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Here is a compilation of essays on ‘Small Hydro Power Plants’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Small Hydro Power Plants’ especially written for school and college students.
Essay on Small Hydro Power Plants (SHP)
Essay Contents:
- Essay on the Introduction to Small Hydro Power Plants (SHP)
- Essay on the Main Elements of Small Hydro Power Plants
- Essay on the Different Site Layouts of Small Hydro Power Plants
- Essay on the Turbines in Small Hydro Power Plants
- Essay on the Power in Small Hydro Power Plant
- Essay on the Efficiency of Small Hydro Power Plants
- Essay on the Governors used in Small Hydro Power Plants
- Essay on the Specification of Turbine, Generator and Governor System used in Small Hydroelectric Power Plant
- Essay on the Advantages and Shortcomings of Small Hydroelectric Power Plants
- Essay on the Shortcomings of Small Hydro Power Plants
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Essay # 1. Introduction to Small Hydro Power Plants (SHP):
Hydro-energy is the most reliable and cost effective renewable energy source. Small hydro-power system play a major role in meeting power requirement of remote, isolated hilly areas in a de-centralized manner by tapping water stream, rivulets and canals of small discharge.
It captures the energy in flowing water and converts it into electricity. Small hydro projects are environment friendly, have relatively short gestation periods and require small investment as compared to large hydro projects.
In particular, the key advantages that small hydro has over wind, wave and solar power are:
i. A high efficiency (70 – 90%), by far the best of all energy technologies.
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ii. A high capacity factor (typically >50%), compared with 10% for solar and 30% for wind.
iii. A high level of predictability, varying with annual rainfall patterns.
iv. Slow rate of change; the output power varies only gradually from day to day (not from minute to minute).
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v. A good correlation with demand.
vi. It is a long-lasting and robust technology; systems can readily be engineered to last for 50 years or more. It is also environmentally benign. Small hydro is in most cases ‘run-of-river’; in other words any dam or barrage is quite small, usually just a weir, and little or no water is stored. Therefore run-of-river installations do not have the same kinds of adverse effect on the local environment as large-scale hydro.
Global installed capacity of small hydro is around 47000 MW against the estimated potential of 2,00,000 MW. India has a history of more than 100 years in small hydro. An estimated potential of 15,000 MW of small hydro exists in India. However, nearly 5000 MW have been actually identified through more than 2000 sites in 13 states of India and most of the sites are located in Himalayan region.
Himalayan region is endowed with one of the world’s largest water resources mostly rain and snow fed rivers, rivulets and streams with perennial flows. The mountainous hilly regions in the Himalayan belt suffer from the general impediments of difficult terrain, poor accessibility, poor transportation and poor communication facilities. The villages are predominantly tribal and are scattered over large mountainous hilly areas.
A lot of work has already been done by Rural Electrification Corporation (REC) to electrify these tribal villages. The problem of rural electrification is a peculiar one especially in the mountainous regions of Himalayas.
The laying of transmission lines across these regions poses a stupendous problem because of the long distances to be covered and the existence of hills and valleys, mountains, ridges, etc. As such, the process of laying transmission lines from the existing grid network becomes an extra-ordinarily costly proposition.
What is more, the problem is not entirely solved by laying of these lines. Up keep of the lines is also an equally tough job in view of the frequent occurrences of storms, snow falls, land-slides, ice formation, avalanches, etc. For such hilly regions diesel generating sets are also no answer, as the transportation cost of the fuel is prohibitive.
Thus for such mountainous areas there is no other choice than to depend on Decentralized. Renewable sources of energy of which SHP is the first option because of its higher energy intensity and availability in the region. Obviously therefore, most of the SHP development in the beginning has taken place in the Himalayan region. The first SHP station in India was a 130 kW plant installed at Sidrapong, Darjeeling in 1897.
The estimated potential of small hydro in the country is of about 15,000 MW. The aim is that out of the total grid interactive power generation capacity that is being installed, 2% should come from small hydro. The Indian SHP development program received a new dimension and tempo after the liberalization of economy and invitation to private sector for investment in power.
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Today the SHP program is essentially private investment driven. Electricity generation from small hydro is becoming increasingly competitive with preferential tariffs and some other concessions. The challenge is to improve reliability, quality and reduce costs. The focus of the SHP program is to lower the cost of equipment, increase its reliability and set up projects in areas which give the maximum advantage in terms of capacity utilization.
Hydropower is a renewable, non-polluting and environmentally benign source of energy. It is perhaps the oldest renewable energy technique known to the mankind for mechanical energy conversion as well as electricity generation. Hydropower represents use of water resources towards inflation free energy due to absence of fuel cost with mature technology characterized by highest prime moving efficiency and spectacular operational flexibility.
Hydropower contributes around 22% of the World electricity supply generated from about 7,50,000 MW of installed capacity and in many countries, it is the main source of power generation, e.g. Norway – 99%, Brazil- 86%, Switzerland – 76% and Sweden – 50%.
Essay # 2. Main Elements of Small Hydro Power Plants:
SHP plant generates electricity or mechanical power by converting the power available in flowing water of rivers, canals and streams. The objective of a hydropower scheme is to convert the potential energy of a mass of water flowing in a stream with a certain fall, called 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. A well designed SHP system can blend in with its surroundings and have minimal negative environmental impacts.
The main elements of SHP are:
i. Water is taken from the river by diverting it through an intake at a weir.
ii. In medium or high-head installations water may first be carried horizontally to the fore bay tank by a small canal.
iii. Before descending to the turbine, the water passes through a settling tank or ‘fore bay’ in which the water is slowed down sufficiently for suspended particles to settle out.
iv. The fore bay is usually protected by a rack of metal bars (a trash rack) which filters out water-borne debris.
v. A pressure pipe, or ‘penstock’, conveys the water from the fore bay to the turbine, which is enclosed in the powerhouse together with the generator and control equipment.
vi. After leaving the turbine, the water discharges down a ‘tailrace’ canal back into the river.
SHP schemes are mainly run-of-river with little or no reservoir impoundment. Schematic layout of a SHP plant is shown in Fig. above.
Essay # 3. Different Site Layouts of Small Hydro Power Plants:
In practice, sites that are suitable for small-scale hydro schemes vary greatly. They include mountainous locations where there are fast-flowing mountain streams and lowland areas with wide rivers. In some cases development would involve the refurbishment of a historic water power site. In others it would require an entirely new construction.
A variation on the canal-and-penstock layout for medium and high-head schemes is to use only a penstock, and omit the use of a canal. This would be applicable where the terrain would make canal construction difficult, or in an environmentally-sensitive location where the scheme needs to be hidden and a buried penstock is the only acceptable solution.
Essay # 4. Turbines in Small Hydro Power Plants:
A turbine unit consists of a runner connected to a shaft that converts the potential energy in falling water into mechanical or shaft power. A turbine and generator unit is shown in Fig. 1.30.
Turbines can be crudely classified as high-head, medium-head, or low-head machines. Electricity generation usually requires a shaft speed as close as possible to 1500 rpm to minimize the speed change between the turbine and the generator. Since the speed of any given type of turbine declines with head, low-head sites need turbines that are inherently faster under a given operating condition.
Turbines are also divided by their principle of operation and can be either impulse or reaction turbines. The rotor of the reaction turbine is fully immersed in water and is enclosed in a pressure casing. The runner blades are profiled so that pressure differences across them impose lift forces, just as on aircraft wings, which cause the runner to rotate.
In contrast an impulse turbine runner operates in air, driven by a jet (or jets) of water. The choice of the turbines depends mainly on the head and the design flow for the SHP installation. All turbines have power-speed characteristics. They will perform most efficiently at a particular speed, head and flow combination.
The detail of these two types of turbines is as follows:
a. Impulse Turbines:
There are 3 main types of impulse turbine in use- the Pelton, the Turgo, and the Cross flow turbines. The Pelton Turbine consists of a wheel with a series of split buckets set around its rim; a high velocity jet of water is directed tangentially at the wheel. The jet hits each bucket and is split in half, so that each half is turned and deflected back almost through 180°.
Nearly all the energy of the water goes into propelling the bucket and the deflected water falls into a discharge channel below. The Turgo turbine is similar to the Pelton but the jet strikes the plane of the runner at an angle (typically 20°) so that the water enters the runner on one side and exits on the other.
Therefore the flow rate is not limited by the discharged fluid interfering with the incoming jet (as is the case with Pelton turbines). As a consequence, a Turgo turbine can have a smaller diameter runner than a Pelton for an equivalent power. The Cross flow turbine has a drum-like rotor with a solid disk at each end and gutter-shaped ‘slats’ joining the two disks.
A jet of water enters the top of the rotor through the curved blades, emerging on the far side of the rotor by passing through the blades a 2nd time. The shape of the blades is such that on each passage through the periphery of the rotor the water transfers some of its momentum, before falling away with little residual energy.
b. Reaction Turbines:
The two main types of reaction turbine are the propeller (with Kaplan variant) and Francis turbines. Reaction turbines exploit the oncoming flow of water to generate hydrodynamic lift forces to propel the runner blades. They are distinguished from the impulse type by having a runner that always functions within a completely water-filled casing.
All reaction turbines have a diffuser known as a ‘draft tube’ below the runner through which the water discharges. The draft tube slows the discharged water and reduces the static pressure below the runner and thereby increases the effective head. Propeller-type turbines are similar in principle to the propeller of a ship, but operating in reversed mode.
Various configurations of propeller turbine exist; a key feature is that for good efficiency the water needs to be given some swirl before entering the turbine runner. With good design, the swirl is absorbed by the runner and the water that emerges flows straight into the draft tube. Methods for adding inlet swirl include the use of a set of guide vanes mounted upstream of the runner with water spiraling into the runner through them.
Another method is to form ‘snail shell’ housing for the runner in which the water enters tangentially and is forced to spiral in to the runner. When guide vanes are used, these are often adjustable so as to vary the flow admitted to the runner.
In some cases the blades of the runner can also be adjusted, in which case the turbine is called a Kaplan. The mechanics for adjusting turbine blades and guide vanes can be costly and tend to be more affordable for large systems, but can greatly improve efficiency over a wide range of flows.
The Francis turbine is essentially a modified form of propeller turbine in which water flows radially inwards into the runner and is turned to emerge axially. For medium-head schemes, the runner is most commonly mounted in a spiral casing with internal adjustable guide vanes.
The Francis turbine was originally designed as a low-head machine, installed in an open chamber without a spiral casing. Thousands of such machines were installed in the UK and the rest of Europe from the 1920s to the 1960s.
Although an efficient turbine, it was eventually superseded by the propeller turbine which is more compact and faster-running for the same head and flow conditions. However, many of these ‘open-flume’ Francis turbines are still in place, hence this technology is still relevant for refurbishment schemes.
Essay # 5. Power in Small Hydro Power Plant:
A hydro power resource can be measured according to the amount of available power or energy per unit time. The power of a given situation is a function of head and rate of flow. Hydraulic power can be captured wherever a flow of water falls from a higher level to a lower level. This may occur where a stream runs down a hill side or a river passes over a waterfall or man-made weir, or where a reservoir discharges water back into the main river.
The vertical fall of the water, known as the ‘head’, is essential for hydropower generation; fast-flowing water on its own does not contain sufficient energy for useful power production except on a very large scale, such as offshore marine currents. Hence two quantities are required: a Flow Rate of water Q, and a Head H. It is generally better to have more head than more flow, since this keeps the equipment smaller.
The Gross Head (H) is the maximum available vertical fall in the water, from the upstream level to the downstream level. The actual head seen by a turbine will be slightly less than the gross head due to losses incurred when transferring the water into and away from the machine. This reduced head is known as the Net Head.
The Flow Rate (Q) in the river is the volume of water passing per second, measured in m3/sec. For small schemes, the flow rate may also be expressed in liters/second where 1000 liters/sec is equal to 1 m3 /sec.
Energy is an amount of work done, or a capacity to do work, measured in Joules. Electricity is a form of energy, but is generally expressed in its own units of kilowatt-hours (kWh) where 1 kWh = 3,600,000 Joules and is the electricity supplied by 1 kW working for 1 hour.
Power is the energy converted per second, i.e. the rate of work being done, measured in watts (where 1 watt = 1 Joule/sec. and 1 kilowatt = 1000 watts). Hydro-turbines convert water pressure into mechanical shaft power, which can be used to drive an electricity generator, or other machinery. The power available is proportional to the product of head and flow rate.
The energy in a SHP starts out as potential energy by virtue of its height above the powerhouse as shown in Fig. 1.34. Water under pressure in the penstock is able to do work when released so there is energy associated with the pressure as well. The transformation of energy is from potential to pressure to kinetic energy.
Energy head per unit mass = z + P/γ + y2/2g …(1)
Where z – elevation from a reference height (m) P – pressure (Nm-2)
γ – Specific weight (Nm-3) (density of water:
v – Average velocity (ms-1)
g – Gravitational acceleration (9.81 ms2)
The power theoretically available from a site is proportional to the difference in elevation between the source and the turbine, called the head H, times the rate at which water flows from one end (height) to the other,
Power = Energy/Time = Weight/Volume × Volume/Time × Energy/Weight = γ.Q.H
The power (in watt) delivered from the nozzle at the end of penstock is P = γ.Q.HN, where HN is the net head (Gross head – head loss – HG – ΔH). The power in kW from the nozzle is
Pi(kW) = γ.Q.HN /1000= 9.81.Q.HN
From above equation one can see that the power in the hydropower system strongly depends on the net head and the flow rate of water. SHP sites are characterized as high head or low head. The higher the head the better it is because then one would need less water {i.e., less flow rate) to produce a given amount of power.
Essay # 6. Efficiency of Small Hydro Power Plants:
Efficiency of the SHP plant depends upon the efficiency of turbine, generator and transformer.
The final power (Pf) output from SHP is smaller than available hydraulic power (Pi)
Pi = ηP
That is
Pf (kW) = (9.81).η.Q.H
Where η is the overall efficiency, which is given as:
η = ηturbine . ηgenerator . ηtransformer
η = ηturbine – 60-95% This depends on the type of turbine used.
ηgenerator – 75-90% This depends on the size of the generator.
ηtransformer – 80-95% This depends on the size of the transformer.
Essay # 7. Governors used in Small Hydro Power Plants:
With the vast use of hydro power, especially the small hydro which are mostly de centralized, control of power is of utmost importance. In an electric power system, consumers require power at rated frequency and voltage.
To maintain these parameters under permissible limits, some controls are required in the power system at generation level. Voltage is maintained by controlling the excitation voltage of the alternator; while frequency is maintained within permissible limit by speed control of turbines according to the load variation.
To maintain the generator at a constant 50 Hz frequency, it is necessary to maintain the generator shaft at a constant rotational speed. In the independent hydroelectric power plant, the rotational speed of the small hydro power generator can be changed when loads are added or subtracted from the electrical system.
Frequency of generated voltage and generator shaft speed are related as:
The system frequency can be maintained constant by eliminating the mismatch between generator and load. Governor is used to control the speed of shaft as per the load requirement. Governor controls the water flow to the turbine as per the load requirement.
Conventional governor systems can be classified as mechanical hydraulic governors, electro hydraulic governors or mechanical types. Mechanical hydraulic governors are sophisticated devices which are generally used in large hydro power systems.
They require heavy maintenance and are expensive to install, making their usage in small hydro power plants uneconomical. Electro hydraulic governors are complex devices needing precision design and are expensive.
Mechanical governors incorporate a massive fly ball arrangement and usually do not provide flow control. They require an elaborate set of complex guide vanes, inlet valves and jet deflectors. Conventional governing systems therefore, because of their cost and complexity, are not ideally suited for isolated, small hydro power plants that are not grid connected. The current trend is therefore to use load side regulation.
For isolated type small hydro power plants, electronic load controllers (ELCs) have been developed that have increased the simplicity and reliability of SHP system. An ELC is a solid-state electronic device designed to regulate output power of SHP systems. Maintaining a near-constant load on the turbine generates stable voltage and frequency.
The controller compensates for variation in the main load by automatically varying the amount of power dissipated in a resistive load, generally known as the ballast or dump load, in order to keep the total load on the generator and turbine constant. Water heaters are generally used as ballast loads.
An ELC constantly senses and regulates the generated frequency. The frequency is directly proportional to the speed of the turbine. The major benefit of ELCs is that they have no moving parts, are reliable and virtually maintenance free. But this method has a biggest disadvantage as this system has no flow regulating devices and their governor control system.
Load controllers however waste precious energy which could have otherwise been used gainfully. Also they do not carry out flow control implying that mineral rich water is made to spill away which could have been diverted at high head for other applications such as irrigation purposes.
Another type of Governor used in Small Hydro Power plants for controlling the water flow to the hydro turbine involves Spear valve and servomotor which gets controlling signal from PID controller. Spear valve is used for continuous flow control. Servomotor is used as the governor which operates the spear valve for flow control.
Governor compares the frequency signal obtained from the output of the generator, with the standard frequency signal and controls the spear valve. The spear valve in turn controls the flow of water into the turbine. To further getting the better control various soft computing techniques such as artificial neural network and fuzzy logic, etc., can be applied to optimize the tuning of PID parameters.
In recent times, most of the small hydro power plants use newly developed governor composed of standard hydraulic equipment with digital control technology and hydraulic integrated technology involving digital valve and PLC. Programmable controller and relative modules are used as kernel of the governor for control.
The technology of variable structure and parameter PID and pulse width modulation is used in the speed governing system with functions of self-diagnosis, fault prevention, tolerance and correction. With this system, the rapid and accurate speed governing, including automatic and manual start and stop of the hydro-electric generating unit and emergency stop can be achieved to get the safe and stable operation of the plant.
The touch screen and the man -machine interface make the operation of governor simple and easy. The design of advanced hydraulic integration is used. The standard digital valve is used for electrical/hydraulic conversion. The interface facility with computer is also provided.
Essay # 8. Specification of Turbine, Generator and Governor System used in Small Hydroelectric Power Plant:
Apart from hundreds of equipment used in the whole set up of Small Hydroelectric Power Plant, the turbine, generator and governor system are installed inside power house.
E.g., A 5 MW capacity plants having two units of 2.5 MW capacity each and grid connected type has the turbine and generator having following specification:
Also a view Mini Hydroelectric Power Plant of 2 MW capacity having two units of 1 MW each under operating condition located near Chamba town in Himachal Pradesh is as shown below:
Essay # 9. Advantages and Shortcomings of Small Hydroelectric Power Plants:
Some of the key advantages of SHP are:
i. Environmental protection through CO2 emission reduction – CO2 emission is reduced because electricity production from SHP does not release CO2 in the process.
ii. Proven and reliable technology
iii. Improves the diversity of energy supplies – this is the one of many alternatives of producing electricity.
iv. Grid stability
v. Reduced land requirements – unlike in wind energy, fair bit of land is required to install a wind turbine.
vi. Local and regional development – leads the community to be independent of fossil fuel.
vii. Assists in the maintenance of river basins
viii. Technology suitable for rural electrification in developing countries
ix. High energy payback ratio
Essay # 10. Shortcomings of Small Hydro Power Plants:
Some of the shortcomings are:
i. SHP is a site specific technology and usually the site is far away from the place where the electricity is required
ii. Run-of-river plants experience significant fluctuations in output power.