Hydropower Engineering II

Chapter One
 Introduction
Definition:
 Hydropower engineering refers to the technology involved
in converting the pressure energy and kinetic energy of water
into more easily used electrical energy.
 The prime mover in the case of hydropower is a water wheel or
hydraulic turbine which transforms the energy of the water into
mechanical energy.
 Sources of water power?
 Hydroelectric Power Plant / Hydropower Plant
 Hydropower plants convert the potential energy of water (water falling over
a distance or head) into mechanical energy (rotation of the turbine shaft). This
shaft in turn is connected to the shaft of an electric generator to convert
mechanical energy into electrical energy.
 If the quantity of water available for the production
of power is designated as Q and the vertical distance
available is measured as H, the theoretical water
power due to a quantity of water (Q) falling H,

P=QρgH

where P - water power

Q – discharge
H – head
 Hydropower Plant Component Parts
 To generate electric power from water, three basic elements are necessary
1. A means of creating head: Dams, reservoirs
2. A means for conveying water from dam to turbine
• Headrace,
• Forbay,
• Intake: directs water from reservoir to penstock/power conduit
• Penstock: pressurized conduit conveying water to turbines
• Draft tube:
• Tail race:
3. A power plant: power house to generate electric power
• Turbines: converts potential and kinetic energy of the water to
mechanical energy
• Generators: converts mechanical energy to electrical energy
 Storage type Hydroelectric Power Plant

2
Draft Tube
Diversion type Hydroelectric Power Plant

`
POWER HOUSE

Hydraulic turbines:
converts water energy to
mechanical energy;

Generators:
Converts mechanical energy to
electrical energy
 Hydropower Development Cycle
Project Cycle
 Three project phases

Project
Project Planning Project Implementation
Operation

Design Review &

Feasibility Study
Modifications

Prefeasibility Study Contract Management and Construction

Supervision Works

Reconnaissance Procurement Construction Commissioning Full

Study Operation

10 - 15 years 2-10 years 50-100 years

Project Planning Phase
 Three stages

Feasibility Study One/two

2
Stage Alternatives

Prefeasibility 2 Few
5
Study Stage Alternatives

Reconnaissance Several
1 2 3 4 5
Study Stage Alternatives
 Hydropower
 The studies to be carried out are:
Development Cycles
 Resources studies
 Preparation/updating of resources inventories
 Preparation/updating of resources rankings
 Site specific studies
 Preliminary reconnaissance studies
 Pre-feasibility studies
 Feasibility studies
 The main purpose of resource inventory investigation is to identify, register and catalogue the
hydropower resource existing in a river basins; areas; districts and provinces.
 Basic Investigations: Having no established development purpose
 Purpose oriented Investigations: Carried out for specific purposes, i.e. in order to
meet identified needs
 Flow data and data on topography is sufficient to establish the production and generating
capability of a site.
 The identified project sites are ranked according to size, cost, electric demand, etc.
 Preparation of resources inventories and their updating is a continuous process and should not
be stopped at any time.
 A. Reconnaissance Study

 It is the first stage of the project planning phase and it is preliminary in nature.
Objectives:
 To collect extensive primary and secondary data in order to
 Establish the existing condition, i.e., specify clearly the problems and
opportunities,
 Formulate alternative options to address the problems and opportunities,
 Evaluate effects of the formulated alternative options,
 Make comparisons between the alternative options,
 Make initial recommendation with respect to the technical and economic viability
of the proposed project,
 Select recommended options,
 Plan detailed surveys and investigation required for the recommended options,
Activities:
 The activities involved at this stage are
 Data collection,
 Field visit / reconnaissance survey,
 Desktop investigation.
 In data collection, basic data that are relevant to the project and already available in
various forms are collected.
 Field visit or inspection /Reconnaissance survey, reconnaissance survey is carried
out to establish the existing condition at the planned project sites,
 In desk top investigation, from the gathered data and reconnaissance survey, the
major problems / opportunities that lead to the initiation of the project are properly
identified and articulated,
Major tasks
1. Determine quantitatively electric power demand or opportunity to be exploited:
 How much is the power demand that needs to be addressed
2. Conduct inventory of energy resources:
What are the energy resources available at and near the demand center?
3. Determine the theoretical hydropower potential:
What is the hydropower potential looks like
a) River flow data (Q)
b) Available and created head (H) from Topographic map (potential sites for
hydropower developments)
• Run-of-river
• Diversion canal
• Storage type
c) Determine the theoretical hydropower potential
4. Formulate different alternatives
5. Select two or three alternatives for further study and investigation

Reporting
 A Reconnaissance Study Report covering all the aspects mentioned above will be
prepared.
 B. Prefeasibility Study
 It is the second stage of the project planning phase.
Objectives:
 Its principal objective is to collect additional data and carry out detailed investigations to
 ascertain the technical, economical, financial, social and environmental viability of the
proposed project,
 prepare preliminary engineering design and cost estimate of the options that are
recommended in the reconnaissance stage,
 evaluate potential environmental impact,
 compare the recommended options in terms of technical, socio-economic, financial,
environmental aspects
 arrive at a preferred option from the recommended options,
 plan detailed surveys and investigation required for the preferred option,
Activities
 The activities that are carried out at this stage include but not limited to:
 Collection and evaluation of additional existing data.
 Field surveying
 Field exploration and investigation
 Water resources investigation
 Preliminary design of the recommended options,
 Environmental and social impact assessment

Major Tasks
A. Hydrological &Topographical Survey
B. Electric Power Demand Estimation
C. System design
E. Engineering Cost Estimate
F. Energy Output and Revenue Estimation
G. Environmental and Social Impact Assessment
 i. Hydrological &Topographical Survey.
 Hydrological analysis are carried out to establish Flow duration curve (plot of flow
(Q) versus the percent of time a particular flow can be expected to be exceeded).
Long term flow records
 Rainfall – runoff of models (catchment geology and soil types)
Long - term information might be backed up by short-term flow measurements.
• The daily, weekly, or monthly flow over a period of several years, to
determine the plant capacity and estimate output,
• Low flows, to assess the primary, firm or dependable power.
 ii. Electric Power Demand
 Power demand is defined as the total load, which consumers choose, at any instant
of time, to connect to the supplying power system.
The amount of load used at various hours of the day may vary depending upon the
requirements of the consumption (Daily Load Curve).
 Peak load (determines the size of the plant)
 Average load
 Base load
Peak Load

Average Load
Load
[MW]
Base Load

0 6 12 18 24

Time
 iii. System design

 This would include determination of plant capacity and a description of the overall
project layout, including a drawing showing the general arrangement of the site.

 The prominent aspects of the works should be described in detail, covering:

Civil works
• Design of dams and weirs,
• Design of conveyance structures: intake channel, penstock, tail ace
• Design of power house
The generating equipment
• Selection of number and type of turbine,
• Selection of generator,
• control system
 Grid connection
 iv. Engineering Cost Estimate
A clear system costing would include a detailed estimate of the capital costs of the
project, subdivided into:
Civil costs
The cost of grid-connection
The cost of electro-mechanical equipment
Engineering and project management fees

v. Estimate of energy output and annual revenue.

This would summarise the source data (river flows, hydraulic losses, operating head,
turbine efficiencies and methods of calculation) and calculate the output of the scheme
in terms of
 the maximum potential output power (in kW) and
the average annual energy yield (kWh/year) converted into annual revenue
 vi. Environmental and Social Impact Assessment Impact:
inhabiants
national heritatage
flora and fauna wildlife and fisheries

Reporting
- A Feasibility Study Report covering all the aspects mentioned above will be prepared.
 C. Feasibility (Detail Study)
 It is the last stage of the project planning phase
 Feasibility studies are carried out to determine the technical, economical and
environmental viability of a project. This phase of investigation consists of a
detailed study which is directed towards the ultimate permission, financing,
final design and construction of the project under investigation.
Objectives:
 Its principal objective is to collect additional data and carry out detailed design works
of the preferred option. This include preparation of
 Detailed hydraulic and structural design,
 Construction drawings,
 Technical specifications that clearly detail the required construction methods,
material; types, material classes, and testing requirements,
 Environmental and social impact assessment
 Engineering cost estimate and tender documents.
 Activities:
 The major activities in this stage are:
 Review of the feasibility study,
 Detailed field investigation as per the recommendation of the prefeasibility
study:
 Detail design:
 Preparation of the final contract documents,
 Reporting which includes the above mentioned objectives and activities in
detail.
Reporting
 A Design Study Report covering all the aspects mentioned above will be prepared.
Tender and Contract Documents Preparation
 After the design study report is accepted and approved, the planning phase will
culminate with the preparation of well-organized tender document for competent
bidder selection, and preparation of a standard contract document
 Implementation Phase
 Project implementation is a multidisciplinary job which
include:
 Approval and appropriation of funds
 Pre-qualification and hiring of consultants
 Detailed design
 Preparation of tender/contract documents
 Pre-qualification of contractors
 Preparation of construction design and engineering design
 Preparation of operation manual
 Construction supervision
 Construction of civil works
 Supply and erection of equipment
 Testing, commissioning and commercial operation
 Preparation of completion report
 Hydraulics and Hydrology of Hydropower

Hydraulic Theory
 The principal parameters necessary in making hydropower studies are
Water discharge (Q) and
Hydraulic head (h);

 In hydraulic theory of hydropower, one is essentially dealing with the relationship

between
Electric power (P), and Discharge (Q) and Hydraulic head (h).

Two approaches are available to establish this relationship

 Energy –Work approach
 Bernoulli equation approach
 Energy – Work – Approach

 Consider an elemental volume of water dV

 If the elemental volume of water
dV moves from position 1 slightly below the head
water level to position 2 at the surface of the tail
water, the work done is represented by dW

dW = work done by elemental volume of water, Joule

ρ = density of water, Kg/m3
g = gravitational acceleration, m/s2
dV = elemental volume of water, m3
h = vertical distance moved by the elemental volume of
water, m
To account for the headloss in the penstock, position 1 is taken at a level lower
than the headwater surface level.
 If the elemental volume of water dV moves from position 1 to 2 in some
differential units of time dt, the elemental discharge is then

 Therefore, the power extracted by the hydropower unit is the rate of doing work
and can be represented mathematically as follows

where dP = elemental amount of power, Watt

 Summing the elemental power components of the total discharge passing
through the turbine

The foregoing equations are for theoretical conditions. The actual output is
diminished by the fact that the turbine has losses in transforming the potential and
kinetic energy into mechanical energy. Thus an efficiency term η, usually called
overall efficiency, must be introduced to give the standard power equation
 Bernoulli Energy Equation Approach
The Bernoulli equation is related to the energy grade line, hydraulic grade line, and
the position grade lines.

V = water velocity
P = pressure
Z = potential head referenced to datum
  Considering frictional loses

Gross head: Gross or static head is

determined by subtracting the
water surface elevation at the tailwater of
the powerhouse from the water surface
elevation of the forebay.

Effective head / net head: Net head

represents the actual head available for
power generation. Head losses due to
intake structures, penstocks, and outlet
works are deducted from the gross head to
establish the net head.

The Bernoulli equation for the hydropower installation is written between point 1 at the
surface of the forebay and point 2 at the entrance to the turbine
  When the Bernoulli equation is written between point 2 and point 3 which is the
surface of water at the exit to the draft tube;

 For practical purposes, V1, P1 and P3 are set to zero, solving for P2

 Solving for h;

h is the net head or the effective head

Because the Bernoulli equation defines terms in units of N meter per N of water
flowing through the system, it should be recognized that the N of water flowing through
the turbine per unit of time by definition is

the theoretical power delivered by the water to the turbine as

 Hydrological Analysis
 Earlier it was pointed out that the principal parameters necessary in making
hydropower studies are water discharge (Q) and hydraulic head (h) and
measurement and analyses of these parameters are primarily hydrologic problems;

A: Hydraulic head measurement

Identifying the vertical distance between the water level in the forebay or
headwater of the hydro-plant and in the tailrace is part of a hydrologic problem.
 Determination of the potential head for a proposed hydropower plant is a
surveying problem that identifies elevations of water surfaces as they are
expected to exist during operation of the hydro-plant;
Because the headwater elevation and tailwater elevations of the impoundment
can vary with stream flow, it is frequently necessary to develop headwater and
tailwater curves that show variation with time, river discharge, or operational
features of the hydropower project.
B: Discharge Analysis
The water discharge is a much more difficult problem to cope
 spatial variation: tributary and diversion;
 temporal variation: variation in precipitation, evaporation, and groundwater
recharge that affects the magnitude of stream flow.
 Stream flow data of interest are
 The most common types of streamflow data used for estimating water available
for power production are
mean daily,
mean weekly and
mean monthly flows.
This data is often summarized in flow duration curves.
Low flows, to assess the primary, firm or dependable power.
 Mean Daily Data
can be used directly to develop flow duration curves for estimating the power
potential of small hydro projects.
It is also used to help evaluate projects where little or no seasonal storage is
available for power generation either at-site or upstream.

Mean Weekly and Monthly Data.

Mean weekly and monthly data are obtained from mean daily flow records.
These values are sometimes used in place of daily data in power calculations in
order to reduce computation time.
Precaution:
Where flows vary widely within the week or month, an average weekly or
monthly value may overestimate the amount of streamflow available for
generation.
 Stream flow Analysis – Flow Duration Curve

Stream flow data are usually available as time series data (flow in chronological
order, flow against time):
550
500
450
400
350
300 Series1
250
200
150
100
July

July

July

July

July

July

July

July

July

July
Oct

Oct
Oct

Oct

Oct

Oct

Oct

Oct

Oct

Oct
Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr
Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan
 For evaluating the power out put of a hydropower plant, flow-duration curves are
more suited.
 Flow duration curve is
• is a plot of streamflow versus the percent of time a particular flow can be
expected to be exceeded.
•It summarizes streamflow characteristics and can be constructed from daily,
weekly, or monthly streamflow data.
Unlike time series plot where the flow are ordered chronologically, in flow duration
curves, flow are reordered in terms of their magnitude.
 ordinate: flow
 abssica: percent of the time the given flow is equaled or exceeded
 Two methods are available for the construction of flow duration curves
 rank order method,
 class interval method,
 Rank Order Method
A total time series of flows that represent equal increments of time (daily, weekly,
monthly yearly) is considered
 The flows are ranked according to their magnitude. Individual order numbers are
given to the rank-ordered values. The largest beginning with order 1.
 Exceedance percentage, i.e., the percent of time that the mean flow has been
equalled or exceeded during the period of record,
= Order number X 100
Total Number of Record
The flow value is then plotted versus the respective computed exceedance
percentage.
References to the flow duration values at specific exceedance value are usually made
as Q50, Q30, QI0, and so on, indicating the flow value at the percentage point
subscripted.
Example 1. The following is the record of average yearly flow in a river for 15 years.
Construct the flow duration curve for the river by the rank order method and calculate
Q50, Q30
Year 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970
Flow
(m3/s) 905 865 1050 1105 675 715 850 775 590 625 810 885 1025 1150 925

1400

1200 Streamflow

1000

800
Q

600

400

200

0
1956

1960

1963

1964

1967
1957

1958

1959

1961

1962

1965

1966

1968

1969

1970
Year
1. Reorder the stream flow
interms of magnitude. Order Year Q Order No Q
Excedence
Probability
from the maximum to the 1956
1957
905
865
1
2
1150
1105
6.67
13.33
minimum 1958 1050 3 1050 20.00
1959 1105 4 1025 26.67
1960 675 5 925 33.33
905
2. Assign order number. Starting 1961
1962
715
850
6
7 885
40.00
46.67
with 1 for the maximum. 1963
1964
775
590
8
9
865
850
53.33
60.00
1965 625 10 810 66.67
1966 810 11 775 73.33
3. Calculate the exceedance 1967 885 12 715 80.00
675
percentage (%) 1968
1969
1025
1150
13
14 625
86.67
93.33
1970 925 15 590 100.00

Total No of
Record = 15

e.g, Q = 1150; Order No =1; Total No of record =15; Excedeence Perc = 1/15 *100 = 6.67%

4. Plot Q vs Exceedance
Probability
 Flow Duration Curve
1200

1100

1000

900
Q (m3/s)

800

700

600

500
0 10 20 30 40 50 60 70 80 90 100
Exceedance Probability (%)

Q50 = 870 m3/s; Q30 =970m3/s

 When a multi year monthly stream flow data is available, there are two approaches
for the rank order method.
(i) the total period approach, and
(ii) the calendar year approach.
Total period approach:
 The entire available record is used for drawing the FDC.
e.g. If a ten year monthly average data is availble, The FDC would be drawn
using all the 120 values
Calendar year approach:
 Each year’s average monthly values are first arranged in descending order.
Then the average flow values corresponding to the driest month, second driest
month, and so on up to the wettest month are found out by taking arithmetic mean
of all values of the same rank.
These average values are then used for plotting flow duration curve.
 Such a curve would have only 12 points.
  Class Interval Method
 First, the time series of flow values are categorized into class intervals.
Class upper limit
 The number of flows in each class interval is tallied, Class
Approach A Class lower limit
 For each class, the number of values greater than the upper limit of the class is
determined.
 Exceedance percentage = number of flows greater than the upper limit of a class
interval divided by the total number of flow values in the data series,
 The flow duration curve is produced by plotting the upper limit of the class intervals
against the computed exceedance percentage.
Approach B
For each class, the number of values greater than or equal to the lower limit of a class
is determined.
 Exceedance percentage = the number of flows greater than or equal to the lower limit of
a class interval divided by the total number of flow values
The flow duration curve is produced by plotting the lower limit of the class intervals against
the computed exceedance percentage.
Ex 2. The following data are obtained from the records of the mean monthly flows of
a river for 10 years (1996 – 2005). Calculate the flow duration curve by the class
interval method
Year Month Q (m3/s)
Jan 225 Jan 235 Jan 240 Jan 195 Jan 106
Feb 265 Feb 272 Feb 285 Feb 264 Feb 255
Mar 345 Mar 330 Mar 345 Mar 310 Mar 320
Apr 360 Apr 325 Apr 380 Apr 340 Apr 336
May 370 May 355 May 395 May 375 May 361
June 395 June 365
1996 1998 June 405 June 382 June 376
July 440 2000 2002 2004
July 420 July 445 July 435 July 416
Aug 502 Aug 470 Aug 540 Aug 490 Aug 495
Sep 430 Sep 415 Sep 475 Sep 427 Sep 431
Oct 335 Oct 320 Oct 345 Oct 330 Oct 315
Nov 290 Nov 262 Nov 290 Nov 258 Nov 263
De 245 De 225 De 240 De 233 De 218
Jan 180 Jan 185
Feb 230 Jan 190 Jan 102 Jan 108
Feb 240 Feb 225 Feb 274 Feb 275
Mar 335 Mar 325
Apr 340 Mar 315 Mar 305 Mar 310
Apr 333 Apr 335 Apr 325 Apr 345
May 365 May 360
June 375 May 354 May 384 May 391
1997 June 375 June 372 June 392 June 377
July 430 1999 2001 2003 2005
July 445 July 410 July 422 July 405
Aug 460 Aug 465
Sep 425 Aug 480 Aug 475 Aug 485
Sep 420 Sep 418 Sep 442 Sep 416
Oct 295 Oct 298
Nov 265 Oct 290 Oct 285 Oct 317
Nov 275 Nov 266 Nov 274 Nov 259
De 235 De 215
De 223 De 232 De 217

500
400
300 Series1
200
100
July

July

July

July

July

July

July

July

July

July
Oct

Oct

Oct

Oct
Oct

Oct

Oct

Oct

Oct

Oct
Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr

Apr
Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan

Jan
1. Categorize the time series in to class intervals
 120 flow records, min 120 m3/s; max 540 m3/s
 9 class intervals covering all flows
2. Tally the number of flows in each class interval
3. Approach A:
 For each class, the number of values greater than the upper limit of the class is determined.
 Exceedance percentage = number of flows greater than the upper limit of a class interval divided by
the total number of flow values in the data series,
 The flow duration curve is produced by plotting the upper limit of the class intervals against the
computed exceedance percentage.

Approach A Approach B
Mean monthly No. of No of Exceed Prob No of Exceed
flow range occurrences Occurence > (%) Occurence >= Prob (%)
upper limit lower limit
500-549 2 0 0.00 2 1.67
450-499 9 2 1.67 11 9.17
400-449 20 11 9.17 31 25.83
350-399 21 31 25.83 52 43.33
300-349 24 52 43.33 76 63.33
250-299 21 76 63.33 97 80.83
200-249 16 97 80.83 113 94.17
150-199 4 113 94.17 117 97.50
100-149 3 117 97.50 120 100.00
 600

500

400

300
Q

200

100

0
0 10 20 30 40 50 60 70 80 90 100
Exceedeance Probability
Exercise:

For the10 year monthly streamflow data given above, determine the FDC by the rank
order method using
A - the total period approach, and
B - the calendar year approach.
 Characteristics of Flow Duration Curves

 The flow duration curve (FDC) shows how flow is distributed over a period (usually a
year).
 Catchment characteristics governs shapes of flow duration curves.
1. Generally, a steep flow duration curve implies a flashy catchment – one which
is subject to extreme floods and droughts.
 Flashy catchments are characterized by:
 Rocky, shallow soil,

 Lack of vegetation cover,

 Steep, short streams,
 Uneven rainfall (frequent storms, long dry periods).
 Such type of FDC (i.e. steep) is bad for hydropower development (especially
run-of-river type).
 2. A flat flow duration curve is good because it means that the total annual flow
will be spread more evenly over the year, giving a useful flow for longer
periods, and less severe floods.
 Characteristics of a flat FDC are:
 Deep soil,
 Heavy vegetation (e.g. jungle),
 Long gently sloping streams,
 Bogs, marshes,
 Even rainfall (e.g. temperate climate).
 The time interval that is choosen for the construction of FDC depends on the purpose
of the study.
 As the time interval increases the range of the curve decreases (see Fig.).

 Daily flow rates of small storms are useful for the pondage studies in a run-of-
river power development plant,
 Monthly flow rates for a number of years are useful in power development plants
from a large storage reservoir
 Other Hydrologic Considerations
 Hydrologic information is also needed for
 developing tailwater curves,
 area-capacity curves for reservoirs,
 determination of seasonal losses from reservoirs due to evaporation
 rule curves for operating reservoirs, and
 sedimentation and flood analysis for spillways.
A. Tailwater Relationships
 The tailwater elevation below turbine outlet fluctuate
 due to water released from spillways
 Information on normal tail water, maximum tailwater, and minimum tailwater
elevations is necessary to determine design head and to determine the appropriate
turbine setting.
 Therefore, it is important to develop a tailwater elevation versus river discharge curve
over the complete range of flow that is to be expected.
 Preparing such a curve requires an adequate contour map of the river channel x-area
and an estimation of velocity in the channel at various stages of flow.
 B. Area-Capacity Curves
 Most hydropower developments involve an impoundment behind a dam.

 As the water in storage in the impoundment is released the headwater elevation

changes and this will influence the design of the plant and the pattern of operation.
 Therefore, it is necessary to have a storage volume versus impoundment surface
elevation curve or table.
 At the same time there is need to know water surface area versus impoundment
elevation (evaporation loss calculation).
 This information can be obtained by planimetering a contour map of the reservoir
area and making necessary water volume calculations and water surface area
determinations.
 The two curves are typically combined into what is termed an area-capacity curve.

 Figure below is a typical area-capacity curve for a hydropower development.

 C. Reservoir Rule Curves

 In multipurpose reservoirs, when releases from reservoirs are made, the schedule of
releases is often dictated by considerations other than just meeting the flow demands
for power production.
 The needs for municipal water supply, for flood control, and for downstream irrigation
use dictate certain restraints.
 The restraints are conventionally taken care of by developing reservoir operation rule
curves that can guide operating personnel in making necessary changes in reservoir
water releases.
 Figure below shows example of reservoir operation rule curves.
 To be effective, rule curves often require the use of rather careful and extensive
reservoir operation studies using historical flow data and estimates of demands for
water that are likely to occur in the future.
 Energy and Power Analysis
Power Duration Curve
 We have seen in the previous chapter from hydraulics of hydropower that the
theoretical power

 We have also seen that the actual output is diminished by the turbine losses and an
efficiency term (ɳ), usually called overall efficiency, is be introduced to give the
standard power equation:

 If the river course is divided into a number of stretches, the total power can be
described by

 The actual use of the equation for estimating the potential (P); however, is made
difficult due to the fact that the discharge of any river varies over a wide range.
Moreover, the head may also show some variation.
 We have seen in the previous chapter that the temporal variation of discharge is
captured by Flow Duration Curve
 Similarly the change in head (headwater elevation – tailwater elevation) can be
captured with Headwater and Tailwater Rating Curves (HRC, TRC)

Tailwater Headwater
Elevation Elevation

Q
Q
 Since power is proportional to discharge and head, one can also prepare Power
Duration Curve from FDC and the HRC and TRC.
 Like FDC, the power Duration Curve is the plot of power against the percentage of
time the power is equaled or exceeded.
 Generally, for run-of-river schemes, the head variation is considerably less than the
discharge variation. Thus, head could be taken as a constant.
 For such types of plants, the power duration curve will mirror the flow duration curve.
 This is adequate for elementary rough calculations. If, however, a precise power
duration curve is desired, the head corresponding to any discharge is required to be
known.
 A typical power duration curve is shown below

FDC
Q (m3/s)

0 50 95 100
Percentage of time equaled or exceeded

PDC
Power (MW)

0 50 95 100
Percentage of time equaled or exceeded
 Power (MW) P50 Pm P95 P100

0 50 95 100
Percentage of time equaled or exceeded

 Minimum potential power computed from the minimum flow available for 100 % of the time (365 days
or 8760 hours). This is represented as P100;
 Small potential power computed from the flow available for 95 % of time (flow available for 8322
hours). This is represented as P95;
 Average potential power computed from the flow available for 50% of the time (flow available for 6
months or 4380 hours). This is represented as P50;
 Mean potential power computed from the average of mean yearly flows for a period of 10 to 30 years,
which is equal to the area of the flow-duration curve corresponding to this mean year. This is known as
‘Gross river power potential’ and is represented as Pm.
 It would be more significant to find out the technically available power from the
potential power; According to Mosonyi, the losses subtracted from the P values
present an upper limit of utilization;
 Technically available power: With conveyance efficiency of 70% and overall
efficiency of the plant as 80%, a combined multiplying factor of 0.56 should be used
with the average potential power, P50;
Pa  0.56P50
 Example 3. For the example 1 given in previous example, construct the power
duration curve if the available head is 15 m. Calculate the average potential power
and the technically available power with conveyance efficiency of 70% and overall
efficiency of 80%.
Year 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970
Flow
(m3/s) 905 865 1050 1105 675 715 850 775 590 625 810 885 1025 1150 925
A. Construct the Flow Duration Curve
B. Using the Power equation, calculate the theoretical power from the FDC for constant head = 15 m
P=ρgQh ρ = 1000 kg/m3;
g = 9.81 m/s2
h = 15m
Excedence P =ρgQh;
Year Q Order No Q Probability (MW)
1956 905 1 1150 6.67 169.05
1957 865 2 1105 13.33 162.435
1958 1050 3 1050 20.00 154.35
1959 1105 4 1025 26.67 150.675
1960 675 5 925 33.33 135.975
1961 715 6 905 40.00 133.035
1962 850 7 885 46.67 130.095
1963 775 8 865 53.33 127.155
1964 590 9 850 60.00 124.95
1965 625 10 810 66.67 119.07
1966 810 11 775 73.33 113.925
1967 885 12 715 80.00 105.105
1968 1025 13 675 86.67 99.225
1969 1150 14 625 93.33 91.875
1970 925 15 590 100.00 86.73
 Flow Power
1200 180

170
1100
160
1000 150

140
900
Q (m3/s)

P (MW)
130
800
120

700 110

100
600
90

500 80
0 10 20 30 40 50 60 70 80 90 100
Exceedance Percentage (%)

C. Average power = P50 = 128.6 MW

D. Technically available power = 0.7*0.8*128 = 72.03 MW
Example 4. For the example 3, construct the power duration curve if the headwater
and tailwater rating curves are given in the following graph. Calculate the average
potential power and the technically available power with conveyance efficiency of
70% and overall efficiency of 80%.
2101.00 2090.00
Headwater Elevation
2100.80 2089.00

2100.60 Tailwater Elevation 2088.00

2100.40 2087.00

Tailwater Elevation (m)

Headwater Elev (m)

2100.20 2086.00

2100.00 2085.00

2099.80 2084.00

2099.60 2083.00

2099.40 2082.00

2099.20 2081.00

2099.00 2080.00
500 600 700 800 900 1000 1100 1200
Q(m3/s)
A. Construct the Flow Duration Curve
B. Read from the headwater and tailwater rating curves, the headwater elevation and the tailwater
elevation for each discharge value.
C. Calculate the gross head h;
h = Headwater Elevation – Tailwater Elevation
D. Calculate power P = ρ g Q h
ρ = 1000 kg/m3;
g = 9.81 m/s2
h is variable

Excedence Headwater Tailwater Gross Head P =ρgQh;

Year Q Order No Q Probability Elevation (m) Elevation (m) h (m) (MW)
1956 905 1 1150 6.67 2100.11 2086.09 14.02 158.01212
1957 865 2 1105 13.33 2100.10 2085.92 14.17 153.48302
1958 1050 3 1050 20.00 2100.07 2085.71 14.37 147.83499
1959 1105 4 1025 26.67 2100.06 2085.61 14.46 145.2255
1960 675 5 925 33.33 2100.02 2085.18 14.84 134.51078
1961 715 6 905 40.00 2100.01 2085.09 14.92 132.31249
1962 850 7 885 46.67 2100.00 2085.00 15.00 130.095
1963 775 8 865 53.33 2099.99 2084.91 15.08 127.85794
1964 590 9 850 60.00 2099.98 2084.84 15.15 126.16709
1965 625 10 810 66.67 2099.96 2084.64 15.32 121.60209
1966 810 11 775 73.33 2099.94 2084.47 15.48 117.53883
1967 885 12 715 80.00 2099.91 2084.15 15.76 110.41651
1968 1025 13 675 86.67 2099.88 2083.93 15.96 105.55278
1969 1150 14 625 93.33 2099.85 2083.63 16.22 99.335381
1970 925 15 590 100.00 2099.82 2083.41 16.41 94.887318
 PDC
170
160
150
140
130
P (MW)

120
110
100
90
80
0 10 20 30 40 50 60 70 80 90 100
Exceedance Percentage (%)

C. Average power = P50 = 128.98 MW

D. Technically available power = 0.7*0.8*128.98 = 72.22 MW
 Load Terminologies
Load and Demand

 Power is needed for a variety of purposes such as

domestic,
 commercial,
 industrial,
municipal,
agricultural,
public transport etc.
 The terms load and demand are used synonymously
Load
the amount of power that is actually delivered to or received by consumers
at any instant.
Demand
refers to the amount of power needed or desired by consumer at any instant;
 Load Curve
 The amount of load that is used at various hours of the day may vary depending up
on the requirement of consumption.
 A curve that displays load against time is known as the load curve
 A Daily Load Curve is a curve drawn between load as the ordinate and time in hours as the
abscissa for one day.
Peak load

Note: The area under the

Load (MW)

Average load
load curve represents the
energy consumed in kWh;
Base load

0 2 4 6 8 10 12 14 16 18 20 22 24
Time

1. Base load: the total load that is continuously exceeded;

2. Average load: the area under the curve divided by time.
3. Peak load: the highest instantaneous load. Generally, peak load is defined as
that part of the load carried at intensity greater than 4/3 times the average load
intensity. The peak load determines the size of the hydro plant and its cost.
 3. Peak load: the highest instantaneous load
• Generally, peak load is defined as that part of the load carried at
intensity greater than 4/3 times the average load intensity.
• The peak load determines the size of the hydro plant and its cost.
 Load Factor:
 The ratio of the average load to the peak load is known as load factor.

 A daily load factor may also be defined as the ratio of the actual energy
consumed during 24 hours to the peak demand assumed to continue for 24
hours, i.e.

Load factor gives an idea of degree of utilization of capacity;

Thus, an annual load factor of 0.45 indicates that the machines are producing
only 45% of their yearly production capacity.
Capacity Factor: (plant use factor or plant factor)

For example, if a plant with a capacity of 100MW produces 6,000,000 kWh

operating for 100 hours, its capacity factor will be 0.6, i.e

The capacity factor for hydroelectric plants generally varies between 0.25 and 0.75.
The capacity factor would be identical with load factor if the peak load were equal to
the plant capacity. However, the load factor would be different if the plant were not used
to its full capacity.
Thus, in the above example, if the peak load was 75 MW instead of 100 MW, then
 Utilization Factor: is the ratio of the quantity of water actually utilized for power
production to that available in the river. If the head is assumed to be constant, then
the utilization factor would be equal to the ratio of power utilized to that available.

 The value of utilization factor varies between 0.4 and 0.9 depending on the plant
capacity, load factor and storage.
 From the definition of capacity factor, load factor and utilization factor, it would be
noticed that if the load factor is very high and there is full pondage available at the
plant, the utilization factor may go as high as 1.00 whereas the capacity factor would
go only up to value of about 0.75. The capacity factor could be equal to unity only
with a 100% load factor, complete pondage, complete storage, and at the plant
capacity equal to the average flow. Obviously, such a proposition is only hypothetical
 Load factor approaching zero. The
Peak
load duration curve will approach a
narrow spike, i.e., a peak load of very Load
short duration with very low or no load
during the major portion of the time.
Average

Time

As the load factor approaches

unity, the duration curve will be
somewhat rectangular in
appearance, indicating high
sustained loads.
Load

Time
 Load Duration Curve

 Study of the variation of load and various factors such as load factor, capacity factor
etc for a particular duration (day, week, month) is to use load curves.;
 When the duration is very long, e.g., year, load curves become cumbersome.
 daily load curves are prepared
 The daily load curves are utilized for various calculations on annual basis

 Another convenient and simple way is to utilize Load Duration Curves

 It is a plot of loads and the percentage of time these loads or higher occurred.

 The area under load duration curve for a time duration would be the same as that of a
load curve for the same particular period of time.
 The area under a load duration curve represents the total energy production for the
duration.
 Thus, annual load factor is given by the ratio of the area under the curve to the area
of the rectangle corresponding to the maximum demand occurring during the course
of the year.
  The firm power could be increased by the use of pondage (storage).

Curve without
storage

Curve with
storage

Discharge

Primary power
with storage
Primary power without storage

0 100
Percentage of time

 Secondary power: Also known as surplus or non-firm power, is the power other
than the primary power and is, thus, comparatively less valuable
 Estimation of flow to ungauged sites:

 Methods are required to develop extrapolation of measured flow

duration data which will be representative of a given site on a
stream.
 Several methods to estimate flows from ungauged catchments:
a) Regional frequency analysis,
b) Sequential flow analysis and
c) Use of Parametric Flow Duration Curve.
 A regional analysis usually consists of
the following steps
 Selecting components of interest, such as mean and peak discharge
 Selecting definable basin characteristics of gauged watershed:
drainage area, slope, etc.
 Deriving prediction equations with single or multiple linear
regression analysis
 Mapping and explaining the residuals (differences between computed
and observed values) that constitute “unexplained variances” in the
statistical analysis on a regional basis.
 Cont.….
 Some of the project sites are situated either upstream or downstream
of the stream gages.

 In this case the stream flow data of the sites will have a considerable
difference from the recorded data.

 There are also some project sites which have stream flow data neither
upstream nor downstream
 Cont.….
Hence based on the above conditions the selection of source and data
analysis performed has been summarized as follows
A) Direct data from the gauged stations:
Depending on the similarity of area between the proposed reservoir site
and the stream flow gage location, direct mean monthly stream flow
data was computed from the available years mean monthly data of the
gauged stations updated to the recent record.
B)Simple Area ratio method
 The area ratio method was used to determine the flows
at the required sites from the main or tributary rivers
mean stream gauge values.

 Flow values are transferred from a gauged site, either

upstream or downstream to the ungauged site
Rumenik (1996).

 The area ratio method formula and the pre conditions in

utilizing the formula have been set as follows.
 Cont.….

Asite n
Qsite ( ) * Qgauge
Agauge
 Where
 Qsite is the discharge required at the reservoir site
 Qgauge is the discharge at the near by gauge site
 Asite and Agauge are the drainage areas at the reservoir and gauge
respectively.
 n is a coefficient that varies between 0.6 and1.2
 If Asite is 20% of the Agauge or lies with in the range of
0.8<=Asite/Agauge<=1.2 then n=1
 Cont.….

 The steps followed during applying the simple area ratio

method was given by Rumenik (1996) as follows.
1) Locate the nearest gauge sites.
2) Determine the drainage area for the ungauged site
between the gauged sites.
3) Multiply the mean flow at the gauged site by the
drainage area of the ungauged site and divide by the
drainage area of the gauged sites.
 The area ratio method was employed for those areas
where Asite is 20% of the Agauge or the ratio Asite/Agauge
lies with in the range of 0.8-1.2
 Cont.….

c)Weighted Area ratio method: -

 This method was employed for the computation of mean flow of a
given dam site situated in between two flow gages.
 It considers the weighted area ratio of upstream and down stream
gages catchment area. When Asite is with in 50% of the Agauge.
 The governing formula employed for thecomputation is given as:
 Cont.….

( Aguage1  Asite ) * Qgauge1  ( Asite  Agauge2 ) * Qgauge2

Qsite 
Aguage1  Agauge2
 Where the suffixes 1 and 2 represent downstream
and upstream discharge and areas respectively.
 This technique was mainly applied for those sites
where there is upstream and downstream flow gages
and having Asite/Agauge ratio beyond the limit given
for the simple area ratio method.
 Cont.….

 Inthe figure (next slide) Qc is the discharge capacity of the plant

under the design head.

 This Qc is the discharge at full gate opening of the runner under

design head.

 Stream discharge to the left of Qc on the flow duration curve is

greater & must be bypassed by a spillway.

 To the right of the runner discharge capacity point, Qc, the amount
flowing in the river go through the turbine . This shows that full-
rated power production will not be produced.
 Residual, reserved or compensation flow :

Measurement of gross head

Estimation of net head

 Residual, reserved or compensation flow

Estimation of plant capacity and energy output

 The FDC provides a means of selecting the right design discharge

 Taking into account the reserved flow and the minimum

technical turbine flow, the plant capacity and the average annual
energy output can be estimated.

 Design flow is assumed to be, in a first approach, the difference

between the mean annual flow and the reserved flow
 Cont.….
 Design flow(Qm-Qres), + net head  suitable turbine types

 The gross average annual energy (kWh), E = fn (Qmedian, Hn,

ηturbine, ηgenerator, η gearbox, ηtransformer, γ,h)

 The capacity of each turbine (kW)=design flow (m3/s)*net

head (m)*turbine efficiency (%)*specific weight of the water
(kN/m3)
SOLVED EXAMPLE

 The average monthly flows of a stream in a dry year are as

follows:
Cont.….
 Cont.….

Pfirm = gHQ = 0.9*9810*20*45 = 7.95MW

Psecondary = area under power duration curve

b/n 150 & 45 m3/s = 10MW
Cont.….
Hydropower Engineering II

Chapter Two
POWER PLANT STATIONS
 Components of Hydropower Projects
 To generate electric power from water, three basic elements are necessary
1. A means of creating head: Dams, Weirs, barrages etc
2. A means for conveying water from dam to turbine
 Intake: directs water from reservoir to penstock/power conduit
 Power canal,
 Forebay,
 Penstock: pressurized conduit conveying water to turbines
 Draft tube:
 Surgetank:
 Tail race:
3. A power plant: power house to generate electric power
• Turbines: converts potential and kinetic energy of the water to mechanical
energy
• Generators: converts mechanical energy to electrical energy
 Storage type Hydroelectric Power Plant

2
Draft Tube
 Dams, Barrages and Reservoirs
 Water control structures: dams, barrages, and weirs play two major functions.
 It creates the head necessary to move the turbine, and
 It stores water used to maintain the daily or seasonal flow release pattern.
 The height of the dam or diversion weir establishes the head and storage from
available water for generation.
 Storage capacity is the volume of a reservoir available to store water.
 This storage is divided into active and inactive storage.
o Active storage: that portion of the storage capacity in which water will
normally be stored or withdrawn for beneficial uses.
o Inactive storage: that portion of the storage capacity from which water is not
normally withdrawn, in accordance with operating agreements or restrictions.
 1. Active storage

2. Inactive storage

3 Live storage

4 Dead storage

5 Flood storage

6.Reservoir capacity; gross capacity of reservoir; gross storage; storage capacity

7.Retention water level; top water level; full supply level; normal water level
8.Flood surcharge; surcharge
9.Maximum water level; top of joint use (joint use means that part of the reservoir
capacity including both surcharge & empty part of the active storage, assigned to
flood control or conservation depending on the time of the year)
10.Minimum operating level; top of inactive storage
11.Freeboard
 Intakes
 A structure that is constructed to divert the required amount of water from a
source such as reservoir or river into a power canal or into a penstock that convey
the water to a power house without producing a negative impact on the local
environment and with the minimum possible head loss.
 Intakes are usually provided at the entrance of a power canal or penstock

 It can be provided as
 an integral part of the dam / weir or
 in isolation from the diversion weir or dam
Intake as integral part of the Dam

Gate

Bellmouth
Trashrack

Draft Tube
 Functions of Intakes
 The main functions of intakes are:
1. To control flow of water into the conveyance system.
 The control is achieved by a gate or a valve.
2. To provide smooth, easy and vortex or turbulence free entry of water in
the conveyance system to minimize head loss.
 This can be achieved through providing bell-mouth shaped entrance.
3. To prevent entry of coarse river born trash matter such as boulders, logs,
tree branches etc.
 Provisions of trash racks at the entrance achieve this function.
4. To exclude heavy sediment load of the river from interring the conveyance
system.
 Special devices such as silt traps and silt excluders are used to control & trap
the silt.
 Power Canals
 It is an appropriate choice when the general topography of the terrain is moderate
with gentle slopes.
 However, when the topography is highly rugged and with steep slope
 It becomes uneconomical to construct canals on the grounds that
 as the canal follows longer distances; and
 may need provision of cross-drainage works and deep cuts and fills at a
number of appropriate locations.
 In such cases, it is advisable to go for tunnels or pipes.
 The choice, in fact, has to be made based on economic analysis.
 Where the topography of the region presents special formations, the alternating
use of open-canal and open-surface tunnel sections may ensure the most
economical development.
 Tunnels
 Tunnels are underground conveyance structures constructed by special tunneling
methods without disturbing the natural surface of the ground. In many modern
high head plants, tunnels form an important engineering feature.
 Advantages of tunnels
 It provides a direct and short route for the water passage thus resulting in
considerable saving in cost
 Tunneling work can be started simultaneously at many points thus leading to
quicker completion,
 Natural land scape is not disturbed
 Tunneling work has become easier with development techniques of drilling and
blasting
 Development of rock mechanics and experimental stress analysis has given
greater confidence to engineers regarding stability of tunnels.
 Forebay
 Acts as a transition section between power canal and penstock.
 Distributes water carried by the power canal among penstocks that lead to
turbines,
 Acts as a regulating reservoir
 Water is temporarily stored in a Forebay in the event of load rejection by the
turbine and is withdrawn from it when the load is instantenously increased..
 Serve as a final settling basin where any water borne debris which either passed
through the intake or was swept into the power canal can be removed before the
water passes into the turbine.
 A forebay is formed simply by widening the power canal at the end.
 Forebay advantages:
 To decrease the length of the penstock,
 To decrease the distance to the power house so as to get the turbine on and off
within a shorter period.
 To halt the propagation of pressure waves to the power canal
Penstocks
 Pipes of large diameter used for conveying water from the source
(reservoir or forebay) to the power house.
 They are usually high-pressure pipelines designed to withstand stresses
 Static pressure and
 Water hammer pressures created by sudden changes in power demands
(i.e. valve closures and openings according to power rejection and demand).
 The provision of such a high-pressure line is very uneconomical if it is too
long, in which case it can be divided into two parts,
 a long low-pressure conveyance (tunnel) followed by short high-
pressure pipeline (penstock) close to the turbine unit, separated by a
surge chamber which absorbs the water hammer pressure rises and
converts them into mass oscillations.
 Surge Tanks
 Surge tanks are vertical standpipes that act as a Forebay and shorten the
distance for relief from the pressure wave of water hammer.

 A surge tank serves for three purpose:

 Flow stabilization to the turbine,
 Water hammer relief or pressure regulation, and
 Improvement of speed control.
 Surge tanks are usually not economical unless most of the drop in elevation in the
penstock occurs near the turbine.
 Power House
A structural complex that shelters the essential equipments needed in hydro-electric
power generation. The major equipments in a power house include:
 Turbines, Generators, Transformers, switch boards; shaft, ventilation, cranes, etc
 Its location and size is determined by site conditions and project layout.
 It could be located within the dam structure adjacent to it or some distance away from the
dam.
 The power house would be located to economically maximize available head while
observing site physical and environmental constraints.
 Power House Types
 There are four types of power house configurations (structure):
 Indoor: encloses all of the power house components under one roof
 Semi-out door: has a fully enclosed generator room.
 The main hoisting and transfer equipment is located on the roof of
the plant
 Outdoor: a generator room is not provided
 Generators are enclosed in a weather proof individual enclosures and
are recessed in to the floor.
 Underground: is often used in mountainous areas where there is limited
space available to locate a power plant.
 It is also used to minimize penstock length in these areas since the
penstock can be located directly below the reservoir.
 Pumped storage powerhouses are often located underground in order
to shorten the penstock and obtain deep settings on the turbines.
 The selection of powerhouse configuration and structure should be based on
Fixed Operation and Maintenance costs
 Power House Planning
 The basic requirement of a power house is the functional utility and the
aesthetic requirements.
 Planning the power house should be harmonious with the surrounding.
 A power house of a hydropower may be classified
Surface power house
 It is founded on earth’s surface and its superstructure rests on the foundation.
 Has no space limitation
 Need an architectural planning to fit with the general landscape.
 Economical choice for low head power plant and small scale developments
Under ground power house
 It is built underground i.e A cavity is excavated inside earth surface where sound
rock is available
 Space limitation.
 Economical choice if a particular area is affected by landslides and if the underlying
geology is suitable,
Surface power house
Surface power house has three sections (excluding the intake):
 Substructure
 Intermediate structure
 Super-structure

Supper structure

Intermediate

Substructure
 Substructure
 It is that part which extends from the bottom of the turbine to the soil or rock. It usually
lies below ground.
 It houses the passage (draft tube / exit channel) for the water coming out of the turbine.
 Hydraulic function: water passageway
 For reaction turbines: it provides a diverging passage (draft tube) where the
velocity of the exit water is gradually reduced in order to reduce the loss in
pushing out the water.
 For impulse turbine: a draft tube is not required and only an exit channel would
serve the purpose.

Exit Channel

 Structural function is dual:

 Safely carry the superimposed loads of machines and other structures.
 Safely transmits the load of the structure above it to the foundation strata
 Intermediate Structure
 It is part of the power house which extends from the top of the draft tube to top of
the generator foundation. It houses the turbine including the spiral case, galleries
for auxiliary machines.

 It contains two important

elements of the power house:
 The spiral case / scroll
case which feeds water to the
turbine.

 Foundation for the

generator. The generator
foundation rests on the scroll-
case which is embedded in the
concrete.
 Hydraulic Function: water passageway
 For reaction turbines: Scroll or spiral is a part of the turbine. It distributes
water coming from penstock uniformly and smoothly through guide vanes to
the turbine.
 For impulse turbine: a manifold supplying water to the nozzles will serve this
purpose.
 Structural Function
The intermediate structure provides structural support to the
generator. Arrangements may be made either to transmit the load
directly to the substructure through steel barrel or through a column
beam or slab.
The structural function of the concrete around scroll case would
depend upon the type of scroll case used:
 If the scroll case is made of steel and strong enough to withstand
internal loads including the water hammer effects, the surrounding
concrete acts more or less as a space fill and a medium to distribute
the generator loads to the substructure.
 If it is a concrete scroll case then this concrete should be strong
enough to withstand the internal hydrostatic and water hammer head
as well as the external superimposed loads on account of the machine
etc.
 Usually, a steel scroll case is used as water liner.
 Superstructure
 It is the part of the power house above the generator floor right up to the roof.
 This part provides walls and roofs to power station and also provides an overhead
travelling crane for handling heavy machine parts.
 Water Passage in Turbines
 Based on the way the hydraulic energy of the water is converted in to mechanical
energy, one distinguishes two types of turbines:
 Impulse turbines;
 Reaction turbines

Impulse turbine
 Impulse turbines
 Utilizes the kinetic energy of the water.
 All the available hydraulic energy is converted in to kinetic energy
 The runner is not filled with water and the pressure distribution along the turbine
runner is almost atmospheric
 The most common example of an impulse turbine is
 Pelton turbine (patented by Pelton in 1889)
 Pelton Turbine (Impulse Turbine)

Shaft (rotating)
connected to
generator

Hydraulic energy of the water is

converted to kinetic energy
A typical impulse turbine has water passageways that incorporate
a. Nozzle : to issue jet of water to strike the buckets attached to the disc of the
runner
b. Manifold: to distribute water from the penstock to each nozzle, if the turbine
has more than one nozzle
c. Runner: jet of water issued from the nozzle (s) strikes the bucket attached to
the disc of the runner which lead to the rotation of the runner
d. Exit Channel / Tail race:

Runner

Exit channel / Tail race

 Runner

115
Bucket
Disc
Turbine
Runner
Shaft
 Reaction turbines
 Utilize both kinetic energy and pressure energy of the water. The
hydraulic energy is converted to both kinetic and pressure energy.
 The runner passage is completely filled with water and the water acting on
the runner blades / vanes is under pressure greater than atmospheric
 The most common example of reaction turbines are
 Francis Turbine (patented by Francis in 1849)
 Propeller and Kaplan Turbines ( patented by Kaplan in 1913)
 A typical reaction turbine has water passageways that incorporate
a. Spiral case / scroll case - to distribute water from the penstock to the
runner
b. Runner: water from the spiral case flows under pressure through the
blades attached to the runner thus changing the pressure and kinetic
energy of the water to mechanical energy
c. Draft tube: conduit to pass the water past the runner back to the tail
water / tail race
 shroud

Vanes

Francis Turbine
Runner
shroud
 Underground Powerhouse
 In deep gorges, areas frequented by quakes, hazardous land and rock slides
underground powerhouses are good alternatives,
 Advantages of underground powerhouse:
 Shorter underground conduit
 Cheaper penstock design (smaller diameter)
 Favorable construction conditions
 Preserve the landscape
 Disadvantages
 Higher construction cost
 Higher operational cost
 The lighting cost.
 The running cost of air-conditioned plant.
 The removal of water seeping
 Turbine Setting
 There are two types of turbine setting: vertical and horizontal

Generator

Generator

Turbine
Turbine

Horizontal
Vertical

 Factors affecting the choice between horizontal and vertical setting of machines are
 Relative cost of plant,
 Foundations,
 Building space and layout of the plant in general.
 Horizontal
Setting

Generator

Francis
turbine
 Horizontal Setting
Shaft

Generator
 Generator

Vertical
Setting

Pelton turbine

123
124
 Vertical Setting
 Vertical arrangements offer many advantages over horizontal especially when
there are great variations in tail-race level.
 Horizontal machines turbine-house should be above the tail-race level or
the lower part of the house must be made watertight.
 The efficiency of the vertical arrangement is 1 to 2% higher than for a similar
horizontal arrangement. This is due to the absence of a suction bend near the
runner.
 In vertical turbine setting as the generator being mounted above the turbine, it is
completely free from flooding.
 Advantages of vertical arrangement:
 More compact and needs less floor area for the power house
 Design of hydraulic passages is simple
 In reaction turbines the runners can be placed nearer to the tail water without
disturbing the PH arrangement.
 Horizontal Setting
 In horizontal machine setting:
 Two turbines could drive one generator, and turbines would operate at
a higher speed bringing about a smaller and lighter generator.
 Though the horizontal machines would occupy a greater length than the
vertical, the foundations need not be so deep as required for vertical
machines.
 The horizontal arrangement require higher settings to reduce or
eliminate the cost of sealing the generator, the auxiliary electrical
equipment and cable ducts against water.
 In actual cases, the overall cost will determine which arrangement to
choose.
 The majority of impulse turbines are of the horizontal shaft types. Mainly
because this setting lends itself readily to the use of multiple runner units.
 The horizontal arrangement is simpler than vertical from constructional and
maintenance point of view.
 Cont.….
 The following items of equipment are considered for planning and
dimensioning of the power house:
 Hydraulic equipment:
 Turbines
 Gate and gate valves
 Relief valves of penstocks
 Governors
 Flow measuring equipment
 Electrical equipment:
 Generator
 Excitors
 Transformers, pumps, cooling systems, connections, funs and plate forms
 Switching equipment:
 Low tension buses
 Switch board panels
 Switch board equipment and instruments
 Oil switching and
 Reactors
 Cont...
High tension system:
 Buses
 Oil circuit breakers
 Lightening arrestors
 Out going connections
Auxiliaries:
 Storage batteries
 Station lighting
Miscellaneous equipment:
 Crane
 Work shops
 Office rooms
 Other facilities,( clinic, Store , etc)
 Power House Dimensions
 The dimensions in the plant are determined by the dimensions of the
 Generating units or
 Dimensions of the spiral case particularly when the head is low.

 The width of the working bay is generally equal to about one unit bay, if the
unit is planned to be major overhauled in the power house.

 If the unit is planned to be major overhauled outside the power house

there can be no working bay in the power house.

 The width of the unit bay is so determined that:
 The clearance between the two units or between the unit and the wall, should
be sufficient for the erection and disassembly of the unit, generally, about 2m.
 Cont...
 The passageway, for the operators should be 1-1.5 m,

 Clearance between the switch board / control panel and other apparatus
should be at least 2m,
 Clearance B/n switchboard and the wall should be about 0.8m.

 For the side unit, its unit bay should have an additional width (about 1m
per Units).
 The determination of the setting elevation of the turbine is very important
for the Power House design, taking in to consideration the minimum
tailrace level and the suction head of the turbine.
 The height of the Power House is mainly determined by over head craning
of the heaviest part of the unit.
 Preliminary dimensions of power House for Medium and large
Hydro (Reaction Turbine installation )
Unit spacing in terms of discharge (for steel scroll case )
Unit spacing in terms of discharge diameter
Cont...
Cont...
 Bay’s Dimension
 The three essential bays in a power house complex are:-
 Unit bay or machine hall
 Erection bay
 Control room
 Machine hall
 Length:
 Depends on the number of units and the size of machine.
 For vertical alignment machine the centre to centre distance is controlled by
the size of the scroll casing layout.
 Standard layout indicates a distance of 4.50 to 5.0D,
where D is the turbine out let diameter.
 Added to this dimension is the minimum clearance of 2 to 3m.
 So, the preliminary dimension between centre to centre of two units is 5.0D
+ 2.5m.
 For higher specific speed it can be 4.0D + 2.5m or smaller.
 Knowing the number of machines, the total length of the machine hall can be
worked out.
 Cont.…
Width:
Width of the machine hall is determined by the size and
clearance spacing between the walls – needed as gangway.
Since the gangway requirement is of the order of 2.5m, as a first
approximation the width of the power house can be presumed to
be at least equal to the centre to center distance of two
machines.
In the Machine hall, the generator placing is not exactly at the
centre of the machine hall but towards one side so as to provide
enough operation space for the crane operator.
Height:
Height of the Machine hall is fixed by the head room requirement
(about 2 to 2.5m) of the crane operation.
The hall must have a height which will enable the crane to lift
the rotor of the generator or the runner of the turbine clear of the
floor without any obstruction.
 Cont....
 Loading and Erection bay:
 This space is required for unloading or loading heavy machines and for its
erection.
 Small assembly is also done on the space.
 The size of the erection should be sufficient to keep the larger parts like
the rotor of the generating unit.
 Service crane:
 The crane should be designed for such a capacity that it can lift the heaviest
component in the power house.
 Normally, the heaviest part is the rotor and the stator.
 Cable and bus bar:
 These are placed in the cable ducts made in the floor of the generator in the bus bar
galleries (cable galleries).
 High voltage cables should be carried separately.
 Switch Yard:
 This is the yard with step up transformers. This should be located near the power
house. In most cases switch yards are kept out side the power house
 Cont.….
Control bay:
The control bay houses the control equipment.

It can be adjacent to the unit bay as in most power houses.

Signal is sent from the control bay to the operating bay from where the

operation control is achieved.

Most of the controls are operated by remote control from the control bay.
Hydropower Engineering II

Chapter Four
TRANSMISSION OF ELECTRIC POWER
 Introduction
Like any other industry, the electric power system may be thought of as
consisting of three main divisions:
 Manufacture, production or generation, cogeneration,
 Delivery or transmission and distribution,
 Consumption.
 Electric Transmission
 Electric power transmission is the bulk transfer of energy, from
generating power plants to electric substations located near demand
centers.
 Transmission lines, when interconnected with each other become
transmission networks.
 The combined transmission and distribution network is known as the
“Power Grid”.
 Cont….
 If the power plant and the load centers are close to each other, the
costs of electric power transmission and maintenance are
minimum.
 But, in most cases power plants are located in remote areas and
inside gorges which demands high cost for transmission of electric
power to load centers.
 A design criterion of transmission lines considers:
The maximum allowable voltage variation from no load to full load
The maximum economic power loss
Protection from lightning and other damages
Structural stability in high winds, in temperate areas, in ice and snow
Safety for people living and working near the lines
Safety of animals and plants which may be affected due to power line
 Classification of Power Line
 Overhead Power Line
 is a structure used in electric power transmission and distribution to
transmit electrical energy along large distances and insulation is provided
by air.
 It consists of one or more conductors (commonly multiples of three)
suspended by towers or utility poles.
 Cont…
Advantage
Using air as the cable insulator, the cable is less expensive
Insulation can be cheap and simple.
Most time used in developing countries.
Disadvantage
Uninsulated cables are exposed to lightning and to falling trees.
The land close to the lines has to be cleared of trees, and this
has to be carried out periodically.
The poles may also have a finite life, and so may need replacing,
perhaps every 15 years.
Less efficient for a given conductor size because the wide
spacing of the conductors gives rise to inductive losses.
 Cont….
Overhead power transmission lines are classified in the electrical
power industry by the range of voltages:
 Low voltage (LV) – less than 1000 volts, used for connection between a
residential or small commercial customer and the utility.
 Medium voltage (MV; distribution) – between 1000 volts (1 kV) and to
about 33 kV, used for distribution in urban and rural areas.
 High voltage (HV; subtransmission less than 100 kV; subtransmission or
transmission at voltage such as 115 kV and 138 kV), used for sub-
transmission and transmission of bulk quantities of electric power and
connection to very large consumers.
 Extra high voltage (EHV; transmission) – over 230 kV, up to about 800 kV,
used for long distance, very high power transmission.
 Ultra high voltage (UHV) – higher than 800 kV.
 Cont…..
 Undergrounding
 Refers to the replacement of overhead cables providing electrical
power or telecommunications, with underground cables.
 Underground lines have to be insulated, and protected against
ground movement, ploughing, new buildings
 Cont….
 Advantage
 Underground cables take up less right-of-way than overhead lines, have
lower visibility, and are less affected by bad weather.
 Once installed, the line should run without maintenance until the
insulating material deteriorates.

 Disadvantage
 Long underground AC cables have significant capacitance, which may
reduce their ability to provide useful power to loads beyond 50 miles.
 Long underground DC cables have no such issue and can run for
thousands of miles.
 Costs of insulated cable and excavation are much higher than overhead
construction.
 Faults in buried transmission lines take longer to locate and repair.
 Planning and Design
 New transmission and distribution systems are planned and designed by
a variety of professionals.
 Transmission planning engineers use information collected by utility
forecasters to identify when and where more power lines are needed
for the system to operate reliably.
 Siting, land rights, and permitting agents work with government
agencies and landowners to acquire land and the rights to use land.
 CAD designers design the layouts for new transmission and distribution
lines and facilities.
 Cont…..
The planning process may have the following phases
Establishing the database
Electrical system data
Load data
Determine the main principles for system layout/renovation
strategy
Technical analysis of different system alternatives
Establishing investment costs and operation costs
Cost minimization
Decision of investment plan
 Design Philosophy of Overhead Lines
The main parts of a power line are
Conductors,
Supports (towers or poles) which hold the bare conductors,
Insulators needed between the conductors and the support
Shield wires attached to tower extensions.
Conductors, supports and insulators constitute the
main types of components of an overhead power line.
Towers keep the conductors at suitable distance from
the ground and other objects (external clearances) and
mutually apart (internal clearances)
 Cont….
Supports need either foundations, or the lower part is buried in
the ground, to keep them in a fixed position, and hardware and
clamps are used to fix the insulators between supports and
conductors
 The clearance has to be large enough to avoid discharge.
 The components must have the mechanical strength to resist the
stresses they are exposed to.
 Standards and regulations are required to layout and design over head
power lines, which outline the criteria for
Electro technical and
Mechanical aspects
 Framework of Standard
 Probabilistic methods
 Based on statistical Knowledge of an event(climate load)
 Loads (Analyzing loads)
 Mechanical aspects: Analyzing the loads acting on the line
 Additional loads:
 Climate loads
 Special loads
 Security loads
 Safety loads
 Electro technical aspects : electrical stresses acting on the line have to be
analyzed
 The loads are classified as the following voltages:
 Continuous power frequency voltage
 Temporary over voltages
 Slow front over voltages
 Fast front over voltages
 Right Way of Planning
Laying to Transmission lines needs extensive work of planning:
The planning process may include:
 Early clarification of possibilities and alternatives
 Close contact with local interests and users of the areas in question
 Recording of all important interests connected with the actual
alternatives
 Consultations where all justifiable feasible alternatives are included

In the process of planning it is very important that the planners

do not choose their own favorite alternative before all relevant
information is brought forward.
 Cont….
 Adaptation to use of land
As a main rule, avoiding the most valuable and conflict filled areas,
where satisfactory alternatives are available should be the aim
 Aim at avoiding
 Evaluate Border zones
 Landscape
The main rule should be that wherever possible and where solutions
are otherwise acceptable, the aim should be to find right of ways
adapted to, and subordinated to the landscape.
 Health Impacts of electric and magnetic fields
In recent years grater attention has been focused on electric and
magnetic fields, both among the general public and experts, as a result
of the fear that these field can constitute a health risk
 Cont….
 Electric and magnetic fields in relation to power lines are important in
this combination even if such fields usually are weak compared to
what is found in other electric sources.
 However, power lines extend over larger areas and thus the public is
regularly, and in some cases permanently, exposed to the fields.
 Cont….
 The electric field ( E-field) The magnetic field ( B – filed)
The electric filed is designated The magnetic induction is
with the latter E and is a measure designated with the letter B and
of the rate of change of the gives the strength of the magnetic
voltage when moving in a certain field in the unit Tesla (T).
direction. It is measured in volts
per meter (V/m).
 Cont….
 Risk of Bird Habitat:
 Power lines affect bird life.
 The power lines may have an impact indirectly on bird life by
disturbing the birds’ habitat
 The risk of bird collision can be reduced by:
 Choosing right of way out side the best isotopes
 Keeping away from natural migration routes
 Leading over head lines of the same dimension conductors heights in
parallel
 Adapting the choice of right of way so that the conductors are
shielded by vegetation or terrain to avoid conductors just above tree
tops.
 Tower Spotting
 Tower spotting is done with the help of land surveying.
 During pegging of the route centre line all necessary information including
measurement of
 crossing lines,
 communication lines,
 houses,
 buildings,
 roads,
 rivers and
 objects along the route and property boundaries have to be recorded.
 Side terrain is measured to both sides of the centre line where the side
terrain is at a higher elevation than the centre line
 The width of the route to be measured is largely dependent on the span
lengths used, snce conductors in longer span have large sags and will thus
swing much more than those with shorter spans.
 Conditions influencing the Tower spotting
 Tower Spotting is used for determining the location and height of
towers on the route profile.
 Several factors can be listed.
Conductor type
Tower type
Terrain type
Climatic loads
Crossings
Clearances to adjacent objects
Building conditions, etc.
 Sag calculations
 Catenary adoption is to draw the catenaries onto the route profile to
check the distance to the ground;
 It is draw for the highest temperature according to relevant regulations
or standard.
Cont…
Cont….
 Cont..

164 CENG 6803

Cont…
Cont…
Cont….
Cont….
 Example
 Calculate the sag for a span of 200m if the ultimate tensile strength of
the conductor is 6000Kg. Allow a factor of safety of 2. The weight of
the conductor is 900Kg/Km.
 Solution
Solution
 Design of Foundations
 The foundations of the towers may be a separate construction upon
which the tower is placed in the case of a conventional wood pole the
poles themselves are dug down in to the ground.
 With regard to foundations as separate parts of the tower they are
usually built on steel reinforced concrete.
 This type of foundation may be divided in to:
Foundation designed to resist compression only
Foundation designed to resist uplift
Foundation designed to resist both compression and uplift
Foundation designed to resist toppling overturning moment
 Construction and Maintenance
 Crews of line workers and utility workers build and fix transmission
and distribution lines.
 Substation mechanics build and maintain the substations that step
power down from power lines to be distributed for residential and
commercial use.
 Millwrights help install and secure large equipment.
 Machinists fabricate special tools that are needed to construct and
operate facilities.
 Operation and Control
 The transmission of electricity across the grid from generation plants to
distribution facilities is done in control rooms by system control
operators.
 Reliability coordinators ensure that enough energy is available from
generating facilities and elsewhere in the grid to meet demand.
 They also respond to and help resolve emergency conditions.
 When power outages occur, outage coordination dispatchers coordinate
the response and send workers out to fix the problems.
 Safety and Regulations
 Electricity is an essential component to modern life, but is also very
dangerous.
 There are many regulations that govern the safety and reliability of
power.
 Safety and occupational health coordinators coordinate safety programs.
 Training and development specialists lead classes that teach employees
how to do their jobs safely and responsibly.
 Electric Power Distribution
 The demand for energy increases over time as populations grow and
create a need for more homes, factories, office buildings, consumer
products, and public infrastructure.
 An Electric Power Distribution system is the final stage in the
delivery of electric power.
 It carries electricity from transmission system to individual
consumers.
 Power Grid

 Transmission network
 To transport the electric power from the point
of generation to the load centers
 All above a certain voltage
 (Sub transmission)
 Distribution network
 To distribute the electric power among the
consumers
 Below a certain voltage
 Distribution System
 Mainly distribution systems are two types
 Primary Distribution (33KV/11KV)
 Secondary Distribution (11KV/440V)
 Household electricity is alternating current (AC)
 Household voltages are typically 120V or 240V
 Three broad classifications of choices need to be considered in
design of distribution system:
 The type of electric system: dc or ac, and if ac, single-phase or poly phase.
 The type of delivery system: radial, loop, or network.
 Radial systems include duplicate and throw over systems.
 The type of construction: overhead or underground.
 Types of Delivery Systems:
 Primary Distribution
 Which carries the load at higher than utilization voltages from the
substation (or other source)to the point where the voltage is stepped
down to the value at which the energy is utilized by the consumer.
 Primary distribution systems include three basic types:
 Radial systems, including duplicate and throwover systems
 Loop systems, including both open and closed loops
 Primary network systems
 Cont…
 Secondary Distribution
 Which includes that part of the system operating at utilization voltages,
up to the meter at the consumer’s premises.
 The maximum generation voltage in advanced countries is 33 kV while
that in India is 11 kV.
 The amount of power that has to be transmitted through transmission
lines is very large and if this power is transmitted at 11kV the line
current and power loss will be large.
 There fore the voltage is stepped to a higher level by using step-up
transformers located in sub-stations.
 Cont….
Distribution system is consist of
Substation Cut out
Utility or Distribution Pole Transformer
Primary wires Neutral wire
Cross arm Secondary wire
Insulators Grounding
Lighting Arrestor Guy wire
 Substation
 A substation is a part of an electrical generation, transmission,
and distribution system.
 Substations may be owned and operated by an electrical utility, or may
be owned by a large industrial or commercial customer.
 Utility pole
A utility pole is a column or post used to support overhead
power lines and various other public utilities, such as cable, fiber
optic cable, and related equipment such as transformers and street
lights.
Most utility poles are made of long straight trees and pressure-
treated with some type of preservative for protection against rot,
fungi and insects.
 Cross arm
 The woods most commonly used for cross arms are Douglas Fir or
Longleaf Southern Pine because of their straight grain and durability.
 The top surface of the arm is rounded so that rain or melting snow and
ice will run off easily.
 The usual cross-sectional dimensions for distribution cross arms are 3.5
inches by 4.5 inches; their length depending on the number and spacing
of the pins.
 Insulator
 An electrical insulator is a material whose internal electric
charges do not flow freely, and therefore make it very hard to conduct
an electric current under the influence of an electric field.
 A perfect insulator does not exist, but some materials such
as glass, paper andTeflon, which have high resistivity, are very good
electrical insulators.
Types of Insulators
 Pin type insulator
 Suspension insulator
 Strain insulator
 Shackle insulator
 Line post insulator
 Station post insulator
 Cut-out
 Pin Type Insulator
 As the name suggests, the pin type insulator is mounted on a pin on the
cross-arm on the pole.
 There is a groove on the upper end of the insulator.
 The conductor passes through this groove and is tied to the insulator
with annealed wire of the same material as the conductor.
 Pin type insulators are used for transmission and distribution of electric
power at voltages up to 33 kV.
 Beyond operating voltage of 33 kV, the pin type insulators become too
bulky and hence uneconomical.
 Suspension Insulator
 For voltages greater than 33 kV, it is a usual practice to use suspension
type insulators
 Consist of a number of porcelain discs connected in series by metal
links in the form of a string.
 The conductor is suspended at the bottom end of this string while the
other end of the string is secured to the cross-arm of the tower.
 The number of disc units used depends on the voltage.
 Strain Insulator
 A dead end or anchor pole or tower is used where a straight section of
line ends, or angles off in another direction.
 These poles must withstand the lateral (horizontal) tension of the long
straight section of wire.
 In order to support this lateral load, strain insulators are used.
 For low voltage lines (less than 11 kV), shackle insulators are used as
strain insulators.
 However, for high voltage transmission lines, strings of cap-and-pin
(disc) insulators are used, attached to the crossarm in a horizontal
direction.
 Shackle Insulator
 In early days, the shackle insulators were used as strain insulators.
 But now a day, they are frequently used for low voltage distribution
lines.
 Such insulators can be used either in a horizontal position or in a
vertical position.
 They can be directly fixed to the pole with a bolt or to the cross arm.
 Conductor
 Conductor is an object or type of material that permits the flow
of electrical current in one or more directions.
 For example, a wire is an electrical conductor that can carry
electricity along its length.
 Cont….
 Requirements of good conductor:
Good conductivity or low specific resistance
High tensile strength to withstand mechanical stresses
Not brittle
Not too expensive
Low specific gravity for low weight
 Materials may be:
 Copper
 Aluminum
 ACSR ( Aluminum conductor steel core reinforced
 Galvanized steel
 Phosphor bronze
 Cadmium copper
Cont….
 Lightning Arresters
 Lightning arrester is a device used on electrical power systems and
telecommunications systems to protect the insulation and conductors
of the system from the damaging effects of lightning.
 The typical lightning arrester has a high-voltage terminal and a ground
terminal.
 When a lightning surge (or switching surge, which is very similar)
travels along the power line to the arrester, the current from the surge
is diverted through the arrestor, in most cases to earth.
 Wire Sizes
 In the United States, it is common practice to indicate wire sizes by gage
numbers.
 The source of these numbers for electrical wire is the American Wire
Gage (AWG) (otherwise known as the Brown & Sharpe Gage).
 A small wire is designated by a large number and a large wire by a small
number
 Cut out
 Fuse cutout or cut-out fuse is a combination of a fuse and a
switch, used in primary overhead feeder lines and taps to
protect distribution transformers from current surges and overloads.
 An overcurrent caused by a fault in the transformer or customer
circuit will cause the fuse to melt, disconnecting the transformer from
the line.
 It can also be opened manually by utility linemen standing on the
ground and using a long insulating stick called a "hot stick".
 Transformers
 Transfers energy between two or more circuits through electromagnetic
induction.
 Phone/Cables Wires
 These wires were typically copper, although aluminium has also been
used, and were carried in balanced pairs separated by about 25 cm
(10") on poles above the ground, and later as twisted pair cables.
 Modern lines may run underground, and may carry analog or digital
signals to the exchange, or may have a device that converts the analog
signal to digital for transmission on a carrier system.
 Grounding
 Electrical circuits may be connected to ground (earth) for several
reasons.
 In mains powered equipment, exposed metal parts are connected to
ground to prevent user contact with dangerous voltage if electrical
insulation fails.
 Connections to ground limit the build-up of static electricity when
handling flammable products or electrostatic-sensitive devices.
 Guy wire
 A guy-wire or guy-rope, also known as simply a guy, is a tensioned
cable designed to add stability to a free-standing structure.
 They are used commonly in ship masts, radio masts, wind turbines,
utility poles, fire service extension ladders used in church raises and tents.