area of district Dir (L).the

MHPP is located on the stream which is fed by snow melt and small sprigs. The

stream flows from a narrow Canyon. The MHPP is made at the entrance of the

Canyon. The following Hydraulic structures present at the site.

Weir: a temporary weir is made. All the water of the stream is diverted to the

Headrace canal by simply putting some stones at the front of the stream.

Headrace canal: the headrace canal is an open earth channel which conveys

water from intake to the FBT .The length of the channel is 200 meter. A lot of

flow is lost due to leakages from the channel.

Spill way: a spillway is made near the weir i-e at the beginning of the

headrace canal.

FBT: a FBT is made at the end of headrace canal. The FBT is situated at

wrong position so a lot of head is lost.

Penstock: A locally made penstock of 30 inches diameter is installed at wrong

position to FBT. The penstock is not jointed well so a lot of water is lost on

the way. A trash rack is fixed at the opening of penstock .The trash rack is not

well designed.

Foundation for Impulse CFT turbine: an above ground type concrete

foundation for CFT is made.

Tailrace: the tailrace is an open channel which conveys water back to the

stream.

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CHAPTER 3

ELECTRO-MECHANICAL EQUIPMENT

3.1 HYDRAULIC TURBINES

Turbine is the main piece of equipment in the MHPP scheme that

converts energy of the falling water into the rotating shaft power. The selection of the

most suitable turbine for any particular hydro site depends mainly on two of the site

characteristics – head and flow available. All turbines have a power-speed

characteristic. This means they will operate most efficiently at a particular speed, head

and flow combination. Thus the desired running speed of the generator or the devices

being connected/ loading on to the turbine also influence selection. Other important

consideration is whether the turbine is expected to generate power at part-flow

conditions. The design speed of a turbine is largely determined by the head under

which it operates. Turbines can be classified as high head, medium head or low head

machines. They are also classified by the operating principle and can be either

impulse or reaction turbines. The basic turbine classification is given in the table

below:

Table 3.1 Turbine types

Type High Head Medium Head Low Head

Impulse turbines Pelton

Turgo

Cross-flow

Turgo

Multi-jet Pelton

Cross-flow

Reaction turbines - Francis Propeller

Kaplan

29

The potential energy in the water is converted into mechanical energy in the turbine,

by one of two fundamental and basically different mechanisms:

The water pressure can apply a force on the face of the runner blades, which

decreases as it proceeds through the turbine. Turbines that operate in this way

are called reaction turbines. The turbine casing, with the runner fully

immersed in water, must be strong enough to withstand the operating pressure.

The water pressure is converted into kinetic energy before entering the runner.

The kinetic energy is in the form of a high-speed jet that strikes the buckets,

mounted on the periphery of the runner. Turbines that operate in this way are

called impulse turbines. As the water after striking the buckets falls into the

tail water with little remaining energy, the casing can be light and serves the

purpose of preventing splashing.

3.2 IMPULSE TURBINES

Impulse turbines are more widely used for micro-hydro applications as

compared to reaction turbines because they have several advantages such as simple

design (no pressure seals around the shaft and better access to working parts - easier

to fabricate and maintain), greater tolerance towards sand and other particles in the

water, and better part-flow efficiencies. The impulse turbines are not suitable for low

head sites as they have lower specific speeds and to couple it to a standard alternator,

the speed would have to be increases to a great extent. The multi-jet Pelton, cross

flow and Turgo turbines are suitable for medium heads.

3.2.1 PELTON TURBINES

Pelton turbines are impulse turbines where one or more jets impinge on a

wheel carrying on its periphery a large number of buckets. Each jet issues through a

nozzle with a needle (or spear) valve to control the flow (figure 3.1). They are only

used for relatively high heads. The axes of the nozzles are in the plane of the runner to

stop the turbine. e.g. When the turbine approaches the runaway speed due to load

rejection- the jet may be deflected by a plate so that it does not impinge on the

buckets. In this way the needle valve can be closed very slowly, so that overpressure

surge in the pipeline is kept to an acceptable minimum. Any kinetic energy leaving

30

the runner is lost and so the buckets are designed to keep exit velocities to a

minimum. The turbine casing only needs to protect the surroundings against water

splashing and therefore can be very light.

Figure 3.1 Pelton runner

3.2.2 TURGO IMPULSE TURBINES

The Turgo turbine is an impulse turbine designed for medium head

applications. These turbines achieve operational efficiencies of up to 87%. Developed

in 1919 by Gilkes as a modification of the Pelton wheel, the Turgo has certain

advantages over Francis and Pelton designs for some applications. Firstly, the runner

is less expensive to make than a Pelton wheel while it does not need an airtight

housing like the Francis turbines. Finally the Turgo has higher specific speeds and at

the same time can handle greater quantum of flows than a Pelton wheel of the similar

diameter, leading to reduced generator and installation cost. Turgo turbines operate in

a head range where the Francis and Pelton overlap. Turgo installations are usually

preferred for small hydro schemes where low cost is very important.

Turgo turbine is an impulse turbine where water does not change pressure but

changes direction as it moves through the turbine blades. The water's potential energy

is converted to kinetic energy with a penstock and nozzle. The high speed water jet is

then directed on the turbine blades which deflect and reverse the flow and the water

exits with very little energy. Like all turbines with nozzles, blockage by debris must

31

be prevented for effective operation. A Turgo runner looks like a Pelton runner split

in half. For the same power, the Turgo runner is one half the diameter of the Pelton

runner, and so twice the specific speed. The Turgo can handle a greater water flow

than the Pelton because exiting water doesn't interfere with adjacent buckets.

Figure3.2 Turgo impulse turbine

3.2.3 CROSS FLOW TURBINE

Also called a Michell-Banki turbine a cross flow turbine has a drum-shaped

runner consisting of two parallel discs connected together near their rims by a series

of curved blades. A cross flow turbine always has its runner shaft horizontal (unlike

Pelton and Turgo turbines which can have either horizontal or vertical shaft

orientation). Unlike most water turbines, which have axial or radial flows, in a CFT

the water passes through the turbine transversely, or across the turbine blades. As with

a waterwheel, water enters at the turbine's edge. After passing the runner, it leaves on

the opposite side. Going through the runner twice provides additional efficiency.

When the water leaves the runner, it also helps clean the runner of small debris and

pollution. The cross-flow turbines generally operate at low speed.

32

Figure 3.3 CFT

CFTs are also often constructed as two turbines of different capacity that share

the same shaft. The turbine wheels are the same diameter, but different lengths to

handle different volumes at the same pressure. The subdivided wheels are usually

built with volumes in ratios of 1:2. The subdivided regulating unit (the guide vane

system in the turbine's upstream section) provides flexible operation, with ⅓, ⅔ or

100% output, depending on the flow. Low operating costs are obtained with the

turbine's relatively simple construction. The water flows through the blade channels in

two directions: outside to inside, and inside to outside. Most turbines are run with two

jets, arranged so that the two water jets in the runner will not affect each other. It is,

however, essential that the turbine, head and turbine speed are harmonized. The

turbine consists of a cylindrical water wheel or runner with a horizontal shaft,

composed of numerous blades (up to 37), arranged radially and tangentially. The edge

of the blades is sharpened to reduce resistance to the flow of water. A blade is made in

a part-circular cross-section (pipe cut over its whole length). The ends of the blades

are welded to disks to form a cage like a hamster cage and are sometimes called

"squirrel cage turbines"; instead of the bars, the turbine has trough-shaped steel

blades.

33

Figure 3.4 Horizontal/vertical inflows in CFT

The water flows first from the outside of the turbine to its inside. The

regulating unit, shaped like a vane or tongue, varies the cross-section of the flow.

These divide and direct the flow so that the water enters the runner smoothly for any

width of opening. The guide vanes should seal to the edges of the turbine casing so

that when the water is low, they can shut off the water supply. The guide vanes

therefore act as the valves between the penstock and turbine. The water jet is directed

towards the cylindrical runner by a fixed nozzle. The water enters the runner at an

angle of about 45 degrees, transmitting some of the water's kinetic energy to the

active cylindrical blades. The turbine geometry (nozzle-runner-shaft) assures that the

water jet is effective. The water acts on the runner twice, but most of the power is

transferred on the first pass, when the water enters the runner. Only ⅓ of the power is

transferred to the runner when the water is leaving the turbine.

The cross-flow turbine is of the impulse type, so the pressure remains constant

at the runner. The peak efficiency of a CFT is somewhat less than a Kaplan, Francis

or Pelton turbine. However, the CFT has a flat efficiency curve under varying load.

With a split runner and turbine chamber, the turbine maintains its efficiency while the

flow and load vary from 1/6th to the maximum.

The CFTs are mostly used in mini and micro hydropower units less than 2

MW and with heads less than 200 m, since it has a low price and good regulation.

Particularly with small run-of-the-river schemes, the flat efficiency curve yields better

performance than other turbine systems, as flow in small streams varies seasonally.

The efficiency of a turbine is determined whether electricity is produced during the

periods when rivers have low heads. Due to its better performance even at partial

loads, the CFT is well-suited to stand-alone electricity generation. It is simple in

construction and that makes it easier to repair and maintain than other turbine types.

34

Another advantage is that the CFTs gets cleaned as the water leaves the runner

(small sand particles, grass, leaves, etc. get washed away), preventing losses. So

although the turbine's efficiency is somewhat lower, it is more reliable than other

types. Other turbine types get clogged easily, and consequently face power losses

despite higher nominal efficiencies.

3.3 REACTION TURBINES

The more popular reaction turbines are the Francis turbine and the propeller

turbine. Kaplan turbine is a unique design of the propeller turbine. Given the same

head and flow conditions, reaction turbines rotate faster than impulse turbines. This

high specific speed makes it possible for a reaction turbine to be coupled directly to

an alternator without requiring a speed-increasing drive system. This specific feature

enables simplicity (less maintenance) and cost savings in the hydro scheme. The

Francis turbine is suitable for medium heads, while the propeller is more suitable for

low heads.

The reaction turbines require more sophisticated fabrication than impulse

turbines because they involve the use of larger and more intricately profiled blades

together with carefully profiled casings. The higher costs are often offset by high

efficiency and the advantages of high running speeds at low heads from relatively

compact machines. Expertise and precision required during fabrication make these

turbines less attractive for use in micro-hydro in developing countries. Most reaction

turbines tend to have poor part-flow efficiency characteristics.

3.3.1 FRANCIS TURBINES

The Francis turbine is a reaction turbine where water changes pressure as it moves

through the turbine, transferring its energy. A water tight casement is needed to

contain the water flow. Generally such turbines are suitable for sites such as dams

where they are located between the high pressure water source and the low pressure

water exit.

The inlet of a Francis turbine is spiral shaped. Guide vanes direct the water

tangentially to the turbine runner. This radial flow acts on the runner's vanes, causing

the runner to spin. The guide vanes (or wicket gate) are adjustable to allow efficient

turbine operation for a wide range of flow conditions. As the water moves through the

35

runner, it‟s spinning radius decreases, further delivering pressure acting on the runner.

This, in addition to the pressure within the water, is the basic principle on which the

Francis turbine operates. While exiting the turbine, water acts on cup shaped runner

buckets leaving without any turbulence or swirl and hence almost all of the kinetic or

potential energy is transferred. The turbine's exit tube is shaped to help decelerate the

water flow and recover the pressure.

Francis turbines can be designed for a wide range of heads and flows and

along with their high efficiency makes them one of the most widely used turbines in

the world. Large Francis turbines are usually designed specifically for each site so as

to gain highest levels of efficiencies (these are typically in the range of over 90%).

Francis turbines cover a wide range of head – from 20 meters to 700 meters, and can

be designed for outputs power ranging from just a few kilowatts to one Gig watt.

Figure 3.5 Francis Turbine

3.3.2 KAPLAN TURBINE

The Kaplan turbine has adjustable blades and was developed on the basic

platform (design principles) of the Francis turbine by the Viktor Kaplan in 1913. The

main advantage of Kaplan turbines is its ability to work in low head sites which was

36

not possible with Francis turbines. Kaplan turbines are widely used in high-flow, low-

head power production.

The Kaplan turbine is an inward flow reaction turbine, which means that the

working fluid changes pressure as it moves through the turbine and gives up its

energy. The design combines radial and axial features. The inlet is a scroll-shaped

tube that wraps around the turbine‟s wicket gate. Water is directed tangentially

through the wicket gate and spirals on to a propeller shaped runner, causing it to spin.

The outlet is a specially shaped draft tube that helps decelerate the water and recover

kinetic energy.

The turbine does not need to be at the lowest point of water flow, as long as the

draft tube remains full of water. A higher turbine location, however, increases the

suction that is imparted on the turbine blades by the draft tube that may lead to

cavitations due to the pressure drop. Typically the efficiencies achieved for Kaplan

turbine are over 90%, mainly due to the variable geometry of wicket gate and turbine

blades. This efficiency however may be lower for very low head applications. Since

the propeller blades are rotated by high-pressure hydraulic oil, a critical design

element of Kaplan turbine is to maintain a positive seal to prevent leakage of oil into

the waterway.

Kaplan turbines are widely used throughout the world for electrical power

production. They are especially suited for the low head hydro and high flow

conditions – mostly in canal based MHPP sites. Inexpensive micro turbines can be

manufactured for specific site conditions (e.g. for head as low one meter). Large

Kaplan turbines are individually designed for each site to operate at the highest

possible efficiency, typically over 90%. They are very expensive to design,

manufacture and install, but operate for decades.

Figure 3.6 Kaplan turbine

37

3.4 PUMPS WORKING AS TURBINES

Centrifugal pumps can be used as turbines by passing water through them in

reverse. The potential advantages are the lower costs due to mass production (also

local production), the availability of spare parts and the wider dealer/support

networks. The disadvantages are that their performance characteristics have not been

studied extensively and these poor part-flow efficiencies. Pumps as turbines have

been used at several locations but the technology still remains unproven.

3.5 TURBINE SELECTION

Selection of an appropriate turbine to a large extent is dependent upon the

available water head and to a lesser extent on the available flow rate. In general,

impulse turbines are used for high head sites, and reaction turbines are used for low

head sites. Kaplan turbines with adjustable blade pitch are suitable for wide ranges of

flow or head conditions, since their peak efficiency can be achieved over a wide range

of flow conditions.

Small turbines (less than 10 MW) may have horizontal shafts and even fairly

large bulb-type turbines up to 100 MW or so may be horizontal. Very large Francis

and Kaplan machines usually have vertical shafts because this makes best use of the

available head, and makes installation of a generator more economical. Pelton

turbines may be installed either vertically or horizontally. Some impulse turbines use

multiple water jets per runner to increase specific speed and balance shaft thrust.

Turbine type, dimensions and design are basically governed by the following

criteria:

Net head

Range of discharges through the turbine

Rotational speed

Cavitations problems

Cost

3.5.1 NET AVAILABLE HEAD

The gross head is the vertical distance, between the water surface level at the

intake and at the tailrace for reaction turbines and the nozzle level for impulse

38

turbines. Once the gross head is known, the net head can be computed by simply

subtracting the losses along its path. The first criterion to take into account in the

turbines selection is the net head. Table 3.2 specifies for each turbine type its range of

operating heads. The table shows some overlapping, so that for a certain head several

types of turbines can be used.

Table 3.2 Range of Heads

Turbine type Head range in meters

Kaplan and propeller 2 < H < 40

Francis 10 < H < 350

Pelton 50 < H < 1300

Michell-Benki 3 < H < 250

Turgo 50 < H < 250

The selection is particularly critical in low-head schemes, where to be

profitable large discharges must be handled. When contemplating schemes with a

head between 2 and 5 m, and a discharge between 10 and 100m3/sec, runners with

1.6-3.2 meters diameter are required, coupled through a speed increaser to an

asynchronous generator. The hydraulic conduits in general and water intakes in

particular are very large and require very large civil works, with a cost that generally

exceeds the cost of the electromechanical equipment.

In order to reduce the overall cost (civil works plus equipment) and more

specifically the cost of the civil works, several configurations, nowadays considered

as classic, have been devised. All of them include the only turbine type available for

this job .the Kaplan- in a double or a single regulated version.

The selection criteria for such turbines are well known:

Range of discharges

Net head

Geomorphology of the terrain

Environmental requirements (both visual and sonic)

Labor cost

The configurations differ by how the flow goes through the turbine (axial, radial, or

mixed) the turbine closing system (gate or siphon), the speed increaser type (parallel

gears, right angle drive, epicycloidal gears).

39

As a turbine can only accept discharges between the nominal and the practical

minimum, it may be advantageous to install several smaller turbines instead of a one

large. The turbines would be sequentially started, so all of the turbines in operation

except one will operate at their nominal discharges and therefore will exhibit a higher

efficiency. Using two or three smaller turbines will mean a lower unit weight and

volume and will facilitate transport and assembly on the site. The rotational speed of a

turbine is inversely proportional to its diameter, so its torque will be lower and the

speed increaser smaller and more reliable. The use of several turbines instead of one

large one with the same total power will result in a lower ratio kilogram of

turbine/cubic meter of operating flow, although the ratio equipment cost / cubic meter

of operating flow will be larger. Increasing the number of turbines decreases the

diameter of their runners, and consequently the support components in the

powerhouse will be smaller and lighter. As the water conduits are identical the

formwork, usually rather sophisticated, can be reused several times decreasing its

influence in the concrete cost. Notwithstanding this, generally more turbines means

more generators, more controls, higher costs.

3.5.2 DISCHARGE

The rated flow and net head determine the set of turbine types applicable to

the site and the flow environment. Suitable turbines are those for which the given

rated flow and net head plot within the operational envelopes. A point defined as

above by the flow and the head will usually plot within several of these envelopes. All

of those turbines are appropriate for the job, and it will be necessary to compute

installed power and electricity output against costs before taking a decision. It should

be remembered that the envelopes vary from manufacturer to manufacturer and they

should be considered only as a guide.

40

Table 3.3 Turbine Application Chart

3.5.3 SPECIFIC SPEED

Turbine type needs to be selected in consideration of the specific speed and

turbine characteristics. The specific speed, which is the important factor to select

turbine type, is defined as following formula.

3.1

Where,

Ns: Specific speed [m-kW]

N: Rotation speed [min-1]

P: Turbine output [kW]

H: Effective head [m]

The proper range of the specific speed has already been known as shown in

Table 3.4.The rotation speed of the turbine is limited. Therefore, it should be checked

whether the specific speed is within the proper range. The larger the rotation speed is,

the smaller the equipment is. The small equipment shall reduce the equipment cost. In

addition, the rotation speed affects draft head.

41

Table 3.4 Range of Ns

Turbine type Range of Ns(m-kW)

Pelton 8-25

Francis 50-350

Diagonal flow 100-350

Propeller 200-900

Tubular More than 500

3.5.4 CAVITATION

When the hydrodynamic pressure in a liquid flow falls below the vapor

pressure of the liquid, there is a formation of the vapour phase. This phenomenon

induces the formation of small individual bubbles that are carried out of the low-

pressure region by the flow and collapse in regions of higher pressure. The formation

of these bubbles and their subsequent collapse gives rise to what is called cavitations.

Experience shows that these collapsing bubbles create very high impulse pressures

accompanied by substantial noise (in fact a turbine undergoing cavitations sounds as

though gravel is passing through it). The repetitive action of such pressure waves

close to the liquid-solid boundary results in pitting of the material. With time this

pitting degenerates into cracks formed between the pits and the metal is spilled from

the surface. In a relatively short time the turbine is severely damaged and will require

being shut-off and repaired If possible.

Experience shows that there is a coefficient, called Thomas sigma, which defines

precisely enough under which parameters cavitations takes place.

This coefficient is given by the equation

3.2

Where

Hsv is the net positive suction head and H the net head of the scheme

3.3

Where,

Hsv is the net positive suction head

Hatm is the atmospheric pressure head

42

Hatm is the water vapor pressure

Z is the elevation above the tail water surface of the critical location

Ve is the average velocity in the tailrace

Hl is the head loss in the draft tube

Neglecting the draft-tube losses and the exit velocity head loss,

Thomas sigma will be given by

3.4

To avoid cavitations the turbine should be installed at least at a height over the

tailrace water level Zp given by the equation

3.5

The Thomas sigma is usually obtained by a model test, and it is a value furnished by

the turbine manufacturer. Notwithstanding the above mentioned statistic studies also

relates Thomas sigma with the specific speed. There under are specified the equation

giving óT as a function of ns for the Francis and Kaplan turbines

It must be remarked that Hvap decreases with the altitude, from roughly 10.3 m at the

sea level to 6.6 m at 3000 m above sea level. So then a Francis turbine with a specific

speed of 150, working under a 100 m head (with a corresponding óT = 0.088), that in

a plant at sea level, will require a setting:

z = 10.3 - 0.09 - 0.088 x 100 = 1.41 m

Installed in a plant at 2000 m above the sea level will require

z = 8.1-0.09 - 0.088 x 100 = -0.79 m

A setting requiring heavy excavation

3.5.5 ROTATIONAL SPEED

The rotational speed of a turbine is a function of its specific speed, and of the

scheme power and net head. In the small hydro schemes standard generators should

be installed when possible, so in the turbine selection it must be borne in mind that the

turbine, either coupled directly or through a speed increaser, should reach the

synchronous speed, as given in table 3.5

43

Table 3.5 Generator synchronization speed

3.5.6 RUNAWAY SPEED

Each runner profile is characterized by a maximum runaway speed. This is the

speed, which the unit can theoretically attain when the hydraulic power is at its

maximum and the electrical load has become disconnected. Depending on the type of

turbine, it can attain 2 or 3 times the nominal speed. Table 3.6 shows this ratio for

conventional and unconventional turbines.

It must be remembered that the cost of both generator and gearbox may be increased

when the runaway speed is higher, since they must be designed to withstand it.

Table 3.6 Turbine runaway speed

3.6 DRIVE SYSTEM

In order to generate electrical power at a stable voltage and frequency, the

drive system needs to transmit power from the turbine to the generator shaft in the

required direction and at the required speed. Typical drive systems in micro-

hydropower systems are as follows:

• Direct drive: A direct drive system is one in which the turbine shaft is connected

directly to the generator shaft. Direct drive systems are used only for cases where the

44

shaft speed of the generator shaft and the speed of the turbine are compatible. The

advantages of this type of system are low maintenance, high efficiency and low cost.

• “V” or wedge belts and pulleys: This is the most common choice for micro-

hydropower systems. Belts for this type of system are widely available because they

are used extensively in all kinds of small industrial machinery.

• Timing belt and sprocket pulley: These drives are common on vehicle camshaft

drives and use toothed belts and pulleys. They are efficient and clean-running and are

especially worth considering for use in very small system drives (less than 3 kW)

where efficiency is critical.

• Gearbox: Gearboxes are suitable for use with larger machines when belt drives

would be too cumbersome and inefficient. Gearboxes have problems regarding

specification, alignment, maintenance and cost, and this rules them out for micro-

hydropower systems except where they are specified as part of a turbine-generator set.

3.7 GENRATOR

Generators transform mechanical energy into electrical energy. Although most

early hydroelectric systems were of the direct current variety to match early

commercial electrical systems, nowadays only three-phase alternating current

generators are used in normal practice. Two types of current are produced by

electrical generators, either alternating current (AC) or direct current (DC). In the case

of AC the voltage cycles sinusoidally with time, from positive peak value to negative.

Because the voltage changes its sign the resulting current also continually reverses

direction in a cyclic pattern. DC current flows in a single direction as the result of a

steady voltage. DC is not usually used in modern power installations except for very

low-powered systems of a few hundred watts or less.

Alternating voltage can be produced in a stationery coil or armature by a

rotating magnetic field, but more usually a coil is rotated in a stationary magnetic

field. The magnetic field can be produced either by a permanent magnet or by another

coil (i.e., an electro-magnet) know as a field coil which is fed by direct current known

as the excitation current. A generator supplying alternative current is described as an

alternator to distinguish it from a machine designed to supply DC current which is

known as a DC generator or dynamo. Current flows when a voltage difference is

place across a conducting body. In AC circuits the magnitude and timing of the

45

current cycle relative to the voltage cycle will depend on whether the conductivity

body is resistance, inductive, capacitive or some combination of these elements.

3.7.1 SYNCHRONOUS GENRATOR

Synchronous generators equipped with a DC excitation system (rotating or

static) associated with a voltage regulator, to provide voltage, frequency and phase

angle control before the generator is connected the reactive energy required by the

power system when the generator is tied into the grid. Synchronous generators are

more expensive than asynchronous generators and are used in power systems where

the output of the generator represents a substantial proportion of the power system

load.

The synchronous generator is started before connecting it to the mains by the

turbine rotation. By gradually accelerating the turbine the generator is synchronized

with the mains, regulating the voltage, frequency and rotating sense, When the

generator reaches a velocity close to synchronous, the exciter regulates its field coils

current so the generator voltage is identical to the mains voltage. When the

synchronous generator is connected to an isolated net, the voltage controller maintains

a predefined constant voltage, independent of the load. If it is connected to the main

supply, the controller maintains the reactive power at a predefined level.

3.7.2 ASYNCHRONOUS GENRATOR

Asynchronous generators are simple squirrel-cage induction motors with no

possibility of voltage regulation and running at a speed directly related to system

frequency. They draw their excitation current from the grid, absorbing reactive energy

by their own magnetism. Adding a bank of capacitors can compensate for the

absorbed reactive energy. They cannot generate when disconnected from the grid

because are incapable of providing their own excitation current. Asynchronous

generators are cheaper and are used in large grids where their output is an

insignificant proportion of the power system load. Their efficiency is 2 to 4 per cent

lower than the efficiency of synchronous generators over the entire operating range.

In general, when the power exceeds 5000 kVA a synchronous generator is installed.

An asynchronous generator needs to absorb a certain power from the three phase

mains supply to ensure its magnetization even, if in theory, the generator can receive

46

its reactive power from a separate source such as a bank of capacitors. The mains

supply defines the frequency of the stator rotating flux and hence the synchronous

speed above which the rotor shaft must be driven. On start-up, the turbine is

accelerated up to 90-95% of the synchronous speed of the generator, when a velocity

relay closes the main line switch. The generator passes immediately to hyper-

synchronism and the driving and resisting torque are balanced in the area of stable

operation.

3.7.3 EXCITERS

The exciting current for the synchronous generator can be supplied by a small

DC generator, known as the exciter, to be driven from the main shaft. The power

absorbed by this dc generator amounts to 0.5% - 1.0% of the total generator power.

Nowadays a static exciter usually replaces the DC generator, but there are still many

rotating exciters in operation.

Rotating exciters: The field coils of both the main generator and the exciter

generator are usually mounted on the main shaft. In larger generators a pilot

exciter is also used. The pilot exciter can be started from its residual magnetic

field and it then supplies the exciting current to the main exciter, which in turn

supplies the exciting current for the rotor of the generator. In such way the

current regulation takes place in the smaller machine.

Brushless exciters: A small generator has its field coils on the stator and

generates AC current in the rotor windings. A solid state rectifier rotates with

the shaft, converting the AC output from the small generator into the DC

which is the supplied to the rotating field coils of the main generator without

the need of brushes. The voltage regulation is achieved by controlling the

current in the field coils of the small generator.

Static exciters: The exciting current is taken out, via a transformer, from the

output terminals of the main generator. This AC current is then rectified in a

solid state rectifier and injected in the generator field coils. When the

generator is started there is no current flowing through the generator field

coils. The residual magnetic field, aided if needed by a battery, permits

generation to start to be then stabilized when the voltage at the generator

terminals reaches a preset value. This equipment is easy to maintain has a

47

good efficiency and the response to the generator voltage oscillations is very

good.

3.8 TURBINE CONTROL

Turbines are designed for a certain net head and discharge. Any deviation

from these parameters must be compensated for, by opening or closing control

devices such as the wicket-vanes or gate valves to keep constant, either the outlet

power, the level of the water surface in the intake or the turbine discharge.

In schemes connected to an isolated net, the parameter to be controlled is the

runner speed, which controls the frequency. The generator becomes overloaded and

the turbine slows-down. In this case there are basically two approaches to control the

runner speed: either by controlling the water flow to the turbine or by keeping the

water flow constant and adjusting the electric load by an electric ballast load

connected to the generator terminals.

In the first approach, speed (frequency) regulation is normally accomplished

through flow control; once a gate opening is calculated, the actuator gives the

necessary instruction to the servomotor, which results in an extension or retraction of

the servo‟s rod. To ensure that the rod actually reaches the calculated position,

feedback is provided to the electronic actuator. These devices are called .speed

governors.

In the second approach it is assumed that, at full load, constant head and flow,

the turbine will operate at design speed, so maintaining full load from the generator;

this will run at a constant speed. If the load decreases the turbine will tend to increase

its speed. An electronic sensor, measuring the frequency, detects the deviation and a

reliable and inexpensive electronic load governor, switches on preset resistances and

so maintains the system frequency accurately.

The controllers that follow the first approach do not have any power limit. The

Electronic Load Governors, working according to the second approach rarely exceeds

100 kW capacities.

48

3.8.1 SPEED GOVERNORS

A governor is a combination of devices and mechanisms, which detect speed

deviation and convert it into a change in servomotor position. A speed-sensing

element detects the deviation from the set point; this deviation signal is converted and

amplified to excite an actuator, hydraulic or electric, that controls the water flow to

the turbine. In a Francis turbine, where to reduce the water flow you need to rotate the

wicket-gates a powerful governor is required to overcome the hydraulic and frictional

forces and to maintain the wicket-gates in a partially closed position or to close them

completely. Several types of governors are available varying from purely mechanical

to mechanical hydraulic to electro hydraulic. The purely mechanical governor is used

with fairly small turbines, because its control valve is easy to operate and does not

require a big effort. These governors use a fly ball mass mechanism driven by the

turbine shaft. The output from this device .the fly ball axis descends or ascends

according to the turbine speed- directly drive the valve located at the entrance to the

turbine.

Figure 3.7 Oil – Pressure Governor

49

The most commonly-used type is the oil-pressure governor (Fig 3.7) that also

uses a fly ball mechanism lighter and more precise than that used in a purely

mechanical governor. When the turbine is overloaded, the fly balls slowdown, the

balls drop, and the sleeve of the pilot valve rise to open access to the upper chamber

of the servomotor. The oil under pressure enters the upper chamber of the servomotor

to rotate the wicket-gates mechanism and increase the flow, and consequently the

rotational speed and the frequency.

In an electro hydraulic governor a sensor located on the generator shaft

continuously senses the turbine speed. The input is fed into a summing junction,

where it is compared to a speed reference. If the speed sensor signal differs from the

reference signal, it emits an error signal (positive or negative) that, once amplified, is

sent to the servomotor so this can act in the required sense. In general the actuator is

powered by a hydraulic power unit consisting of a sump for oil storage, an electric

motor operated pump to supply high pressure oil to the system, an accumulator where

the oil under pressure is stored, oil control valves and a hydraulic cylinder. All these

regulation systems, as have been described, operate by continuously adjusting back

and forth the wicket-gates position. To provide quick and stable adjustment of the

wicket-gates, and/or of the runner blades, with the least amount of over or under

speed deviations during system changes a further device is needed. In oil pressure

governors, as may be seen in figure 3.7, this is achieved by interposing a .dash pot.

that delays the opening of the pilot valve. In electro hydraulic governors the degree of

sophistication is much greater, so that the adjustment can be proportional, integral and

derivative (PID) giving a minimum variation in the controlling process.

An asynchronous generator connected to a large net, from which it takes its

reactive power to generate its own magnetism, does not need any controller, because

its frequency is controlled by the mains. Notwithstanding this, when the generator is

disconnected from the mains the turbine accelerates up to runaway speed with

inherent danger for the generator and the speed increaser, if one is used. In such a case

it is necessary to interrupt the water flow, rapidly enough to prevent the turbine

accelerating, but at the same time minimizing any water hammer effect in the

penstock.

To ensure the control of the turbine speed by regulating the water flow,

certain inertia of the rotating components is required. Additional inertia can be

provided by a flywheel on the turbine or generator shaft. When the main switch

50

disconnects the generator the power excess accelerates the flywheel; later, when the

switch reconnects the load, the deceleration of this inertia flywheel supplies additional

power that helps to minimize speed variation. The basic equation of the rotating

system is the following:

3.6

Where,

J = moment of inertia of the rotating components

W = angular velocity

Tt = torque of turbine

TL= torque due to load

When Tt is equal to TL, dW/dt = 0 and W = constant, so the operation is steady.

When Tt is greater or smaller than TL, W is not constant and the governor must

intervene so that the turbine output matches the generator load. But it should not be

forgotten that the control of the water flow introduces a new factor: the speed

variations on the water column formed by the waterways.

The flywheel effect of the rotating components is stabilizing whereas the water

column effect is destabilizing. The start-up time of the rotating system, the time

required to accelerate the unit from zero rotational speed to operating speed is given

by

3.7

Where the rotating inertia of the unit is given by the weight of all rotating parts

multiplied by the square of the radius of gyration: WR2, P is the rated power in Kw

and n the turbine speed (rpm)

The water starting time, needed to accelerate the water column from zero velocity to

some other velocity V, at a constant head H is given by:

3.8

51

Where,

H = gross head across the turbine (m)

L = length of water column (m)

V = velocity of the water (m/s)

g = gravitational constant (9.81 m s-2)

To achieve good regulation is necessary that Tm/Tw > 4. Realistic water starting

times do not exceed 2.5 sec. If it is larger, modification of the water conduits must be

considered either by decreasing the velocity or the length of the conduits by installing

a surge tank. The possibility of adding a flywheel to the generator to increase the

inertia rotating parts can also considered. It should be noted that an increase of the

inertia of the rotating parts will improve the water hammer effect and decrease the

runaway speed.

3.9 ELECTRO-MECHANICAL COMPONENTS OVER

THE SITE

The electro-mechanical structures present at the site are:

Cross flow turbine: A 10 kw cross flow turbine is installed. The turbine is an

old design version having no such design specification merely manufactured

on experience based by local manufacturer in Gujaro Gari(Mardan).

Generator: A 10 kw AC Synchronous generator is used to generate electric

power for lighting purposes only.

Flour Mill: a grinding machine (flour Mill) working when there is no need of

light during day time.

Pulley and Belt arrangement: V belt is used to connect turbine with

generator and flat belt is used in flour mill.

`

52

CHAPTER 4

SITE POTENTIAL AND FEASIBILITY STUDY

4.1 POTENTIAL SITE IDENTIFICATION

For efficient study, it is necessary to roughly examine whether or not the

construction of a hydropower plant in the target area (or near the power demand area)

is feasible. The best geographical areas for micro-hydropower systems are those

where there are steep rivers, streams, creeks or springs flowing year-round, such as in

hilly areas with high year-round rainfall. How much power capacity can be generated

sufficiently, before conducting field investigation? The initial examination is basically

a desk study using available reference materials and information and the basic steps of

the potential site identification is show in Figure 4.1

Figure 4.1 Step of Potential Site Identification

53

4.2 FEASIBILITY STUDY

A pre-feasibility study is carried out to determine whether the site is worth

further investigation. This study could involve visiting a site to measure head and

flow rate, or it could simply be a map study. If the site looks promising, the next step

is to carry out a full-scale, detailed feasibility study. Information collected by this

study should be of the highest quality and should be accurate enough to permit a full

technical design of the project without further visit. A feasibility study includes a site

survey and investigation, a hydrological assessment, an environmental assessment, the

project design, a detailed cost estimate and the final report. The depth of study will

depend largely on the size and complexity of the system. For a small system such as a

battery-based system, the feasibility study can be less rigorous than for a larger

system.

Carrying out a feasibility study is highly technical. Unless one has a strong

background and experience in the area, it is best left to professional consultants or

energy experts.

Figure 4.2 Micro hydro Development Flow chart

54

4.3 PRELIMINARY SITE SURVEY

The objective of preliminary site survey for micro-hydro is to investigate a

potential site and supply area in order to roughly evaluate the feasibility of projects

and get information on electrification planning around the site in the case of off-grid

project or existing transmission facilities (and/or planned transmission line) to be

interconnected in the case of on-grid project. One of the most important activities in

preliminary site survey is to measure water discharge and head that could be utilized

for micro/small-hydropower generation. Investigations of intake site, waterway route,

powerhouse site and transmission route etc. are also conducted to assess the feasibility

of project sites. In the case of off-grid project, power demand survey is also important

in the planning of the electrification system. Socio-economic data such as number of

households and public facilities in supply area, availability of local industries which

will use electricity, solvency of local people for electricity and the acceptability of

local people to the electrification scheme are gathered during the preliminary site

survey.

Basic items to be investigated in a preliminary site survey are:

Potential capacity of the project site

Measurement of river flow

Measurement of head

Topographical and geological condition of the sites for the structure layout

Accessibility to the site

In the case of off-grid project:

Power demand in the load center

Distance from the load center to the power house

Ability of the local people to pay for electricity

Willingness of the local people for electrification

In the case of on-grid project:

Distance from existing transmission facilities (and/or planned transmission

line) to the power house.

55

4.4 Survey to Outline the Project Site

During the reconnaissance at the proposed site of power generating facilities and

around the power demand area, a survey should be conducted on the following items:

4.4.1 ACCESS CONDITIONS

The equipment and machinery used for the construction and operation of a

micro hydropower plant are smaller and lighter than those used for an ordinary

hydropower plant and it may be possible in some cases that such equipment and

machinery can be brought to the site either manually or using simple vehicles. Given

the smaller capacity of the power generated by a micro/small-hydropower plant,

careful consideration is required in the use of transportation method and access other

than the use of an existing road or vehicle since the construction of a new access road

could be a factor that would considerably reduce the economy of a project. In the case

of a mountainous area, there may be an abandoned road (previously used for the

hauling of cut trees, etc.) which is difficult to find because it has been covered by

vegetation and it is important to interview local residents on the existence of such a

road.

4.4.2 SITUATION OF RIVER WATER UTILIZATION

The existence of facilities utilizing the river flow, the flow volume and any

relevant future plans regarding the river from which a planned micro/small-

hydropower plant will draw water should also be surveyed. At the project formulation

stage, the situation of the portion or section of the river for water utilization should be

surveyed taking into consideration the assumed recession section and the possibility

of changes in the position of the intake and the waterway route. When a fall or steep

valley is to be used for power generation, local information on the use of such a fall or

valley should be obtained together with a survey on the relevant legal regulations.

56

4.4.3 STRUCTURE SITE INVESTIGATION

Taking into account the requirements for structure layout, an investigation at

each facility site is conducted as follows;

(1) Intake site

To determine the approximate location of the weir and intake

To draw sketches and to take photographs

(2) Headrace

To measure the head and length of waterway route

To investigate the surrounding conditions

To draw sketches and/or to take photographs

Photographs of the site

(3) Forebay/Head tank and Penstock

To investigate the forebay site

Suitable location for the forebay site

Adequate space for construction

To investigate the penstock route

Length of the penstock measured with distance meter or measuring tape

Geological and topographical conditions

(4) Power house

To investigate the slope condition. Unstable slopes, such as landslides or

collapses behind the powerhouse site

To measure the approximate location

Head between forebay and powerhouse measured with sight meter (hand-

level)and distance meter

To investigate the land use conditions, Location of artificial structures near the

powerhouse site, if any

To investigate tailrace route

Location of tailrace outlet

Length of tailrace measured with a measuring tape

To take photographs and draw sketches

57

(5) Transmission/Distribution Line

To survey the geological and topographical conditions from the powerhouse

site to the load center

To select a transmission line along existing road or foot path

To measure the length of the transmission route

To trace transmission line on maps

To take photographs and draw sketches of powerhouse site

4.5 FLOW DATA

Flow rate is the quantity of water available in stream or river and may vary

widely over the course of a day, week, month and year. In order to adequately assess

the minimum continuous power output to be expected from the micro-hydropower

system, the minimum quantity of water available must be determined. The purpose of

a hydrology study is to predict the variation in the flow during the year. It is important

to know the mean stream flow and the extreme high- and low-flow rates. Whenever

possible, stream flow data should be measured daily and recorded for at least one

year; two to three years is ideal. If not, a few measurements should be made during

the low flow season. If you are familiar with the stream, you might determine the low-

flow season by keeping track of water levels and making several flow measurements

for more than a week when the water level is at its lowest point during the year.

Information could be obtained from neighbors or other sources.

There are a variety of techniques for measuring stream flow rate; the most commonly

used are;

Container method

Float method

Weir method

Current meter method

4.5.1 CONTAINER METHOD

For very small streams, a common method for measuring flow is the container

method. This involves diverting the whole flow into a container such as a bucket or

barrel by damming the stream and recording the time it takes for the container to fill.

58

The rate that the container fills is the flow rate, which is calculated simply by dividing

the volume of the container by the filling time. Flows of up to20 LPs can be measured

using a 200-litre container such as an oil drum.

Figure 4.3 Flow measuring container method

4.5.2 WEIR METHOD

A weir is a structure such as a low wall across a stream. A flow measurement

weir has a notch through which all water in the stream flows. The flow rate can be

determined from a single reading of the difference in height between the upstream

water level and the bottom of the notch. For reliable results, the crest of the weir must

be kept sharp, and sediment must be prevented from accumulating behind the weir.

Weirs can be timber, concrete or metal and must always be oriented at a right angle to

the stream flow. The weir should be located at a point where the stream is straight and

free from eddies. It is necessary to estimate the range of flows to be measured before

designing the weir in order to ensure that the chosen size of notch will be adequate to

pass the magnitude of the stream flow. Rectangular weirs are more suitable for large

flows in the range of 1000 LPs, and triangular weirs are suitable for small flows that

have wide variation. A combination triangular/rectangular compound weir may be

incorporated into one weir to measure higher flows; at lower flows the water goes

through the triangular notch.

59

Figure 4.4 flow measuring weir method

4.5.3 FLOAT METHOD

Float method of finding flow rate required the following steps

1. Measure the speed of the water (in feet per second)

2. Determine the cross-sectional area of the water source (in square feet) by

measuring and multiplying the average water depth (in feet) X the average

water width (in feet)

3. Calculate the flow (in cubic feet per second) by multiplying the water speed X

the cross-sectional area.

Water Speed

Determining the water speed is easy. Pick a representative segment of river or

stream close to the expected water diversion point. Place two stakes 50 feet apart

along the bank, marking the upper and lower limits of this segment. Drop a Ping-Pong

ball (or other lightweight, floating object) into the current opposite the upper stake.

Time (a wrist watch with a second hand works great!) how long it takes for the Ping-

Pong ball to travel the 50feet. Take this measurement several times and calculate the

average time (add all times and divide by the number of trials). This is the speed of

the water through the segment at the surface. Not all water moves as fast as the

surface because there is friction at the bottom and along the banks. This velocity must

60

then be reduced by correction factor, which estimates the mean velocity as opposed to

the surface velocity. By multiplying averaged and corrected flow velocity, the volume

flow rate is estimated. This method provides only an approximate estimate of the

flow. Approximate correction factors to convert measured surface velocity to mean

velocity are as follows:

Table 4.1 stream friction correction factor (n)

Stream Type Fraction Factor (n)

Concrete channel,rectangular,smooth 0.85

Large,slow,clear stream 0.75

small,slow,clear stream 0.65

Shallow(less than 0.5m/1.5ft.) turbulent

stream

0.45

Very shallow rocky stream 0.25

Cross-Sectional Area

Now we can measure and calculate the cross-sectional area of a „slice‟ of the

water. In the segment used above for determining water speed, select a spot that will

provide a representative water depth and width for the 50 ft. segment. Measure and

record the water depth at one foot increments along a cross section (water-edge to

water-edge) of the river or stream at this spot. Laying a log or plank across the river or

stream from which you can take these measurements is convenient. You can also

wade (or boat) across but take care that you are measuring the actual water depth and

not the depth of water affected by your presence in the water. Calculate the average

depth of the water (as explained above during water speed).Measure and record the

width of the river or stream (in feet and from water-edge to water edge).Multiply the

average depth X the width. You now have the cross-sectional area (in square feet) of

that „slice‟ of the river or stream.

61

Figure 4.5 flow measuring Float method

Calculating Flow

The following equation is used to calculate Flow.

Water Speed (ft/sec) X Cross Sectional Area (sq ft) =Flow (cubic feet per second) X

450 = Flow (gallons per minute)

Calculate the flow in cubic feet/second first by multiplying the average speed (in feet

per second) X the cross-sectional area (in square feet). Then convert the flow from

cubic feet per second to gallons per minute (GPM) by multiplying the cubic feet per

second X 450.

4.6 MEASUREMENT OF HEAD

The head between the intake point and the head tank and the head between the

head tank and the outlet point should be measured. At the initial planning stage,

however, it may be sufficient to measure the head between the planned head tank

location and the outlet level. While a surveying level can be used for the purpose of

measuring, a more simple head measuring method may be sufficient. The followings

are simple methods of head measurement.

62

4.6.1 CLEAR HOSE METHOD

The figure below shows this method. The method is useful for low head sites,

since it is cheap and reasonably accurate. To get the head of two points, measure the

difference of water level of the water-filled clear hose at two points. Even a man who

does not have a skill of survey work can apply this method.

Figure 4.6 Head measuring clear hose method

4.6.2 SPIRIT LEVEL AND PLANK METHOD

Below figure shows the principle of this method. A horizontal sighting is

established by a carpenter‟s spirit level placed on a reliably straight and inflexible

plank of wood. A method simpler than this is named Pole survey. The Pole survey

method is a tape measure is used instead of a wooden plank and a spirit level, a

leveling rod is fixed perpendicularly, and then a tape measure is moved up and down

along with a leveling rod. The reading value of a leveling rod of the position which

reading value of a tape measure decreases most is a height difference between points.

Figure4.7 Head measuring Plank Method

63

4.6.3 Sighting meter method

Hand-hold sighting meters measure angle of inclination of a slope (they are

often called clinometers or Abney levels). A head is calculated by the following

formula using a vertical angle that is measured by a hand-hold sighting meter, and a

hypotenuse distance measured by tape measure.

Ｈ＝Ｌ× sinθ

H: Head L: Hypotenuse distance θ: Vertical angle

Figure 4.8 Head measuring Sighting meter Method

4.7 FLOW &HEAD MEASUREMENT OVER THE SITE

4.7.1 FLOW RATE (DISCHARGE) MEASUREMENT

The flow rate in HRC is measured in two different positions i-e near the Weir

and at end the end of HRC. Float method is used for flow measurement.

Flow Rate(Q1) at the end of HRC:

First length for the float is mark up and measured ,

Total length (L1) = 48 ft (14.6304 meter)

Now width & Depth of the channel for the selected length is measured at different

position

W1 = 27 inches W3 = 26 inches W5 = 25.5 inches

W2 = 31 inches W4 = 25 inches W6 = 28 inches

Average value is calculated which is;

Wavg = 27.08 inches (0.6879meter)

64

And for average Depth (Davr):

D1 = 7 inches D3 = 7 inches D5 = 6 inches

D2 = 6.5 inches D4 = 5 inches

Therefore

Davg = 6.3 inches (0.16002meter)

Now Area (A1):

A1 = Davg × Wavg

A1 = 0.6879 × 0.16002

A1 = 0.11007 m2

Next step is to find the average time (Tavg) of the float to covered the marked distance

L1

T1 =14.97 sec T3 = 14.47 sec

T2 = 15 sec T4 = 14.55sec

Therefore

Tavg= 14.74 sec

Speed of flowing water is given by

V1 = L1/Tavg

V 1= 14.6304/14.74

V1 = 0.9920 meter/sec

So Flow Rate (Q1) is

Q1 = A1 × V1

Q1 = 0.11007 × 0.9920

Q1 = 0.1091 m3/sec

Q1 = 0.11m3/sec

Flow Rate (Q2) at the start of HRC:

The same method is repeated for finding flow rate at start of HRC.

Total length (L2) = 31 ft (9.448 meter)

Width & Depth of the channel for the selected length is measured at different

position

W1 = 31 inches W3 = 28.8 inches

W2 = 30 inches W4 = 29 inches

Therefore

Wavg = 29.7 inches (0.754meter)

65

And for average Depth (Davg):

D1 = 7 inches D3 = 6.2 inches D5 = 6.9 inches

D2 = 6.5 inches D4 = 5 inches

Therefore

Davr = 6.32 inches (0.160meter)

Now Area (A2):

A2 = Davg × Wavg

A2 = 0.160 × 0.754

A2 = 0.121 m2

Now we find the average time (Tavg) of the float to covered the measured distance L2

T1 =7.5 sec T3 = 9 sec T5 = 8 sec

T2 = 7 sec T4 = 8.5sec

Therefore

Tavrg= 8 sec

Speed of flowing water is given by

V2 = L2/Tavg

V 2= 9.448 /8

V1 = 1.1811 meter/sec

And the Flow Rate (Q2) is

Q2 = A2 × V2

Q2 = 0.121 × 1.1811

Q2 = 0.1429 m3/sec (actual discharge)

Loss of Flow Rate in HRC:

Q = Q2 – Q1

Q = 0.1429 – 0.1091

Q = 0.0338 m3/sec

4.7.2 HEAD MEASUREMENT

Clear Hose method has been used to measure the Available Head. In this

method the Head is measured in parts and is sum up. To get the head of two points,

measure the difference of water level of the water-filled clear hose at two points.

H1 = 88 inches H3 = 120 inches H5 = 90 inches

H2 = 96 inches H4 = 108 inches H6 = 84 inches

66

H = H1 + H2 + H3 + H4 + H5 + H6

H = 88 + 96 +120 +108 + 90 + 84

H = 586 inches (14.9 m)

Head loses: Due to wrong position of penstock with FBT

H1 = 88 inches (2.235m)

4.8 POWER CALCULATIONS

4.8.1 THEORETICAL POWER

Theoretical power of the of the site is

Pth = ρQHg

Pth = 1000 × 0.1429 × 14.9 × 9.8

Pth = 20.86 kw

4.8.2 ACTUAL POWER

Actual power output has been calculated by two ways:

Applying gradual load: In this method Load is applied and is increased

gradually. The actual power output is at that specific load at which the system

ceases. 1KW load was added one after the other through electric heater. So 4.5

KW was measured.

Finding out voltage and current at peak load: We find out voltage and

current at peak load.

V = 220 volts

I = 14.18 ampere

Pac = V × I × 0.84 × 3(1/2)

Pac = 220 × 14.18 × 3(1/2)

Pac = 4540 watt

Now Efficiency of the MHPPP is

η = ( Pac /Pth) ×100

η = (4.540/20.86) ×100

η = 21.76 %

67

4.8.3 POWER LOSSES

Power loses in HRC:

Plos = ρQHg

Plos = 1000 × 0.0338 × 14.9 × 9.8

P los = 4935 watts

Plos = 4.9 kw

Power loss due to head:

Plos = ρQHg

Plos = 1000 × 0.1429 × 2.235 × 9.8

Plos = 3.16 kw

Total power loss:

Plos/total = 4.9 + 3.16

Plos/tota = 8.06 kw

68

CHAPTER 5

RECOMMENDATIONS FOR ENHANCING

EFFICIENCY AND COST ESTIMATE

The calculated efficiency is 21% which is far below the optimum range 60-

75%. The much lower efficiency depicts serious shortcomings in the installed plant.

Careful calculations and analysis portray limitations in the following areas.

5.1 HEAD RACE CANAL

Losses in headrace canal are due to two reasons:

The HRC is an open earth channel (natural watercourse) so flow is turbulent in

the HRC which is due to level difference in the channel and zigzag path.

Excessive leakage from the Natural watercourse and reason is the same. The

approximate flow loss in the headrace canal due to leakage is 0.0338m3/sec.

The flow loss is calculated by measuring flow parameters near the weir and

FBT.

The turbulence and leakage in HRC could be avoided if

Efforts are made to align the natural water course straight with little bent-over.

Natural water course HRC is replaced with rectangular concrete channels with

spill ways in between and near FBT.

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5.2 WEIR

Weir is not properly designed and built since stones, wood logs and sands are

raw materials used. A medium level flow in rainy days could ruin the weir and it is

routine for the locals to built it again and again when flow in the stream increases.

To ensure stable flow even in rainy days, the weir must be made with concrete,

having steel fixers.

5.3 FOREBAY TANK

The purpose of FBT is to make flow laminar and to provide trash rack and

screens so that small pebbles and rocks couldn‟t get into penstock. The recent design

is illogical since the FBT is built almost 2.23m below the headrace canal without

leveling the upper part of FBT with HRC. The FBT never fills fully with water. And

hence almost 2.35m head loss occurs due to this.

The FBT would be purposeful if:

The upper level of the tank is aligned and leveled with HRC so that no head

loss occurs.

The penstock pipe which leads from the FBT to the turbine, must little bit

above the floor in order to get laminar flow. Another advantage of this

position is that the unwanted materials, pebbles, rocks etc would settle down

in the bottom, hence safe flow is ensured.

5.4 PENSTOCK It is the part which counts for almost 30% of the overall cost of the turbine.

The sizing is awesome i.e. having 30 inches diameter but little bit leakage is there

from penstock which requires minimal maintenance.

5.5 TURBINE Old version of cross flow turbine is installed. Major shortcomings are;

Excessive leakage due to large clearance volume between casing and rotor

blades.

Rough outer and interior periphery. Blades are not smoothly fabricated and

also the absence of well design trash rack and screens added more to this

misery.

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Inaccurate balding.

Excessive leakage from the nozzle

Absence of Draft tube

Difficulty in maintenance and cleaning due to complex assembly.

The old version of CFT must be replaced with the latest design cross flow

turbine having minimal clearance volume, sealing and fine blades. In the international

market, comparatively low cost and easily available choice would be T15 turbine

made by ENTEC. This firm has given license to manufacturers in Pakistan. Salient

features of the turbine are:

Welded Housing ,made of quality steel, rigid enough to withstand high

operational stress

Casing is designed in such a way to give flexibility regarding main bearings of

the runner, to cope with requirement like flywheel, built drive etc.

A sealing system( contact free or conventional type) is integrated in the slide

flanges. Guide vane unit could be easily taken out through slide flange for

cleaning maintenance.

Figure 5.1 T15 CFT

High precision fabrication of runner cylinder, laser cut slide disks and

exceptionally fine blading drawn from bright steel.

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Due to these salient features the organization claims efficiency of the turbine after

testing as:

Figure 5.2 T15 Efficiency after testing

The T15 turbine is available in Gujranwala, Lahore and Mardan.

5.6 ABSENCE OF AUTOMATIC CONTROL

Flow to the turbine is controlled via traditional manual valve i.e. If load

exceeds then the operator increases the flow and vice versa. The operator increases or

decreases flow via control valve observing voltmeter attached to the turbine but it is

very difficult to examine the flow 24\7. And the most reoccurring cost which the local

community is tired-of to pay, is the cost of blasted tube lights, which they almost

change once in two months approximately. The locals feel that they face two

problems:

Firstly when peak load exceeds then there is no mechanism to adjust that.

Secondly they are unable to control the instantaneous high voltage when there

is low load condition. Sudden rise and fall in voltage beyond optimum value,

cost heavily on poor people.

To cope with the problem, one should either install mechanical governor or

ELC (Electronic load controller). Practical experience depicts that mechanical

governor in MHPPPs often fails. So a viable alternative is ELC.

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An ELC is a solid-state electronic device designed to regulate output power of

a micro-hydropower system. Maintaining a near-constant load on the turbine

generates stable voltage and frequency. ELCs can also be used as a load-management

system by assigning a predetermined prioritized secondary load, such as water

heating, space heating or other loads. In this way, one can use the available power

rather than dumping it into the ballast load. Without an ELC, the frequency will vary

as the load changes and, under no-load conditions, will be much higher than rated

frequency. ELCs react so fast to load changes that speed changes are not even

noticeable unless a very large load is applied. The major benefit of ELCs is that they

have no moving parts, are reliable and are virtually maintenance-free. The advent of

ELCs has allowed the introduction of simple and efficient multi-jet turbines for

micro-hydropower systems that are no longer burdened by expensive hydraulic

governors.

Figure 5.3 Electronic Load Controller

There are various types of ELCs in the market that can regulate systems from

as small as 1 kW to 100 kW. The choice of the controller depends on the type of

generator you have. ELCs are suitable for synchronous generators. If there is an

induction generator, it will need an induction generator controller (IGC). IGCs work

on a principle that is similar to that used by ELCs, but an IGC monitors the generated

voltage and diverts the surplus power to the ballast load.

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5.7 LINE LOSSES

The line losses are due to the use of substandard cables and non-availability of

poles. Since the site is in mountainous territory, the cable is now and often passing

through large bulky trees. It is routine in raining that locals shut downs the plant since

the wooden pole or those wires which are passing through trees become short-

circuited. Poles with insulators for holding live wires are needed besides quality cable

for transmission

5.8 COST ESTIMATE

The power plant was installed in 2002 by the local community. The initial cost

(in rupees) of Electro-mechanical components and civil structures are as under:

Table 5.1 Initial cost estimate

On the basis of recommendations, two cost-plans are forecasted which are:

a. Plan-1 for NGOS and Govt. Organizations

b. Plan-2 for Local community

Penstock Pipe 57000

Turbine Accessories 50000

Dynamo1 30000

Line Cable 30000

Cement (23) 7000

Bricks 6000

Steel rods 27000

Bushes (3) 6000

Gate 1800

Pipe 3500

Concrete Blocks 2000

Labor Charges 15000

Miscellaneous 6840

Total Cost Rs. 212140

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a. Cost plan-1

In this plan our aim is to maximize the performance in optimum range of

expenditures. The old turbine must be replaced with T15 CFT. ELC is very much

important for smooth operation and to avoid failures of electrical appliances due to

extreme high and low peaks of voltage. The construction of FBT and headrace canal

is vital according to recommended design. The forecasted cost estimate is:

Table 5.2 Cost estimate for plane-1

Penstock (Installed) 0

15 KW T15 CFT with

accessories

600000

Civil Work 120000

ELC 400000

Labor Charges 30000

Total Rs. 1157000

Theoretical power output of the site is 21kw and installing 15KW T15 CFT, gives

5KW extra which was not harnessed previously. The efficiency of the plant could be

raised to its normal range which is 60-75%.

b. Plan-2:

In this plan, the aim is to minimize the overall expenditures as low as possible

in the optimum range of performance. The already installed old version of CFT could

be repaired. The nozzle at inlet to the turbine must be replaced because of excessive

leakage. The turbine blade angles must be checked and maintenance must be done to

smooth the periphery. The civil work is important and again a compromise is made on

ELC, since the price of ELC is very high in Pakistan. ELC could be installed in later

stage, if local manufacturers start producing ELC. It is of vital importance to

implement the recommended design of FBT and HRC, since both accounts for almost

50% power loss. The forecasted estimate is

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Table 5.3 Cost estimate for Plan-2

Repair of Installed CFT 10000

Nozzle Replacement 5000

Civil Work

(HRC +FBT)

100000

Labor work 25000

Total Rs. 140000

The efficiency of the already installed CFT could be improved almost 15%.

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References

Books

Fluid Mechanics, Hydraulics and Hydraulic Machines by Dr

K.R.ARORA

Manuals

How to Develop a small Hydro site by Layman

Micro-Hydro power: Reviewing an old concept by Butte, Montanna,

1979

A Guide to UK Mini Hydro Developments by British Hydro Power

Association

Micro hydro power systems, a buyer‟s Guide by Natural Resources

Canada

Research Papers

Best practices for sustainable development of Micro hydro power in

developing countries by Smail Khennas & Andrew Barnett

Understanding Micro hydro electric generation, Technical paper No 18

by weaver and Christopher s

Hydro power in the nineties (home power No 44) by Paul & Barbara

Small hydro power systems by NREL, U.S Department of Energy

Websites

www.microhydropower.net

www.minigrid.com

www.british-hydro.org

www.renewable-energy-sources.com

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Abbreviations:

MHPP = micro hydro power plant

CFT = Cross flow turbine

HRC = Head Race Canal

FBT = Fore bay tank

AC = alternating current

cfm = cubic feet per minute

DC = direct current

e = efficiency

ELC = electronic load controller

ft. = foot; feet

gpm = gallons per minute

Hz = hertz

IGC = induction generator controller

kW = kilowatt

kWh = kilowatt hour

lps = litres per second

m = metre

P = power

Q = flow rate

rpm = revolutions per minute

V = voltage

W = watt

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APPENDIX A

Measuring Channel Area HRC

FBT Weir

Measuring Available Head Penstock

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Spill way CFT

Electric CKT Flour Mill

Electric supply line Power House