Hydroelectric Power Generation notes (publication by electroogle.blogspot.com)

8/7/2019 Hydroelectric Power Generation notes (publication by electroogle.blogspot.com)

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Electroogle.blogspot.com

By Usmanumar



Hydroelectric PowerGenerationINTRODUCTION:

Hydroelectric power generation involves the storage of a hydraulic liquid, water, conversion of thehydraulic (potential) energy of the liquid into mechanical (kinetic) energy in a hydraulic turbine, andconversion of the mechanical energy to electrical energy in an electric generator.

Reffered to as WHITE COALfor its power and plenty First hydroelectric power plant came into service in the 1880s Now comprising 30% of the world’s installed generation capacity Largest dam is THREE GORGES DAM having a capacity of 22,500 MW

EXPLANATION:

The water in rivers posses two types of energies: kinetic energy and potential energy.The energy of water due to its motion is calledas kinetic energy . The energy of water due toits high level is called as potential energy .Depending on the type of hydraulic powerplants kineticor potential energy of water isused to generate electricity.

The large quantities of water from river are

diverted by pipelines also called as penstock ,towards the main plant where large turbinesare located. The water from penstock isallowed to fall on the large turbine blades thatstart rotating. The shaft of the turbine rotatesin the electric generators where electricity isgenerated. This electricity is then passed to thetransformers from where it is connected to the

main national grid.The water leaving the turbine flows back to the river at the lower levels

ADVANTAGES:

Quick to start up(Approx 5 mins) , loading , unloading & following of system variations Low operating and maintenance cost (Economical) Provides flexibility in base loading , peaking and energy storage applications Long service life High reliability Black start capability



Flood Control Used for irrigation

BASIC PURPOSE OF DAMS ARE TO CONTROL FLOOD AND FOR IRRIGATION NOT TO GENERATEELECTRICITY

DISADVANTAGES:

High initial capital cost required Loss of land (land per mega watt is very large) Installation period is large(aprox 5-8 years) Eco-system damage Flow shortage Relocation Failure hazard

Siltation

TYPES OF POWER PLANTS (Sizes and capacities of hydroelectric facilities):

LARGE HYDRO No official definition Ranges from few hundered Megawatts (approx 30 Mw) to more than 10 GW Three large dams of the world (Three gorges dam – 22.5 Gw)(Itapiu dam – 14 Gw)

(Guri dam – 10.2 Gw) Disadvantage (larger affects on environment)

SMALL HYDRO Upto 30 Mw Total world small hydro capacity = 85 Gw Production grews by 28% during 2005-2008

MICRO HYDRO Upto 100 Kw Can provide power to isolated home , small community

PICO HYDRO Under 5 Kw Small turbines of 200-300 W can provide a home with a drop of only 1m(3 ft) Typically are run-off river



PLANNING OF HYDRO ELECTRIC FACILITIES SITING

Hydro electric plants are located in geographic areas where they will make economic use of

hydraulic energy sources The majority of sites utilize the head developed by freshwater; however, other liquids such assaltwater and treated sewage have been utilized

The siting of a prospective hydroelectric requires careful evaluation of technical, economic,environmental (wild life , eco-system), and social factors (relocation)

HYDRO ELECTRIC PLANT SCHEMES (CLASSIFICATION)

There are four main types of hydroelectric plant arrangements, classified according to themethod of controlling the hydraulic FLow at the site :

Run-of-the-river plants , having small amounts of water storage and thus little control of the flow through the plant

Storage plants , having the ability to store water and thus control the flow through theplant on adaily or seasonal basis

Pumped storage plants , in which the direction of rotation of the turbines is reversedduring off-peak hours, pumping water from a lower reservoir to an upper reservoir, thus‘‘storing energy’’ for later production of electricity during peak hours

Cascaded plants, a series of Power plants (one after another)

SELECTION OF PLANT CAPACITY, ENERGY, AND OTHER DESIGN FEATURES

POWER CALCULATION

The power available from falling water can be expressed as

= ρ q g h e

where

Pth = power theoretically available (W)ρ = density (kg/m3) (~ 1000 kg/m3 for water)q = water flow (m3/s)g = acceleration of gravity (9.81 m/s2)h = falling height, head (m)e= coefficient of efficiency ranging from 0 to 1

Due to energy loss the practically available power will be less than the theoretically power.



DESIGN FEATURES

Flow rate and head are influenced by reservoir inflow, storage characteristics, plant andequipment design features, and flow restrictions imposed by irrigation, minimum downstreamreleases, or flood control requirements

Historical daily, seasonal, maximum ( flood), and minimum (drought) flow conditions arecarefully studied in the planning stages Physical features such as the dam and spillway structures are optimized through complex

economic studies that consider the hydrological data, planned reservoir operation,performance characteristics of plant equipment, construction costs, the value of capacityand energy, and financial discount rates.

Another important planning consideration is the selection of the number and size of generatingunitsinstalled to achieve the desired plant capacity and energy, taking into account installed unitcosts, unitavailability, and efficiencies at various unit power outputs

HYDROELECTRIC PLANT FEATURES

The following sections willdescribe the main components such as the turbine, generator, switchgear,and generator transformer etc.

TURBINE

There are two classifications of hydraulic turbines: impulse and reaction

IMPULSE TURBINES

Used for high heads —approximately 300 m or greater High-velocity jets of water strike spoon-shaped buckets on the runner which is at atmospheric

pressure May be mounted horizontally or vertically If include perpendicular jets it is known as a Pelton type If include diagonal jets it is known as a Turgo type or cross-flow types

REACTION TURBINES

Water passes from a spiral casing through stationary radial guide vanesthrough controlgates and onto the runner blades at pressures above atmospheric

Two categories of reaction turbine —Francis and propeller Francis turbine is installed at heads up toapproximately 360 m, the water impacts the

runner blades tangentially and exits axially



Propeller turbine uses a propeller-type runner and is used at low heads —belowapproximately 45 m

Propeller runner may use fixed blades or variable pitch blades —known as a Kaplan or doubleregulated type

Water discharged from the turbine is directed into a draft tube where it exits to a tailracechannel lower reservoir, or directly to the river.

Figures are shown below



Flow Control Equipment

Flow through the turbine is controlled by wicket gates on reaction turbines and by needle nozzleson impulse turbines.

Turbine inlet valve or penstock intake gate is provided for isolation of the turbineduringshutdown and maintenance

Spillways and additional control valves and outlet tunnels are provided in the dam structure topass flows that normally cannot be routed through the turbines



Generator Two types of generators are used : Synchronous generators and induction generators Induction generators are used in small hydroelectric applications (lessthan 5 MVA) due to their

lower cost which results from elimination of the exciter, voltage regulator, andsynchronizer

associated with synchronous generators Majority of hydroelectric installations utilize salient pole synchronous generators(Salientpolemachines are used because the hydraulic turbine operates at low speeds, requiring arelatively largenumber of field poles to produce the rated frequency)

The stator consist of frame, magnetic core and windings where asrotor consist of shaft , thrustblock , spider , rim , field poles with windings , thrust bearing, upper and lower brackets for thesupport of bearings etc

WORKING: Rotor of the generator is attached with turbine with the help of a shaft.Insynchronous generator a DC current (through excitation system) is applied to the rotorwinding, which produces a rotor magnetic field. The rotor of the generator is then

turned by a prime mover(water), producing a rotating magnetic field within themachine. This rotating magnetic field induces a three phase set of voltages within thestator windings of the generator.

Fire protection systems are normally installed to detect combustion products in thegenerator

Vibration monitoring devices such as proximity probes to detect shaft runout areprovided to initiate alarms and unit shutdown

GENERATOR TERMINAL EQUIPMENT

The generator output is connected to terminal equipment via cable, busbar, or isolatedphase bus

The terminal equipment comprises current transformers (CTs), voltage transformers(VTs)(for unit protection, metering and synchronizing, and for governor and excitationsystem functions) and surge suppression devices consisting of surge arresters andcapacitors to protect the generator and low-voltage windings of the step-up transformerfrom lightning and switching-induced surge

The generator circuit breaker (may be of the oil filled, air magnetic, air blast, orcompressed gas insulated type, depending on the specific application) and associated

isolating disconnect switches are used to connect and disconnect the generator to andfrom the power system



GENERATOR STEPUP TRANSFORMER Generator output voltages range from approximately 480 VAC to 22 kVACline-to-line,

depending on the MVA rating of the unit. Generator transformer steps up the generator terminal voltage to the voltage of the

power system Generally specified and operated in accordance withinternational standards for power

transformers

EXCITATION SYSTEMS It produces DC voltage (and power) to force current to flow in the field windings of the

generator The most common arrangement is thyristor bridge others are potential source

controlled rectifier high initial response exciter ’ , bus-fed static exciter , brushlessexciter

Other Systems involving in hydropower are GOVERNOR SYSTEM ,CONTROL SYSTEM andPROTECTION SYSTEM

Special Considerations Affecting Pumped Storage Plants

A pumped storage unit is one in which the turbine and generator are operated in the reverse

direction topump water from the lower reservoir to the upper reservoir. The generator becomesa motor, drawing its energy from the power system, and supplies mechanical power to theturbine which acts as a pump The motor is started with the wicket gates closed and the drafttube water depressed with compressedair. The motor is accelerated in the pump direction andwhen at full speed and connected to the powersystem, the depression air is expelled, the pumpis primed, and the wicket gates are opened to commencepumping action.



UseFull Links ForHydroPower Studyhttp://www.builditsolar.com/Projects/Hydro/hydro.htm

http://www.alternative-energy-news.info/technology/hydro/

http://www.brighthub.com/engineering/mechanical/articles/7066.aspx

http://www.leonardo-energy.org/e-learning

http://nerg.wordpress.com/2009/02/07/n-er-g-talks-hydroelectric-power/

References Hydro electric power generation by James , Douglas Wikipedia Above mentioned links Sir LehazUllah Notes

http://www.builditsolar.com/Projects/Hydro/hydro.htm















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Hydroelectric Power Generation notes (publication by electroogle.blogspot.com)