functioning of small hydro project

8/7/2019 functioning of small hydro project

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Functioning of a hydroelectric power plant

Hydroelectricity is one of the main forms of energy in use today. Its use is being

promoted in many countries of the world as a renewable and non-polluting source

of energy. The industrialized nations of the world have drawn flak in recent times

for releasing high concentrations of green house gases into the atmosphere. The

regulations of the Kyoto Protocol are making things tougher. Hence greater interest

is being shown in making use of non-polluting energy sources.

Hydroelectricity is produced in a hydroelectric power plant. In this plant, the water

is released from a high location. The potential energy present in the water is

converted into kinetic energy, which is then used to rotate the blades of a turbine.

The turbine is hooked to the generator which produces electricity.

The main components of hydroelectric power plant are:

a) The reservoir:Water from a natural water body like a river is stored in the

reservoir. This reservoir is built at a level higher than the turbine.

b) The dam: The flow of water stored in the reservoir is obstructed by huge walls

of the dam. This prevents the water from flowing and helps us harness the energy

present in it. The dam consists of gates present at its bottom, which can be lifted to

allow the flow of water through them.

c) The penstock: This connects the reservoir with the turbine propeller and runs in

a downward inclined manner. When the gates of the dam are lifted, the force of

gravity makes the water flow down the penstock and reach the blades of the

turbine. As the water flows through the penstock, the potential energy of water

stored in the dam is converted into kinetic energy.

d) The turbine: The kinetic energy of the running water turns the blades of the

turbine. The turbine can be either a Pelton Wheel Model or a Centrifugal type. The

turbine has a shaft connected to the generator.

e) The generator: A shaft runs from the turbine to the generator. When the blades

of the turbine rotate, the shaft turns a motor which produces electric current in the

generator.


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)

Water conductor system (broadly civil structures

Major components of a hydro electric project

1.1 Dams

The most important aspect of hydro power generation is to ensure that the plant

continue to function continuously. The main component of hydro power project is

dam, which may be concrete gravity, rock filled, earthen or combination of some

of above types. Earthen dams differ from masonry and concrete dams due to

relatively greater deformability and higher permeability of earth masses (excluding

plastic clay hearting). As these dams are big in general, The safety of the dams is

most vital for the unhindered performance of the power plant.

1.1 Barrage

The diversion structure like barrage and weir are generally designed on the

principle governing the percolating of water below the foundation of the structure.

The floor of the structure is suitably designed either as a raft of gravity section to

be safe against the uplift pressures created.

1.2 Water intake structure


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A structure to divert the water to waterway, which includes trash racks, a gate and

an entrance to a canal, penstock directly to turbine depending on the structure of

the project.

1.3 Head race tunnel/Power channel

A canal, tunnel and/or penstock carries the water to the power house. Sometimes a

desilting chamber precedes the head race tunnel, which remove the larger size

sediments from entering into the tunnel.

1.4 Surge shaft

Surge tank is provided into water conducting system primarily to reduce the surge

pressure to be considered in the designed penstock/ pressure shaft. This

economizes the design of penstock/ pressure shaft justifying the extra cost for the

provision of the surge tank. The provision of the surge tank has following

advantages:

y The length of the column of water gets reduce by placing a free watersurface close to the turbine.

y It act as a pressure relief opening to absorb surplus kinetic energy.y It acts as a balancing reservoir to supply/ store additional water during

starting/ closure of the gates/ valves.

A surge tank absorb the water hammer effects due to rapid start or closure of theturbine.

1.5 Penstock/ protection valves

The penstock valves are provided after the surge shaft to facilitate maintenance of

the penstock. These valves are butterfly valves. The are butterfly valves are

operated hydraulically with provision of pressure accumulated in case of power

failure.

1.6 Penstock/ pressure shaft

The penstock convey the water to the power house and can take many

configurations, depending upon the project layout. Where the power house is an

integrated part of the dam, the penstock is simply a passage through the upstream

portion of the dam. In case of project having long head race tunnel terminating in

the surge tank, the penstock from the surge tank, where most of drop in elevation


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occurs, would be a pressurerized tunnel or pipe. For multi unit installation, it is

often desirable to surve several units with a single penstock, and manifolds or

bifurcation structures are provided to direct the flow to individual units.

1.7 Main inlet valves (MIV)

These are spherical valves just provided before the water enter into the spiral

casing of the turbine. This is provided to stop the water for small maintenance

purpose In turbine hall.

1.8 Power House

Power house contains the electro mechanical equipment i.e. hydro power turbine,

Generator, excitation system, main inlet valves, transformers, Switchyard, DC

systems, governor, bus duct, step up transformers, step down transformers, high

voltages switch gears, control metering the protection systems.

2.0 Tail race (Tunnel/ channel)

The tail race tunnel or channel are provided to direct the used water coming out of

draft tube back to the river. The important criteria of designing the tail race tunnel/

channel is kind of draft tube, the gross head and geographical situation of the area.

Tail race is designed in such a way that water hammer is minimizes when water

leaves the draft tube.

Terminology related to small hydro project

3.1 Maximum Net Head

The gross head difference in elevation between the maximum head water

level and the tail water level with one unit operating at no load speed minus

losses.

3.2 Minimum Head ( Hmin )

The net head resulting from the difference in elevation between the

minimum head water level and the tail level minus losses with all turbines

operating at a specified gate opening.


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3.3 Rated Discharge

It is the volume in ms/second of water required by the turbine to ~generate

rated output while operating at rated head and speed.

3.4 Rated Speed

The speed in revolutions per minute at which the turbine operate to

generate the rated output under the rated head and discharge at a specified

gate opening.

4 TYPE OF SMALL HYDROELECTRICPOWER STATIONS

.

4.1 The small hydroelectric power stations are generally classified into

the following types:

Size Micro Mini Small

Unit Size Up to 100 kW 101 to 1 OOOkW 1001 to 5 000 kW

4.2 Head

For the purpose of this standard, following classification is adopted as

regards hydraulic head under which the turbine will operate

Medium/High head Above 40 metres

Low head Less than 40 metres

Ultra low head Below 3 metres

3.5 Rated Turbine Efficiency

The etficiency obtained at the rated head and rated discharge to obtain rated output.

3.6 Rated Turbine Output

The mechanical power delivered by the turbine shaft to generate rated output at

generator terminals. It is given by:


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5.2 Impulse Turbine

5.2.1 Turgo Impulse~Pelton Turbine

It has one or more free jets discharging into an aerated space and impinging

on the buckets of a runner. In Turgo impulse, the jet impinges on

several buckets continuously- wliereas only single bucket per jet is effective

at any instant in Pelton wheel. These may be mounted horizontally or

vertically.

5.2.2 Cross Flow Turbine

It is an impulse turbine with partial air admission. These are also called

Banki turbines.

5.3 Reaction Turbine

5.3.1 Francis Turbine

It has a runner with fixed vanes to which the water enters the turbine in a

radial direction with respect to the shaft and is discharged in an axial

direction. Steel plate/concrete water supply case or open flume are

used..Francis -turbines may be mounted with vertical or horizontal shafts.

5.3.2 Propeller Turbine -

It has a runner with blades in which water passes through the runner in an

axial direction with respect to the shaft. The pitch of the blades may be

fixed or movable. The conventional propeller of Kaplan ( variable pitch

blade ) turbine are mounted with a vertical,. horizontal or slant shaft.

5.3.3 Tubular Turbine .

It is hdrizontal or slant mounted with propeller runner. The generator islocated outside of the water passageway. These are equipped with fixed or

variable pitch runners and with or without gates assemblies.

5.3.4 Bulb Turbine.


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It is a horizantal unit which have propeller runners generally directly

connected to the generator. The generator is enclosed in a water tight

enclosure ( bulb ) located m the turbine water passageway. This is available

with fixed or variable pitch blades and with or without a wicket gate.

5.3.5 Rim Type Turbine

It is the one in which generator rotor is mounted on the periphery of the

turbine runner blades. lt is known as striaght flow turbine also, it is a small

bulb upstream, which houses the bearing. It is a horizontal unit.

6 CRITERIA FOR SELECTION OF HYDRAULIC TURBINE

6.1 Standardized Turbine

Type of turbines is selected from techno-economic considerations of

generating equipment, power house cost and relative advantages of power

generation. Most of the manufacturers have developed standardized turbine

designs which may be effectively employed. Standard design may lead to

cheaper and quicker construction. The factors given in 6.2 to 6.8 shall

determine the type of turbine to be used for any site conditions.

6.2 Head

Maximum net head acting on the turbine is one of the most important

criteria dictating type of turbine to be used for the power station under

consideration. Normal range of maximum net head with respect to power

output for each of the type of turbines is given in Fig. 1.

In overlapping head ranges more detailed analysis need to be carried out

with a view to optimize costs for selecting exact type of turbine.

6.3 Head Variations

Performance -of theturbine is ideal at design head. Turbine efficiency falls

at head higher and lower than the design head. Normal range of head

variations for various type of turbines is given in Table 1.

6.4 Load Variations


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Turbine efficiency varies with load. Necessity of operating turbine at part

loads influences choice of turbines in the overlapping head ranges. Minimum

load upto which the turbine may be operated without undue cavitation and

vibration is dictated by type of turbine and is given in Table 1.

FIG. 1 SUMMARY CHART OF COMMERCIALLY AVAILABLB

TURBINES


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Table 1: VARIOUS TURBINES AVAILABLE WITH THEIR SPECIFIC

SPEED

S. No. Type of Turbine Specific

Speed

Head Application

(m)

Min.

Max.

1. Pelton wheel 12-30 100 500

2. Turgo Impulse

(inclined pelton) 2 -7 4 23. Cross flow

-4. Francis

-5. Propeller and

Kaplan 340-1000 2 25

6.6 Turbine Setting and Excavation Requirement

Setting of reaction turbine with reference to minimum tail water is dictated by requirement from cavitational considerations. In general cavitation co-

efficient for


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Pt =rated turbme output in metric horse power ( equivalent to = 0.9863

horse power ) at full gate opening.

6.7.1 Runner Diameter

The actual runner size is determined by the manufacturer in accordance with

model tests and design criteria. For estimating purposes following formula

can be used.

Runner diameter

where s is the velocity ratio at discharge diameter of runner.

6.7.1.2 Propeller turbine

and Runner dia,

6.7.1.3 Impulse turbine

where

d = diameter of jet


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Practical values of

Normal diameter ratio is

6.8 Pressure Rise and Speed Regulation Considerations

This aspect is more important in isolated system because inertia of small

hydro machine is low. Low governor closmg time for better speed regulation

may be achieved by installing pressure relief valves. Speed regulation could

also be improved installing a flywheel. In units under micro range, electronic

controllers for speed regulation with phantom loads may be considered.

Pressure rise and speed rise may, therefore, be limited to vary economic

levels in case of Pelton turbines without increasing the cost of turbine.

8 POWER PLANT AUXILIARY EQUIPMENT AND APPURTENANT

FACILITIES

8.1 Space is to be provided in a power house for the following auxiliary

equipment and appurtenant facilities as required:

Turbine governor and shut off valve,

Generator breakers,

Unit and auxiliary power transformers,

Control cubicle and relaying equipment,

Neutral grounding cubicle and surge ,protection,

Station battery,

Cooling water system,

Drainage and dewatering system,

Ventilation,


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Fire extinguishers,

Compressed air system, and

Temporary or permanent crane.

Power House

Power House is a building to house the turbines, Generators and other accessories

for operating the machines.

Components ofPower House

A. Mechanical Component

Distributor/Spiral Casing- a casing or housing used to distribute the water

equally all along the periphery of runner.

Spherical valve or Main Inlet Valve- Valve used to isolate the turbine or machine

from water incase non-availability of water for generation or maintenance

Turbine; a hydromachine used to convert the hydraulic energy to mechanical

energy

EOT Crane(Electric Overhead Crane);used to lift the equipment of the power

house viz., rotor (heaviest component in the power station), stator, shafts, runner

and other equipment

B. Electrical Component

Generator; machine used to convert the mechanical energy into electrical energy

Transformers; to step up the generation voltage upto the capacity of grid

Switchyard; is the central protection and metering of the outgoing feeders after

stepping up of system voltage using transformer (usually consist of Circuit

Breakers, Isolators, disconnect switch, Current transformer, Potential transformer,

lighting arrestors etc)


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Circuit Breakers: to disconnect the system in case of faults vis--vis short circuit,

over voltage, under voltage, under frequency, distance faults etc

Disconnect switch/Isolators: to open the circuit as & when desired to take up the

system for maintenance

Current Transformer: to step down the system current to the level of 1A/ 5A as

the case may be. Used for current measurement and power measurement

Potential Transformer: for Power and voltage measurement

Communication system: consist of wave trap and PLCC for data transfer through

power lines.

Transmission lines: using transmission line tower the power is transferred from

the generating station to the nearest grid (of desired capacity) General rating of the

lines are 11kV ,33kV, 66kV, 132 kV, 220 kV, 400 kV, 750/800 kV.

C. Power House Auxiliaries

Cooling Water system: used to supply the cooling water to Generator air coolers,

Turbine bearing, Generator bearing, transformer cooling etc.,

Compressed Air System: used to supply compressed air to various turbine and

generator auxiliaries for rotor lifting, generator brakes, service air etc.,

De- watering System: used to de-water the powerhouse in case of seepage,

maintenance etc., also used for de-watering the tunnel, penstock.

Air conditioning and ventilation:used to maintain the normal working

temperature inside the control room and powerhouse building for efficient working

of equipment and operating staff.

Fire protection and detection systemsthis system is used to protect each

Generating equipment and its auxiliaries of the powerplant against the fire hazards.

Also, for insurance coverage this system is must and TAC (Terrific Advisory

Committee) norms has to be follow for his approval.


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Drainage system: used to drain water from powerhouse used for cleaning, water

close-let, drinking water etc.

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functioning of small hydro project