Microsoft Power Point - d.02 Turbine Selection En

8/8/2019 Microsoft Power Point - d.02 Turbine Selection En

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ASEAN-German Mini Hydro Project (AGMHP)

Consulting and Engineering

Selection of

Turbines

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Turbines

Various turbine types are used in SHP. Their selectionbasically depends on the head / flow conditions of asite.

As a general rule, impulse turbines such as Pelton are used for high

head and relatively low flow systems, propeller turbines (Kaplan, tube, bulb, S) are used for

low head and high flow applications. Francis and cross-flow turbines are available for low

to medium head sites.

Electro-mechanical Equipment


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turbine application ranges

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turbine application ranges


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Typical impulse turbine, where the available head isconverted into kinetic energy before the runner.

Turbine consists of a runner with a number of bucketson which one or more water jets impinge.

Flow and hence power output is adjusted by a needlevalve which can increase or decrease the nozzleopening.

For higher flows the number of jets can be increased(up to six for SHP).

Highly efficient turbine also for part-flow operation downto 10 % of design flow.

By installing a jet deflector the pressure surge in thepenstock can be avoided.

Pelton Turbine

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Pelton Turbine


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Pelton Turbine

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The cross-flow turbine is also regarded as an impulseturbine, although the free jet impinging the runner isnot as pronounced as with the Pelton.

Cross-flow turbines are very robust and relativelysimple machines and are therefore highlyrecommended for rural electrification where operatorsmight be limited in availability of skills and

maintenance support. The efficiency of cross-flow turbines (up to 80%) is

lower compared to other turbine types.

Crossflow Turbine


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crossflow turbine

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crossflow turbine


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The Francis turbine is the oldest and probably the best-known reaction turbine. In contrast to impulse turbines, therunner in reaction turbines is completely submerged in thewater.

The runner consists of a row of curved blades which formchannels through which the water is accelerated andredirected.

Regulation of flow is accomplished by a row of adjustableblades, the so-called wicket-gates or guide vanes, whichare arranged concentrically around the runner.

For very low head applications (< 10 m), Francis turbinescome in the form of open flume or pit-type machines. Forhigher heads up to 200 m, spiral casings are used.

Francis Turbine

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Francis Turbine (spiral casing, horizontal shaft)


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Francis Turbine (spiral casing, horizontal shaft)

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Propeller turbines are also reaction turbines, but flowpasses through the runner in axial direction with littleto no inward deflection.

The oldest propeller type turbine is the Kaplan with ascroll or spiral casing and radial wicket gateconfiguration for flow regulation similar to the Francis.

The classic Kaplan has both adjustable blades and

adjustable wicket gates which gives best efficienciesover a wide range of flow rates.

Propeller turbines are also available in the form oftube, bulb and S-turbines.

Propeller-type Turbines


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Kaplan Turbine

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s-type propeller turbine


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Propeller Turbine

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As a general rule, the number of turbines should be kept aslow as possible, i.e., between 1 and 3, in SHP development.

The need to install more than one turbine arises with avariable stream flow (or load in stand-alone systems) with aratio of design flow to minimum flow of more than 2 to 3 forFrancis and propeller machines, and more than 5 to 10 forPelton and cross-flow machines.

As flows (or loads) vary in ratios of more than 3 for most

SHP installations, it becomes clear that Francis andpropeller turbines are not ideal for SHP, and single cross-flow units often tend to be more cost-effective than Francismachines despite the lower peak efficiencies of the cross-flow.

Number of Turbine Units


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The speed of the turbine in a SHP installation needs to bekept constant in order that the driven generator can produceelectricity of standard quality, i.e., frequency of 50 Hz.

In grid connected systems the leading parameter is poweroutput of the turbine and the corresponding water flow.Generator load is not critical because almost any output canbe absorbed by the grid.

Usual practice today is to monitor forebay/storage waterlevels with a level sensor and adjust turbine flow

automatically using electric servo motors (linear actuators)or oil-hydraulically operated devices acting on nozzle orguide vanes.

Turbine Speed Controlling -- on-grid system

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In stand-alone systems, turbine speed control is morecomplicated because the power absorbed by the load centeris the decisive element and not the water availability.

Conventional governors sense a deviation of speed from thenominal value and adjust nozzle or guide vane openingsaccordingly.

In stand alone systems rapid load changes may occur andflow control becomes very demanding. The installation of a

flywheel can ease such problems to some extent. Load controllers (for plants


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Electronically controlled systems have taken over from thetraditional oil-hydraulic governors because of cost reductionpotentials and because with electronic systems, turbinespeed governing can be more easily incorporated into othercontrol, monitoring and protection systems of SHP plants.

The main disadvantages of electronic control systems are:

Electronic components used for controllers becomeoutdated in a relatively short period of time which may beshorter than the expected service life of an SHP plant(> 20 years).

Lightning strikes have reportedly damaged wholeelectronic systems of SHP plants and only equipment withproven protection systems should be selected.

Electronic Turbine Control Systems

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Modern synthetic flat belts are capable of transmitting upto 500 kW of power at highest efficiencies (0.96 to 0.98).Gearing ratios are up to 5 for flat belts.

For higher power ranges and gearing ratios, gear boxesare used. These require less space than flat belts butare expensive and are not maintenance free (oil change,wear and eventual replacement of bearing and gears).

V-belts are readily available and need not as precisealignment of the machinery as flat belts or gear boxesbut are very limited in power transmission capacities andare therefore hardly used in SHP.

Gear Boxes and Couplings

Microsoft Power Point - d.02 Turbine Selection En

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