Conventional Power Generation

Introduction

• The electric energy demand of the world is continuously increasing;

• Most of the energy is generated by conventional power plants: the only cost-effective

method for generating large quantities of energy. (economic criteria , cost effectiveness)

Fossil power plants

The first fossil power plants used steam engines as the prime mover. These plants were

evolved to an 8- to 10-MW capacity, but increasing power demands resulted in the replacement

by a more efficient steam boiler–turbine arrangement. The boilers were developed from heating

furnaces. Oil was the preferred and most widely used fuel in the beginning.

The oil shortage promoted coal-fired plants, but the adverse environmental effects

(sulfur dioxide generation, acid rain, dust pollution, etc.) curtailed their use in the late seventies.

Presently the most acceptable fuel is natural gas, which minimizes pollution and is available in

large quantities. During the next two decades, gas-fired power plants will dominate the electric

industry.

Hydro plants

Hydro energy (water falling through a head)

The hydro plants‘ ancestors are water wheels used for pumping stations, mill driving,

etc. Water-driven turbines were developed in the 20th century and used for generation of

electricity since the beginning of their commercial use.

However, most of the sites that can be developed economically are currently being utilized.

Nuclear power plants

Nuclear power plants appeared after the Second World War. The major development

occurred during the sixties(20th c); however, by the eighties environmental considerations

(10.000 years) stopped plant development in the United States and in many countries in Europe

and slowed it down all over the world.

Presently, the future of nuclear power generation is unclear, but the abundance of nuclear fuel

and the expected energy shortage and fossil plants pollution in the early part of this 21 century

may rejuvenate nuclear development if safety issues can be resolved.

Geothermal power plants

Geothermal power plants are the product of the clean energy concept, although the small-scale,

local application of geothermal energy has a long history. Presently only a few plants are in

operation.

Fossil Power Plants operational concept and major components

Fuel Handling

• The most frequently used fuels are oil, natural gas, and coal. Oil and gas are transported

by rail, on ships, or through pipelines. In the former case the gas is liquefied. Coal is

transported by rail or ships if the plant is near a river or the sea. The power plant

requires several days (coal needs weeks) of fuel reserve. Oil and gas are stored in large

metal tanks, and coal is kept in open yards. The temperature of the coal layer must be

monitored to avoid self-ignition.

• Oil is pumped and gas is fed to the burners of the boiler.

• Coal is pulverized in large mills, and the powder is mixed with air and transported by air

pressure, through pipes, to the burners. The coal transport from the yard to the mills

requires automated transporter belts, hoppers, and sometimes manually operated

bulldozers.

Boiler

Two types of boilers are used in modern power plants:

• subcritical water-tube drum-type

• supercritical once through type.

The former operates around 2500 psi, which is under the water critical pressure of

3208.2 psi. (Pounds per square inch =psi; 1 atm = 101,325 Pascals = 760 mm Hg = 760 torr =

14.7 psi.) The latter operates above that pressure, at around 3500 psi. The superheated steam

temperature is about 1000 ° F (540°C) because of turbine temperature limitations.

Typical drum-type steam boiler

Subcritical drum-type steam boiler

• A typical subcritical water-tube drum-type boiler has an inverted-U shape. On the bottom

of the rising part is the furnace where the fuel is burned. The walls of the furnace are

covered by water pipes. The drum and the superheater are at the top of the boiler. The

falling part of the U houses the reheaters, economizer (water heater), and air preheater,

which is supplied by the forced-draft fan. The induced-draft fan forces the flue gases out

of the system and sends them up the stack, which is located behind the boiler.

Fuel System

• Fuel is mixed with air and injected into the furnace

through burners. The burners are equipped with

nozzles, which are supplied by preheated air and

carefully designed to assure the optimum air-fuel

mix.

• The fuel mix is ignited by oil or gas torches.

Air-Flue Gas System

• Ambient air is driven by the forced-draft fan through the air preheater, which is heated

by the high-temperature (300 ° C) flue gases. The air is mixed with fuel in the burners

and enters into the furnace, where it supports the fuel burning. The hot combustion flue

gas generates steam and flows through the boiler to heat the superheater, reheaters,

economizer, etc. Induced-draft fans, located between the boiler and the stack, increase

the flow and send the 150 C flue gases to the atmosphere through the stack

Turbine

• The turbine converts the heat energy of the steam into mechanical energy.

• Modern power plants usually use one high-pressure and one or two lower pressure

turbines.

• High-pressure steam enters the high-pressure turbine to flow through and drive the

turbine. The exhaust is reheated in the boiler and returned to the lower-pressure units.

Both the rotor and the stationary part of the turbine have blades. The length of the

blades increases from the steam entrance to the exhaust.

Generator

The generator converts mechanical energy from the turbines into electrical energy. The

major components of the generator are the frame, stator core and winding, rotor and winding,

bearings, and cooling system. The largest machine stator is Y-connected and has two coils per

phase, connected in parallel. Most frequently, the stator is hydrogen-cooled; however, small

units may be air-cooled and very large units may be water-cooled.

Electric System

Energy generated by the power plant supplies the electric network through transmission

lines. The power plant operation requires auxiliary power to operate mills, pumps, etc. The

auxiliary power requirement is approximately 10 to 15%.

Electric System

Condenser

The condenser condenses turbine exhaust steam to water, which is pumped back to the

steam generator through various water heaters. The condensation produces a vacuum, which is

necessary to exhaust the steam from the turbine. The condenser is a shell-and-tube heat

exchanger, where steam condenses on water-cooled tubes. Cold water is obtained from the

cooling towers or other cooling systems. The condensed water is fed through a deaerator, which

removes absorbed gases from the water.

Stack and Ash Handling

• The stack is designed to disperse gases into the atmosphere without disturbing the

environment. This requires sufficient stack height, which assists the fans in removing

gases from the boiler through natural convection.

• The gases contain both solid particles and harmful chemicals. Solid particles, like dust,

are removed from the flue gas by electrostatic precipitators or bag-house filters. Harmful

sulfur dioxide is eliminated by scrubbers.

• The most common is the lime/limestone scrubbing process. Coal-fired power plants

generate a significant amount of ash. The disposition of the ash causes environmental

problems.

• Large ash particles are collected by a water- filled ash hopper, located at the bottom of

the furnace. Fly ash is removed by filters, then mixed with water.

Cooling and Feedwater System

• The condenser is cooled by cold water. The open-loop system obtains the water from a

river or sea, if the power plant location permits it. The closed-loop system utilizes cooling

towers, spray ponds, or spray canals. In the case of spray ponds or canals, the water is

pumped through nozzles, which generate fine sprays. Evaporation cools the water

sprays as they fall back into the pond. Several different types of cooling towers have

been developed. The most frequently used is the wet cooling tower, where the hot water

is sprayed on top of a latticework of horizontal bars. The water drifts downward and is

cooled, through evaporation, by the air, which is forced by fans or natural draft upward.

• The power plant loses a small fraction of the water through leakage. The feedwater

system replaces this lost water. Replacement water has to be free from absorbed

gases, chemicals, etc., because the impurities cause severe corrosion in the turbines

and boiler.

• The water treatment system purifies replacement water by pretreatment, which includes

filtering, chlorination, demineralization, condensation, polishing. These complicated

chemical processes result in a corrosion-free high-quality feedwater.

Air pollution

Air pollution is a chemical, physical (e.g. particulate matter), or biological agent that

modifies the natural characteristics of the atmosphere.

Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory

diseases.

There are many substances in the air which may impair the health of plants and animals

(including humans), or reduce visibility. These arise both from natural processes and human

activity. Substances not naturally found in the air or at greater concentrations or in different

locations from usual are referred to as 'pollutants'.

Pollutants can be classified as either primary or secondary:

Primary pollutants are substances directly produced by a process, such as ash from a volcanic

eruption or the carbon monoxide gas from a motor vehicle exhaust.

Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react

or interact.

Note that some pollutants may be both primary and secondary: that is, they are both emitted

directly and formed from other primary pollutants.

Sources of air pollution

Anthropogenic sources (human activity) related to burning different kinds of fuel

Combustion-fired power plants

Controlled burn practices used in agriculture and forestry management

• Motor vehicles generating air pollution emissions.

• Marine vessels, such as container ships or cruise ships, and related port air pollution.

• Burning wood, fireplaces, stoves, furnaces and incinerators

Other anthropogenic sources

• Oil refining, power plant operation and industrial activity in general.

• Chemicals, dust and crop waste burning in farming.

• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.

• Waste deposition in landfills, which generate methane.

• Military uses, such as nuclear weapons, toxic gases, germ warfare and rocketry.

Natural sources

• Dust from natural sources, usually large areas of land with little or no vegetation.

• Methane, emitted by the digestion of food by animals, for example cattle.

• Radon gas from radioactive decay within the Earth's crust.

• Smoke and carbon monoxide from wildfires.

• Volcanic activity, which produce sulfur, chlorine, and ash particulates.

Indoor air pollution, or Indoor air quality

• The lack of ventilation indoors concentrates air pollution where people have greatest

exposure times.

• Indoor pollution fatalities may be caused by using pesticides and other chemical sprays

indoors without proper ventilation, and many homes have been destroyed by accidental

pesticide explosions

• Carbon monoxide (CO) poisoning is a quick and silent killer, often caused by faulty vents

and chimneys, or by the burning of charcoal indoors.

• Indoors, the lack of air circulation allows these airborne pollutants to accumulate more

than they would otherwise occur in nature.

Health effects

• The World Health Organization thinks that 4.6 million people die each year from causes

directly attributable to air pollution.

• Many of these mortalities are attributable to indoor air pollution.

• Worldwide more deaths per year are linked to air pollution than to automobile accidents.

• Research published in 2005 suggests that 310,000 Europeans die from air pollution

annually.

Reduction efforts

There are many air pollution control technologies and urban planning strategies available to

reduce air pollution; however, worldwide costs of addressing the issue are high.

Many countries have programs to or are debating how to reduce dependence on fossil fuels for

energy production and shift toward renewable energy technologies or nuclear power plants.

Control devices

The following items are commonly used as pollution control devices by industry or transportation

devices. They can either destroy contaminants or remove them from an exhaust stream before

it is emitted into the atmosphere.

• Particulate control

Mechanical collectors (dust cyclones, multicyclones)

Electrostatic precipitators

Fabric filters (baghouses)

Particulate scrubbers

• NOx control

Low NOx burners

Selective catalytic reduction (SCR)

Selective non-catalytic reduction (SNCR)

NOx scrubbers

Exhaust gas recirculation

Catalytic converter (also for VOC control)

• Acid Gas/SO2 control

Wet scrubbers

Dry scrubbers

Flue gas desulfurization

• VOC abatement

Adsorption systems, such as activated carbon

Flares

Thermal oxidizers

Catalytic oxidizers

Biofilters

Absorption (scrubbing)

Cryogenic condensers

• Mercury control

Sorbent Injection Technology

Electro-Catalytic Oxidation(ECO)

K-Fuel

• Dioxin and furan control

• Ambient cleaning systems

• Associated equipment

Source capturing systems

Continuous emissions monitoring systems (CEMS)

DIRECT CURRENT GENERATOR

• Even though most common electrical appliances work fine on AC electrical power, there

are some cases when DC is preferable

• A DC generator uses electromagnetic principles to convert mechanical rotation into

electric current

• A simple DC generator consists some basic elements: a multi-turn coil rotating uniformly

in a magnetic field

• In a DC generator the two ends of the rotor coil are attached to different halves of a

single split-ring which co-rotates with the coil. The split-ring is connected to the external

circuit by means of metal/carbon brushes

• A commutator is an electrical switch that periodically reverses the current in an electrical

generator. Commutators enable generators to produce, direct current instead of

alternating current. More generally, commutators can be used to convert between direct

and alternating current.

• The purpose of the commutator is to ensure that the emf seen by the external circuit is

equal to the emf generated around the rotating coil for half the rotation period, but is

equal to minus this emf for the other half (since the connection between the external

circuit and the rotating coil is reversed by the commutator every half-period of rotation).

Terminology

The parts of an electric machine can be expressed in either mechanical terms or electrical

terms. Although distinctly separate, these two sets of terminology are frequently used

interchangeably or in combinations that include one mechanical term and one electrical term.

Mechanical

• Rotor: The rotating part of an alternator, generator or motor.

• Stator: The stationary part of an alternator, generator or motor.

Electrical

• Armature: The power-producing component of an alternator, generator or motor. The

armature can be on either the rotor or the stator.

• Field: The magnetic field component of an alternator, generator or motor. The field can

be on either the rotor or the stator and can be either an electromagnet or a permanent

magnet.

Commutation

• The placement of the (stationary) brushes guarantees that one brush always has

positive potential relative to the other. For the chosen direction of rotation, the brush with

higher potential is the one directly beneath the N-pole. (Should the rotor rotate in the

reverse direction, the opposite is true.) Thus, the brushes can serve as the terminals of

the dc source. In electric machinery, the rectifying action of the copper segments and

brushes is referred to as commutation, and the machine is called a commutating

machine.

DC machine types

The use of field winding(s) on the stator of the dc machine leads to a number of methods

to produce the magnetic field. Depending on how the field winding(s) and the rotor winding are

connected, one may have shunt excitation, series excitation, etc. Each connection yields a

different terminal characteristic. The possible connections and the resulting current–voltage

characteristics are given in the next slide.

Equivalent circuit

Equivalent circuit of generator and load.

G = generator

VG=generator open-circuit voltage

RG=generator internal resistance

VL=generator on-load voltage

RL=load resistance

DC Motors

• The relationship between mechanical rotation and electric current in an electric machine

is reversible

• A simple DC motor has a coil of wire that can rotate in a magnetic field. The current in

the coil is supplied via two brushes that make moving contact with a split ring. The coil

lies in a steady magnetic field . The forces exerted on the current-carrying wires create a

torque on the coil.

Concepts

• The generator moves an electric current, but does not create

electric charge, which is already present in the conductive wire

of its windings.

• The construction of a dynamo is similar to that of an electric

motor, and all common types of dynamos could work as

motors.

Electric Generators

Generators

• Electric generators are devices that convert energy from a mechanical form to an

electrical form. This process, known as electromechanical energy conversion,

involves magnetic fields that act as an intermediate medium.

• There are two types of generators: alternating current (ac) and direct current (dc).

Conversion

The input to the machine can be derived from a number of energy sources. For

example, in the generation of large-scale electric power, coal can produce steam that

drives the shaft of the machine. Typically, for such a thermal process, only about 1/3 of

the raw energy (i.e., from coal) is converted into mechanical energy. The final step of

the energy conversion is quite efficient(the electric generator), with an efficiency close to

100%.

Operation

• The generator‘s operation is based on Faraday‘s law of electromagnetic

induction. In brief, if a coil (or winding) is linked to a varying magnetic field, then

an electromotive force, or voltage, emf, is induced across the coil (movie).

• Thus, generators have two essential parts: one creates a magnetic field, and the

other where the emf ‘s are induced.

Components

• The magnetic field is typically generated by electromagnets (thus, the field

intensity can be adjusted for control purposes), whose windings are referred to

as field windings or field circuits

• The coils where the emf‘s are induced are called armature windings or armature

circuits

• One of these two components is stationary (stator), and the other is a rotational

part (rotor) driven by an external torque.

• Conceptually, it is immaterial which of the two components is to rotate because,

in either case, the armature circuits always ―see‖ a varying magnetic field.

• However, practical considerations lead to the common design that for ac

generators, the field windings are mounted on the rotor and the armature

windings on the stator. In contrast, for dc generators, the field windings are on

the stator and armature on the rotor.

AC Generators

• Today, most electric power is produced by synchronous generators.

Synchronous generators rotate at a constant speed, called synchronous

speed . This speed is dictated by the operating frequency of the system and the

machine structure.

• There are also ac generators that do not necessarily rotate at a fixed speed such

as those found in windmills (induction generators); these generators, however,

account for still a small percentage of today‘s

generated power.

Synchronous Generators

- uses a rotating magnetic field

- magnet in the centre will rotate at a constant speed which

is synchronous with the rotation of the magnetic field

• The rotor consists of a winding wrapped around a steel body. A dc current is

made o flow in the rotor winding (or field winding), and this results in a magnetic

field (rotor field).

• When the rotor is made to rotate at a constant speed, the three stationary

windings aa ′ , bb’, and cc’ experience a periodically varying magnetic field. Thus,

emf‘s are induced across these windings in accordance with Faraday‘s law.

These emf ‘s are ac and periodic;

• each period corresponds to one revolution of the rotor. Thus, for 50-Hz electricity,

the rotor has to rotate at 3000 revolutions per minute (rpm); this is the

synchronous speed of the given machine.

emf waveforms

Because the windings aa′,bb′, and cc′ are displaced equally in space from each

other (by 120 degrees), their emf waveforms are displaced in time by 1/3 of a period.

Voltage Variation for Three Phase Alternating Current

A full cycle lasts 20 milliseconds (ms) in a 50 Hz grid. Each of the three phases

then lag behind the previous one by 20/3 = 6 2/3 ms

machine with p poles

• It is possible to build a machine with p poles, where p= 4, 6, 8, . . . (even

numbers). For example, the crosssectional view of a four-pole machine is given

in the next slide.

Four Pole Synchronous Generator

• The rotors depicted in Figs. are salient since the

poles are protruding from the shaft. Such structures

are mechanically weak, since at a high speed

(3000 rpm and 1500 rpm, respectively) the

centrifugal force becomes a serious problem.

Practically, for high-speed turbines, round-rotor (or

cylindrical-rotor) structures are preferred.

Windings 3 Phase Connection

Mathematical/Circuit Models.

• There are various models for synchronous machines, depending on how much

detail one needs in an analysis.

• In the simplest model, the machine is equivalent to a constant voltage source in

series with an impedance.

• In more complex models, numerous nonlinear differential equations are involved.

mathematical model

• The mathematical model for round-rotor machines is much simpler than that for

salient-rotor ones. This stems from the fact that the rotor body has a permeability

much higher than that of the air.

auxiliary devices

• In addition to the basic components of a synchronous generator (rotor, stator,

and their windings), there are auxiliary devices which help maintain the

machine‘s operation within acceptable limits.

• Three such devices are mentioned here: governor, damper windings, and

excitation control system.

Governor

• This is to control the mechanical power input Pin. The control is via a feedback

loop where the speed of the rotor is constantly monitored.

• For instance, if this speed falls behind the synchronous speed, the input is

insufficient and has to be increased. This is done by opening up the valve to

increase the steam for turbogenerators or the flow of water through the penstock

for hydrogenerators. Governors are mechanical systems and therefore have

some significant time lags (many seconds) compared to other

electromagnetic phenomena associated with the machine.

Damper windings (armortisseur windings).

• These are special conducting bars buried in notches on the rotor surface, and the

rotor resembles that of a squirrel-cage-rotor induction machine.

• The damper windings provide an additional stabilizing force for the machine

when it is perturbed from an equilibrium. As long as the machine is in a steady

state, the stator field rotates at the same speed as the rotor, and no currents are

induced in the damper windings. That is, these windings exhibit no effect on a

steady-state machine. However, when the speeds of the stator field and the rotor

become different (because of a disturbance), currents are induced in the damper

windings in such a way as to keep, according to Lenz‘s law, the two speeds from

separating.

Excitation control system

• Modern excitation systems are very fast and quite efficient. An excitation control

system is a feedback loop that aims at keeping the voltage at machine terminals

at a set level. Assume that a disturbance occurs in the system, and as a result,

the machine‘s terminal voltage Vt drops. The excitation system boosts the

internal voltage EF ; this action can increase the voltage Vt and also tends to

increase the reactive power output.

• From a system viewpoint, the two controllers of excitation and governor rely on

local information (machine‘s terminal voltage and rotor speed).

Superconducting Generators

• The demand for electricity has increased steadily over the years. To satisfy the

increasing demand, there has been a trend in the development of generators

with very high power rating. This has been achieved, to a great extent, by

improvement in materials and cooling techniques. Cooling is necessary because

the loss dissipated as heat poses a serious problem for winding insulation.

• The progress in machine design based on conventional methods appears to

reach a point where further increases in power ratings are becoming difficult. An

alternative method involves the use of superconductivity.

• In a superconducting generator, the field winding is kept at a very low

temperature so that it stays superconductive.

• An obvious advantage to this is that no resistive loss can take place in this

winding, and therefore a very large current can flow. A large field current yields a

very strong magnetic field, and this means that many issues considered

important in the conventional design may no longer be critical.

• the conventional design makes use of iron core for armature windings to achieve

an appropriate level of magnetic flux for these windings;

• iron cores, however, contribute to heat loss—because of the effects of hysteresis

and eddy currents— and therefore require appropriate designs for winding

insulation. With the new design, there is no need for iron cores since the

magnetic field can be made very strong; the absence of iron allows a simpler

winding insulation, thereby accommodating additional armature windings.

critical field strength

• There is, however, a limit to the field current increase. Increasing the current

produces more and more magnetic lines of force, and this can continue until the

dense magnetic field can penetrate the material.

• When this happens, the material fails to stay superconductive,and therefore

resistive loss can take place. In other words, a material can stay superconductive

until a certain critical field strength is reached.

efficiency of generators

It is expected that the use of superconductivity adds another 0.4% to the

efficiency of generators. This improvement might seem insignificant (compared to an

already achieved figure of 98% by the conventional design) but proves considerable in

the long run.

It is estimated that given a frame size and weight, a superconducting generator‘s

capacity is three times that of a conventional one.

Induction Generators

Conceptually, a three-phase induction machine is similar to a synchronous

machine, but the former has a much simpler rotor circuit.

The stator is identical.

A typical design of the rotor is the squirrel-cage structure, where conducting bars

are embedded in the rotor body and shorted out at the ends.

Asynchronous (Induction) Generators

- the rotor is provided with an "iron" core, using a stack of thin insulated steel

laminations, with holes punched for the conducting aluminium bars

- adapts itself to the number of poles in the stator automatically

- the rotor is placed in the middle of the stator, which in this case, is a 4-pole stator

which is directly connected to the three phases of the electrical grid

motor

• When a set of three-phase currents (waveforms of equal amplitude, displaced in

time by one-third of a period) is applied to the stator winding, a rotating magnetic

field is produced. Currents are therefore induced in the bars, and their resulting

magnetic field interacts with the stator field to make the rotor rotate in the same

direction.

• In this case, the machine acts as a motor since, in order for the rotor to rotate,

energy is drawn from the electric power source. When the machine acts as a

motor, its rotor can never achieve the same speed as the rotating field (this is the

synchronous speed) for that would imply no induced currents in the rotor bars.

Motor Operation

- we have a magnetic field which moves relative to the rotor which induces a very

strong current in the rotor bars which offer very little resistance to the current,

since they are short circuited by the end rings

- the rotor then develops its own magnetic poles, which in turn become dragged along

by the electromagnetic force from the rotating magnetic field in the stator

Compensation

• It is ideal to have a compensation in which the capacitor and equivalent inductor

completely cancel the effect of each other. In windmill applications, for example,

this faces a great challenge because the varying speed of the rotor (as a result of

wind speed) implies a varying equivalent inductor.

• Fortunately, strategies for ideal compensation have been designed and put to

commercial use.

Generator

• If an external mechanical torque is applied to the rotor to drive it beyond the

synchronous speed, however, then electric energy is pumped to the power grid,

and the machine will act as a generator.

• An advantage of induction generators is their simplicity (no separate field circuit)

and flexibility in speed.

• These features make induction machines attractive for applications such as

windmills.

• A disadvantage of induction generators is that they are highly inductive. Because

the current and voltage have very large phase shifts, delivering a moderate

amount of power requires an unnecessarily high current on the power line. This

current can be reduced by connecting capacitors at the terminals of the machine.

Capacitors have negative reactance; thus, the machine‘s inductive reactance can

be compensated.

Energy Transmission and Distribution

Purpose

The purpose of the electric transmission system is the interconnection of the

electric energy producing power plants or generating stations with the loads.

Three-phase AC system

• A three-phase AC system is used for most transmission lines .

• The three-phase system has three phase conductors. The system voltage is

defined as the rms voltage between the conductors, also called line-to-line

voltage. The voltage between the phase conductor and ground, called line-to-

ground voltage, is equal to the line-to-line voltage divided by the square root of

three .

• The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia,

and part of Asia.

Fig.1 The concept of typical energy transmission and distribution systems

The generator voltage

The generating station produces the electric energy. The generator voltage is

around 5 to 6 kV. This relatively low voltage is not appropriate for the transmission of

energy over long distances. The energy is supplied through step-up transformers to the

electric network. To reduce energy transportation losses, step-up transformers increase

the voltage and reduce the current.

Transformer

At the generating station a transformer is used to increase the voltage and reduce the

current. In Fig. 1 the voltage is increased to 400 kV and an extra-high-voltage (EHV)

line transmits the generator-produced energy to a distant substation. Such substations

are located on the outskirts of large cities or in the center of several large loads.

The high-voltage network

• The high-voltage network, consisting of transmission lines, connects the power

plants and high-voltage substations in parallel.

• This network permits load sharing among power plants and assures a high level

of reliability. The failure of a line or power plant will not interrupt the energy

supply.

Efficiency

• 600A*1Ω => 360 kW

• 138 kV transmits 83 MW with η= 99.57%

• 14 kV transmits 8.3 MW with η= 95.65%

Corona, reactance

• High voltage => high electric field gradients

• Electric discharge sounds like a buzz

• Reactance asks for capacitors

High-voltage substations

• The voltage is reduced at the 400 kV/220 kV EHV substation to the high-voltage

level and high-voltage lines transmit the energy to high-voltage substations

located within cities.

• At the high-voltage substation the voltage is reduced to 110 kV.

Distribution substations

• Sub-transmission lines connect the high-voltage substation to many local

distribution stations located within cities. Sub-transmission lines

are frequently located along major streets.

• The voltage is reduced to 12 or 20 kV at the distribution substation. Several

distribution lines emanate from each distribution substation as overhead or

underground lines.

Distribution lines, distribution transformer

• Distribution lines distribute the energy along streets and alleys. Each line

supplies several step-down transformers distributed along the line. The

distribution transformer reduces the voltage to 400/230 V, which supplies

houses, shopping centers, and other local loads. The large industrial plants and

factories are supplied directly by a subtransmission line or a dedicated

distribution line.

Overhead and underground transmission

• The overhead transmission lines are used in open areas such as

interconnections between cities or along wide roads within the city. In congested

areas within cities, underground cables are used for electric energy transmission.

The underground transmission system is environmentally preferable but has a

significantly higher cost. In Fig. 1 the 12-kV line is connected to a 12-kV cable

which supplies commercial or industrial customers. The figure also shows 12-kV

cable networks supplying downtown areas in a large city. Most newly developed

residential areas are supplied by 12-kV cables through pad-mounted step-down

transformers as shown in Fig.1

Subtransmission system

• In high load density areas, the subtransmission system uses a network

configuration that is similar to the highvoltage network.

• In medium and low load density areas, the loop or radial connection is used. The

above Figure 2 shows a typical radial connection.

The distribution system

• The distribution system has two parts, primary and secondary.

• The primary distribution system consists of overhead lines or underground

cables, which are called feeders. The feeders run along the streets and supply

the distribution transformers that step the voltage down to the secondary level

(230–400 V).

• The secondary distribution system contains overhead lines or underground

cables supplying the consumers directly (houses, light industry, shops, etc.) by

single- or three-phase power.

Dedicated primary feeders

• Separate, dedicated primary feeders supply industrial customers requiring

several megawatts of power.

• The subtransmission system directly supplies large factories consuming over 50

MW.

Capacitor bank

A three-phase switched capacitor bank is rated two-thirds of the total average

reactive load and installed two-thirds of the distance out on the feeder from the source.

The capacitor bank improves the power factor and reduces voltage drop at heavy loads.

However, at light loads, the capacitor is switched off to avoid overvoltages.

Voltage regulation

Some utilities use voltage regulators at the primary feeders. The voltage

regulator is an autotransformer. The secondary coil of the transformer has 32 taps, and

a switch connects the selected tap to the line to regulate the voltage. The problem with

the tap changer is that the lifetime of the switch is limited. This permits only a few

operations per day.

3-ph and 1-ph

• A three-phase line supplies the larger loads. These loads are protected by CBs

or high-power fuses.

• The lateral single-phase feeders are supplied from different phases to assure

equal phase loading.

• Fuse cutouts protect the lateral feeders. These fuses are coordinated with the

fuses protecting the distribution transformers.

• The fault in the distribution transformer melts the transformer fuse first. The

lateral feeder fault operates the cutout fuse before the recloser or CB opens

permanently.

Rural areas

• Most primary feeders in rural areas are overhead lines using pole-mounted

distribution transformers. The capacitor banks and the reclosing and

sectionalizing switches are also pole-mounted. Overhead lines reduce the

installation costs but reduce aesthetics.

Urban areas

• In urban areas, an underground cable system is used. The switchgear and

transformers are placed in underground vaults or ground-level cabinets. The

underground system is not affected by weather and is highly reliable.

• The high cost limits the underground system to high-density urban areas and

housing developments.

Geothermal Power Plants

The source of geothermal energy.

• The solid crust of the earth is an average of 32 km deep. Under the solid crust is

the molten mass, the magma.

• The heat stored in the magma is the source of geothermal energy.

• The hot molten magma comes close to the surface at certain points in the earth

and produces volcanoes, hot springs, and geysers.

Hydrothermal Source

• This is the most developed source. Power plants, up to a capacity of 2000 MW,

are in operation worldwide.

• Heat from the magma is conducted upward by the rocks. The groundwater drifts

down through the cracks and fissures to form reservoirs when water-

impermeable solid rock bed is present. The water in this reservoir is heated by

the heat from the magma.

• Depending on the distance from the magma and rock configuration, steam, hot

pressurized water, or the mixture of the two are generated.

• The reservoir is tapped by a well, which brings the steam-water mixture to the

surface to produce energy.

The geothermal power plant concept

• The hot water and steam mixture is fed into a separator. If the steam content is

high, a centrifugal separator is used to remove the water and other particles. The

obtained steam drives a turbine. The typical pressure is around 100* psi and the

temperature is around 200 ° C .

• The water is returned to the ground, the steam drives the turbine. Typically the

steam entering the turbine has a temperature of 120 to 150 °C and a pressure of

30 to 40 psi.

• The turbine drives a conventional generator. The typical rating is in the 20- to

100-MW range.

Concept of a geothermal power plant

problems with geothermal power

• Major problems with geothermal power plants are the minerals and

noncondensable gases in the water. The minerals make the water highly

corrosive, and the separated gases cause air pollution.

• An additional problem is noise pollution. The centrifugal separator and

blowdowns require noise dampers and silencers.

Measuring units conversion

• Pounds per square inch (psi, PSI, lb/in2, lb/sq in)

Commonly used in the U.S., but not elsewhere. Normal atmospheric pressure is

14.7 psi, which means that a column of air one square inch in area rising from the

Earth's atmosphere to space weighs 14.7 pounds

• Atmosphere (atm) Normal atmospheric pressure is defined as 1 atmosphere. 1

atm = 14.6956 psi = 760 torr

• Pascal (Pa) 1 pascal = a force of 1 Newton per square meter (1 Newton = the

force required to accelerate 1 kilogram one meter per second per second = 1

kg.m/s2; this is actually quite logical for physicists and engineers, honest). 1

pascal = 10 dyne/cm2 = 0.01 mbar.

• 1 atm = 101,325 Pascals = 760 mm Hg = 760 torr = 14.7 psi.

Hydroelectric Power Plants

Hydroelectric power plant

• Hydroelectric power plants convert energy produced by a water head into electric

energy.

• The head is produced by building a dam across a river, which forms the upper-

level reservoir.

• In the case of low head, the water forming the reservoir is fed to the turbine

through the intake channel or the turbine is integrated in the dam.

• The water in the reservoir is considered stored energy. When the gates open, the

water flowing through the penstock becomes kinetic energy because it's in

motion.

• The water strikes and turns the large blades of a turbine, which is attached to a

generator above it by way of a shaft .

• The generator converts the mechanical energy of the turbine in electric energy.

typical hydroelectric power plant arrangement

High-Head Plants.

High-head plants are built with impulse turbines, where the head-generated

water pressure is converted into velocity by nozzles and the high-velocity water jets

drive the turbine runner.

Low- and Medium-Head Plants

• Low- and medium-head installations are built with reaction-type turbines, where

the water pressure is mostly converted to velocity in the turbine.

The two basic classes of reaction turbines are:

• the propeller or Kaplan type, mostly used for low-head plants,

• the Francis type, mostly used for medium-head plants.

low-head Kaplan turbine

• The cross section of a typical low-head

Kaplan turbine is shown below.

• The vertical shaft turbine and generator are

supported by a thrust bearing immersed in

oil. The generator is in the upper, watertight

chamber.

• The turbine runner has 4 to 10 propeller

types, and adjustable pitch blades.The

blades are regulated from 5 to 35 degrees by an oil-pressure-operated servo

mechanism.

• The water is evenly distributed along the periphery of the runner by a concrete

spiral case and regulated by adjustable wicket blades.

• The water is discharged from the turbine through an elbow-shaped draft tube.

The conical profile of the tube reduces the water speed from the discharge speed

of 3–10 m/s to 0.4 m/s to increase turbine efficiency.

Francis Turbine

• The most common type of turbine for hydropower plants is the Francis Turbine,

which looks like a big disc with curved blades. A turbine can weigh as much as

172 tons and turn at a rate of 90 revolutions per minute (rpm).

Electric equipment

• Transformer - The transformer inside the powerhouse takes the AC and

converts it to higher-voltage current.

• Power lines - Out of every power plant come four wires: the three phases of

power being produced simultaneously plus a neutral or ground common to all

three.

• Outflow - Used water is carried through pipelines, called tailraces, and re-enters

the river downstream.

SMALL AND MICRO HYDRO POWER PLANTS

sustainable development concept is concerning the present and future

development at worldwide level through co – generative, clean and renewable

energy sources. This new and modern concept asks to develop new researches

and scientific developments suitable for different applications, such as:

• large – scale applications of renewable energy in transmission and distribution

systems,

• large – scale applications of renewable energy in autonomous and weakly

connected systems

Introduction RO

• Governmental financed researches are estimating the technical realistic

potential at 1100 MW, with a possible production from 2 TWh/y to 3.76 TWh/y .

This potential had attracted the interest long time before. There were planed,

during the socialist economy, in the ‘80-th to built till ‗ 95 a number of 538 MHP

covering a total power of 420 MW. At the end of ‘88 were in different stages of

construction 115 MHP but only 53 are finally working.

• Micropotentialul amenajat la 31.12.2005 totalizeaza 380 de microhidrocentrale cu

puterea instalata de 502 MW si energia medie de proiect 1153 GWh/an.

• Din totalul de microhidrocentrale existente in Romania:

• 71% sunt in exploatare;

• 13% sunt in executie;

• 9% care nu functioneaza;

• 7% sunt vandute.

• Din total de 502 MW putere instalata in microhidrocentralele existente:

• 66% sunt instalati in MHC aflate in exploatare la Hidroelectrica;

• 25% sunt instalati in MHC aflate in executie;

• 2% sunt instalati in MHC care nu functioneaza;

• 7% sunt instalati in MHC privatizate.

History

From the Historical point of view, the use of hydro power is coming from

ancient ages in Romania. Very interesting technical solutions were designed by

ingenious Romanian Magister Naturalis . What is known as a Pelton-Turgo

turbine was invented many centuries before by such ingenious Romanian

Magister Naturalis.

Moara cu facaie

• ―The turbine is made by wood .The horizontal turbine consists in wood carved

Wing spoons.

• The pipe for the water adduction ( jgheab) is made by wood, too, with different

sections acting like the nowadays nozzle.

• The water is oriented by the jgheab into the carved part of the facaie , ensuring a

maximum transformation of the total water energy into the kinetic energy.

The objective

The objective of a hydro power scheme is to convert the potential

energy of a mass of water, flowing in a stream with a certain fall (termed the

―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.

Hydroelectric generating plants come in many sizes--from huge plants that

produce more electricity than most countries can use, to very small plants that

supply electricity for a single house.

-The "small-scale hydro" or "small hydro‖ supply electric power under the range

from 1 to 5 MW.

-Hydroelectric plants which supply electric power in the range from about 1000

kilowatts to 100 kilowatts are called mini-hydroelectric or mini-hydro.

-Hydroelectric plants which supply electric power under 100 (50) kilowatts are

called micro-hydroelectric or micro-hydro.

According to the head, schemes can be classified in three categories:

• High head: 100-m and above

• Medium head: 30 - 100 m

• Low head: 2 - 30 m

Schemes can also be defined as:

• Run-of-river schemes

• Schemes with the powerhouse located at the base of a dam

• Schemes integrated on an canal or in a water supply pipe

run-of-river

In the ―run-of-river‖ schemes the turbine generates electricity as and when the

water is available and provided by the river.

When the river dries up and the flow falls below some predetermined amount -

the minimum technical flow of the turbine equipping the plant -, generation ceases :

Hydroelectric generating plants come in many -site dependent solutions

• Medium and high head schemes use weirs to divert water to the intake, from

where it is conveyed to the turbines, via a pressure pipe or penstock. Penstocks

are expensive and consequently this design is usually uneconomic.

• An alternative is to convey the water by a low-slope canal, running alongside the

river, to the pressure intake or forebay, and then in a short penstock to the

turbines.

• If the topography and morphology of the terrain does not permit the easy layout

of a canal, a low-pressure pipe, with larger latitude in slopes, can be an

economical option.

site dependent solutions

• Occasionally a small reservoir, storing enough water to operate only on peak

hours, when ―buy-back‖ rates are higher, can be created by the weir, or a

similarly sized pond can be built in the forebay, using the possibilities provided by

geotextiles.

TurbinaGenerator

Conducta

fortata

Conducta

evacuare

Aductiune

Bazin de acumulare

Cladirea

Centralei

Spre consumatori

Curs de

apa

• At the outlet of the turbines, the water is discharged to the river, via the tailrace

Low head schemes are typically built in river valleys.

Two technological options can be selected:

• the water is diverted to a power intake with a short penstock, as in the high head

schemes-A

• the head is created by a small dam, provided with sector gates and an integrated

intake, powerhouse and fish ladder-B

About Hydraulic Engineering

Water flow in pipes, channels

Water flow in pipes: Bernoulli‘s equation

• The total energy at point 1 is then the algebraic sum of the potential energy, the

pressure energy , and the kinetic energy.

• Where H1 is the total energy, h1 is the elevation head, P1 the pressure, gama

the specific weight of water, V1 the velocity of the water and g the gravitational

acceleration.

laminar flow

• The water flows in laminae, like concentric thin walled concentric pipes.

• If water is allowed to flow very slowly in a long, straight, glass pipe of small bore

into which a fine stream of coloured water is introduced at the entrance to the

pipe, the coloured water appeared as a straight line all along the pipe, indicating

laminar flow.

concentric thin walled concentric pipes

• The outer virtual pipe adheres to the wall of the real pipe, while each of the inner

ones moves at a slightly higher speed, which reaches a maximum value near the

centre of the pipe.

• The velocity distribution has the form of a paraboloid of revolution and the

average velocity

is 50% of the maximum centre line velocity.

turbulent flow

If the flow rate is gradually increased, a moment is reached when the thread of

colour suddenly breaks up and mixes with the surrounding water. The particles close to

the wall mix up with the ones in the midstream, moving at a higher speed, and slow

them. At that moment the flow becomes turbulent, and the velocity distribution curve is

much flatter.

Water loses energy as it flows through a pipe, fundamentally due to:

1. friction against the pipe wall

2. viscous dissipation as a consequence of the internal friction of flow.

The friction against the pipe wall depends on the wall material roughness and the

velocity gradient nearby the wall. Velocity gradient, as can be seen in figure above, is

higher in turbulent flow than in laminar flow.

for water flowing between two sections, a certain

amount of energy hf is lost

Empirical formulae

Over the years many empirical formulae, based on accumulated experience, have been

developed. They are, in general, not based on sound physical principles and even,

occasionally, lack dimensional coherence, but are intuitively based on the belief that the

friction on a closed full pipe is:

1. Independent of the water pressure

2. Linearly proportional to its length

3. Inversely proportional to a certain power of its diameter

4. Proportional to a certain exponent of the water velocity

5. In turbulent flows it is influenced by the wall roughness

Loss of head in bends

• Pipe flow in a bend, experiences an increase of pressure along the outer wall

and a decrease of pressure along the inner wall. This pressure unbalance

causes a secondary current such as shown in the figure 2.11. Both movements

together - the longitudinal flow and the secondary current - produces a spiral flow

that, at a length of around 100 diameters, is dissipated by viscous friction.

• The head loss produced in these circumstances depends on the radius of the

bend and on the diameter of the pipe. Furthermore, in view of the secondary

circulation, there is a secondary friction loss, dependent of the relative roughness

e/d.

• There is also a general agreement that, in seamless steel pipes, the loss in

bends with angles under 90º, is almost proportional to the bend angle.

Loss of head through valves

Valves or gates are used in small hydro scheme to isolate a component from the rest,

so they are either entirely closed or entirely open. Flow regulation is assigned to the

distributor vanes or to the needle valves of the turbine.

The loss of head produced by the water flowing through an open valve depends on the

type and manufacture of the valve.

Water flow in open channels

Any kind of canal, even a straight one, has a three-dimensional distribution of velocities.

A well-established principle in fluid mechanics is that any particle in contact with a solid

stationary border has a zero velocity. Figure 2.14 illustrates the iso-velocity lines in

channels of different profile. The mathematical approach is based on the theory of the

boundary layer; the engineering approach is to deal with the average velocity V.

Powerhouse

• In a small hydropower scheme the role of the powerhouse is to protect from the

weather hardships the electromechanical equipment that convert the potential

energy of water into electricity.

• The number, type and power of the turbo-generators, their configuration, the

scheme head and the geomorphology of the site controls the shape and size of

the building.

Hydraulic Turbines

• The purpose of a hydraulic turbine is to transform the water potential energy to

mechanical rotational energy.

• The potential energy in the water is converted into mechanical energy in the

turbine, by one of two fundamental and basically different mechanisms:

• - The water pressure can apply a force on the face of the runner blades, which

decreases as it proceeds through the turbine. Turbines that operate in this way

are called reaction turbines. The turbine casing, with the runner fully immersed

in water, must be strong enough to withstand the operating pressure.

• - The water pressure is converted into kinetic energy before entering the runner.

The kinetic energy is in the form of a high-speed jet that strikes the buckets,

mounted on the periphery of the runner. Turbines that operate in this way are

called impulse turbines. As the water after striking the buckets falls into the tail

water with little remaining energy, the casing can be light and serves the purpose

of preventing splashing.

Impulse turbines: Pelton turbines

Pelton turbines are impulse turbines where one or more jets impinge on a wheel

carrying on its periphery a large number of buckets. Each jet issues through a nozzle

with a needle (or spear) valve to control the flow .

They are only used for relatively high heads.

Impulse turbines: Pelton turbines

Impulse turbines: Turgo turbines

• The Turgo turbine can operate under a head in the range of 30-300 m. Like the

Pelton it is an impulse turbine, but its buckets are shaped differently and the jet of

water strikes the plane of its runner at an angle of 20º.

Comparison: Pelton vs Turgo

Whereas the volume of water a Pelton turbine can admit is limited because the

water leaving each bucket interferes with the adjacent ones, the Turgo runner does not

present this problem. The resulting higher runner speed of the Turgo makes direct

coupling of turbine and generator more likely, improving its overall efficiency and

decreasing maintenance cost.

Impulse turbines: Banki-Michell = Cross-flow turbines

Banki-Michell turbines can operate with discharges between 20 litres/sec and

10 m3/sec and heads between 1 and 200 m.

Water enters the turbine, directed by one or more guide-vanes located in a transition

piece upstream of the runner, and through the first stage of the runner which runs full

with a small degree of reaction. Flow leaving the first stage attempt to crosses the open

centre of the turbine. As the flow enters the second stage, a compromise direction is

achieved which causes significant shock losses.

The runner is built from two or more parallel disks connected near their rims by a series

of curved blades).

Their efficiency lower than conventional turbines, but remains at practically the same

level for a wide range of flows and heads (typically about 80%).

Reaction turbines

The water pressure can apply a force on the face of the runner blades, which

decreases as it proceeds through the turbine = Reaction turbines:

• Francis turbines

• Kaplan

• propeller turbines

Francis turbines.

• Francis turbines are radial flow reaction turbines, with fixed runner blades and

adjustable guide vanes, used for medium heads.

• In the high speed Francis the admission is always radial but the outlet is axial.

• The water proceeds through the turbine as if it was enclosed in a closed conduit

pipe, moving from a fixed component, the distributor, to a moving one, the

runner, without being at any time in contact with the atmosphere.

Kaplan and propeller turbines

• Kaplan and propeller turbines are axial-flow reaction turbines, generally used for

low heads. The Kaplan turbine has adjustable runner blades and may or may not

have adjustable guide- vanes If both blades

and guide-vanes are adjustable it is

described as ―double-regulated‖. If the

guide-vanes are fixed it is ―single-regulated‖.

• Unregulated propeller turbines are used

when both flow and head remain practically

constant

• The double-regulated Kaplan, illustrated in

figure below is a vertical axis machine with a

scroll case and a radial wicket-gate

configuration

propeller turbines ;Bulb units

Bulb units are derived from Kaplan turbines, with the generator contained in a

waterproofed bulb submerged in the flow..

Pumps working as turbines

Standard centrifugal pumps may be operated as turbines by directing flow

through them from pump outlet to inlet. Since they have no flow regulation they can

operate only under relatively constant head and discharge.

Pumps working as turbines

Standard centrifugal pumps

may be operated as turbines by

directing flow through them from

pump outlet to inlet. Since they

have no flow regulation they can

operate only under relatively

constant head and discharge.

Small and Micro HPP: Electromechanical Components and their Control

Speed increasers

• When the turbine and the generator operate at the same speed and can be

placed so that their shafts are in line, direct coupling is the right solution; virtually

no power losses are incurred and maintenance is minimal.

• In many instances, particularly in the lowest power range, turbines run at less

than 400 rpm, requiring a speed increaser to meet the 1 000-1 500 rpm of

standard alternators. Turbine manufactures will recommend the type of coupling

to be used, either rigid or flexible although a flexible coupling that can tolerate

certain misalignment is usually recommended. In the range of powers

contemplated in small hydro schemes this solution is always more economical

than the use of a custom made alternator.

Generators

Generators transform mechanical energy into electrical energy.

Nowadays only three-phase alternating current generators are used in normal practice.

Depending on the characteristics of the network supplied, the producer can choose

between:

- Synchronous generators

- Asynchronous generators.

Asynchronous generators

IG are simple squirrel-cage induction motors with no possibility of voltage regulation

and running at a speed directly related to system frequency.

They draw their excitation current from the grid, absorbing reactive energy by

their own magnetism.

Adding a bank of capacitors can compensate for the absorbed reactive energy.

IG cannot generate when disconnected from the grid because are incapable of

providing their own excitation current (without an external source of reactive energy).

Synchronous generators

• SG are equipped with a DC excitation system (rotating or static) associated with

a voltage regulator, to provide voltage, frequency and phase angle control before

the generator is connected to the grid;

• SG supply the reactive energy required by the power system when the generator

is tied into the grid.

• Synchronous generators can run isolated from the grid and produce power since

excitation is not grid-dependent.

• Synchronous generators are more expensive than asynchronous generators and

are used in power systems where the output of the generator represents a

substantial proportion of the power system load.

• Asynchronous generators are cheaper and are used in large grids where their

output is an insignificant proportion of the power system load. Their efficiency is 2

to 4 per cent lower than the efficiency of synchronous generators over the entire

operating range.

• In general, when the power exceeds 5000 kVA a synchronous generator is

installed.

working voltage of the generator

• The working voltage of the generator varies with its power.

• The standard generation voltages are:

• 430 V up to 1400 kVA

• 6000/6600 V for bigger installed power.

• Generation at 430 V allows the use of standard distributor transformers as outlet

transformers and the use of the generated current to feed into the plant power

system.

• Generating at medium voltage requires an independent transformer MT/LT to

supply the plant services.

VSG relying on Power Electronics

• Recently, variable-speed constant-frequency systems (VSG), relying on Power

Electronics, in which turbine speed is permitted to fluctuate widely, while the

voltage and frequency are kept constant and undistorted, have entered the

market.

• This system can even ―synchronise‖ the unit to the grid before it starts rotating.

• The key to the system is the use of a electronic converter in conjunction with a

IG.

• Unfortunately its cost price is still rather high (but see Wind Generators).

Generator configurations

• Generators can be manufactured with horizontal or vertical axis, independently of

the turbine configuration. E.G.:A vertical axis Kaplan turbine turning at 214 rpm is

directly coupled to a custom made 28 poles alternator.

• A flywheel is frequently used to smooth-out speed variations and assists the

turbine control.

• When the generators are small, they have an open cooling system, but for larger

units it is recommended to use a closed cooling circuit provided with air-water

heat exchangers.

synchronisation

• The mains supply defines the frequency of the stator rotating flux and hence the

synchronous speed above which the rotor shaft must be driven.

• On start-up, the turbine is accelerated up to 90-95% of the synchronous speed of

the generator, when a velocity relay close the main line switch. The SG passes

immediately to hyper-synchronism and the driving and resisting torque are

balanced in the area of stable operation.

• The IG case the turbine is accelerated up to 105% of the synchronous speed and

the driving and resisting torque are balanced in the area of stable operation at

the mains frequency.

SG Voltage regulation

Exciters for synchronous generator:

The exciting current for the synchronous generator can be supplied by a small DC

generator, known as the exciter, to be driven from the main shaft.

The power absorbed by this dc generator amounts to 0.5% - 1.0% of the total generator

power.

Nowadays a static exciter usually replaces the DC generator, but there are still many

rotating exciters in operation.

Voltage regulation: Asynchronous generators

• An asynchronous generator needs to absorb a certain power from the three-

phase mains supply to ensure its magnetisation.

• The IG can receive its reactive power from a separate source such as a bank of

capacitors.

• Due to cost issues, a lot of effort was made over the years to improve the IG

control for making it suitable to equip stand-alone MHPs.

• Recent advances in Power Electronics and μP technologies are offering the

possibility to favorably solve the IG control problem.

• When the load changes, control is necessary to maintain the produced electric

energy in an acceptable range.

• A variable load is affecting mainly two electric energy parameters: the voltage

and the frequency.

Turbine control

Turbines are designed for a certain net head and discharge. Any deviation from these

parameters must be compensated for, by opening or closing control devices such as the

wicket-vanes or gate valves to keep constant, either the outlet power, the level of the

water surface in the intake or the turbine discharge.

In schemes connected to an isolated net, the parameter to be controlled is the runner

speed, which control the frequency. The generator becomes overloaded and the turbine

slows-down. In this case there are basically two approaches to control the runner

speed:

• by controlling the water flow to the turbine;

• keeping the water flow constant and adjusting the electric load by an electric

ballast load connected to the generator terminals.

Stand alone SHP and MHP

Variable load is affecting two electric parameters: the voltage and the frequency.

• The voltage can be controlled through the excitation current by means of the

excitation circuit. The excitation current is flowing through highly inductive

circuits; consequently, the circulated power is the reactive power.

• The frequency is basically related to the active power of the load circuit.

• The dependence between the induced EMF and frequency is affected by the

nonlinear characteristic of the magnetic circuit. The interdependence between

the two parameters control has also to be considered.

IG Voltage control

• The voltage control is requiring a reactive power balance in the network.

• The performance of the IG voltage control circuit is highly influenced by the

structure of the excitation circuit.

• In simple terms the voltage is regulated by the means of the self exciting

capacitors in such cases. By controlling the reactive power, VAR, through the

capacitors value, such controllers are known as VAR controllers.

Modern VAR controllers employ micro-controllers for measuring the voltages and

currents, compute the required value for the capacitors and switch properly the

electronic switches. The capacitance is varied in very fine amounts. The capacitance

will be varied considering different Power Factors.

Frequency Control

To keep constant the frequency it is necessary to keep the active power constant at its

rated value. As the loads of a MHP are variable by nature, the equilibrium cannot be

maintained:

• a variable dump load must be added into the circuit, in order to maintain the total

load constant.

• The balance can be reached by adjusting the input mechanical power, too.

However, such a solution implies a water turbine speed governor. The

mechanical adjustment is slow; it produces high mechanical and hydraulic stress

and is less reliable.

the dump load

• There are different solutions. Basically, a

power electronic controlled resistor is

employed as dump load.

Automatic control

Small hydro schemes and MHP are normally unattended and operated through an

automatic control system. Because not all power plants are alike, it is almost impossible

to determine the extent of automation that should be included in a given system, but

some requirements are of general application :

a) All equipment must be provided with manual controls and meters totally independent

of the programmable controller to be used only for initial start up and for maintenance

procedures.

b) The system must include the necessary relays and devices to detect malfunctioning

of a serious nature and then act to bring the unit or the entire plant to a safe de-

energised condition.

c) Relevant operational data of the plant should be collected and made readily available

for making operating decisions, and stored in a database for later evaluation of plant

performance, SCADA.

d) An intelligent control system should be included to allow for full plant operation in an

unattended environment.

e) It must be possible to access the control system from a remote location and override

any automatic decisions.

f) The system should be able to communicate with similar units, up and downstream, for

the purpose of optimising operating procedures.

g) Fault anticipation constitutes an enhancement to the control system. Using an expert

system, SCADA, fed with baseline operational data, it is possible to anticipate faults

before they occur and take corrective action so that the fault does not occur.

The system must be configured by modules:

• An analogue-to-digital conversion module for measurement of water level,

wicket-gate position, blade angles, instantaneous power output, temperatures,

etc.

• A digital-to-analogue converter module to drive hydraulic valves, chart recorders,

etc.

• A counter module to count generated kWh pulses, rain gauge pulses, flow

pulses, etc.

• a ―smart― telemetry module providing the interface for offsite communications,

via dial-up telephone lines or radio link.

• modular software allows for easy maintenance.

This modular system approach is well suited to the widely varying requirements

encountered in hydropower control, and permits both hardware and software to be

standardised. Cost reduction can be realised through the use of a standard system.

• Automatic control systems can significantly reduce the cost of energy production

by reducing maintenance and increasing reliability, while running the turbines

more efficiently and producing more energy from the available water.

• With the tremendous development of desktop computers, their prices are now

very low. The new programming techniques -Visual Basic, Delphi etc- assist the

writing of software using well-established routines; the GUI interfaces, that every

body knows thanks to the Windows applications; everything has contributed to

erase the old aura of mystery that surrounded the automatic control applications.

Environmental impact

• Electricity production in SHP and MHP is environmentally rewarding.

• In sensitive areas, local impacts are not always negligible. The significant global

advantages of small hydropower must not prevent the identification of burdens

and impacts at local level nor the taking of necessary mitigation actions.

• On the other hand because of their economic relevance, thermal plants are

authorised at very high administrative levels, although some of their impacts

cannot be mitigated at present. A small hydropower scheme producing impacts

that almost always can be mitigated is considered at lower administrative levels,

where the influence of pressure groups - angling associations, ecologists, etc.- is

greater.

• It is not difficult to identify the impacts, but to decide which mitigation measures

should be undertaken it is not easy, because these are usually dictated by

subjective arguments. It is therefore strongly recommended to establish a

permanent dialogue with the environmental authorities as a very first step in the

design phase.

Economic Analysis

• The estimation of the investment cost constitutes the first step of an economic

evaluation. For a preliminary approach the estimation can be based on the cost

of similar schemes .

• In its recent publications ESHA analyses the cost of the different components of

a scheme -weir, water intake, canal, penstock, power-house, turbines and

generators, transformers and transmission lines.

• A cost estimate is essential for economic analysis.

• it is necessary as a second step, to make a preliminary design including the

principal components of the scheme.

• Based on this design, budget prices for the materials can be obtained from

suppliers. Such prices cannot be considered as firm prices until specifications

and delivery dates have been provided. This will come later, during the actual

design and procurement process.

• Anyhow , a sound economic analysis must be performed regarding the ultimate

economic efficiency of the SHP or MHP.

Conclusions: the advantages of Small and MHP

• It is the most concentrated energy source between the RES;

• The available energy is predictable;

• The available power is continuously on demand;

• Only limited maintenance is required;

• It is a long-lasting technology and its performances are still object of

improvement.

The main disadvantages

• It is a very site-specific technology;

• So it requires a great deal of experience from the designer, not available always;

• The useful power is limited by the available flow. It is not possible to expand the

power.

NUCLEAR POWER PLANTS

Categories

More than 442 nuclear power plants operate around the world (375,001 MW) and

65 in construction.

The modern nuclear plant size varies from 100 to 1200 MW.

• Close to 300 operate pressurized water reactors (PWRs)

• more than 100 are built with boiling-water reactors (BWRs),

• 50 use gas-cooled reactors,

• the rest are heavy-water reactors. These reactors are built for better utilization of

uranium fuel.

PWR Pressurized Water Reactor

BWR Boiling Water Reactors

The general arrangement

Pressurized Water Reactor

Water Circuit

• The reactor heats the water from about 290 to about 350 ° C. High pressure, at

about 2235 psi, prevents boiling. Pressure is maintained by a pressurizer, and

the water is circulated by a pump through a heat exchanger.

• Cooling water enters the reactor from the bottom, flows through the core, and is

heated by nuclear fission.

• The heat exchanger evaporates the feedwater and generates steam, which

supplies a system similar to a conventional power plant. The advantage of this

two-loop system is the separation of the potentially radioactive reactor cooling

fluid from the water-steam system.

The reactor core

• The fuel and control rod assembly is located in the lower part.

• The steam separators are above the core, and the steam dryers are at the top of

the reactor.

• The reactor is enclosed by a steel case and then in a concrete dome.

CANDU reactor : PHWR= Pressurised heavy water reactor

• Deuterium based nuclear reactors

• A pressurised heavy water reactor (PHWR) is a nuclear power reactor that uses

unenriched natural uranium as its fuel and heavy water as a moderator

(deuterium oxide D2O).

• The heavy water is kept under pressure in order to raise its boiling point, allowing

it to be heated to higher temperatures and thereby carry more heat out of the

reactor core.

• While heavy water is expensive, the reactor can operate without expensive fuel

enrichment facilities thus balancing the costs.

CANDU Reactor

Water Circuit

A CANDU reactor is similar to

most "classic" nuclear power plants

in design. Fission reactions in the

reactor core heat a fluid, in this case

heavy water, which is kept under

high pressure to raise its boiling

point and avoid significant steam

formation in the core. The hot heavy water generated in this primary cooling loop is

passed into a heat exchanger heating light (ordinary) water in the less-pressurized

secondary cooling loop. This water turns to steam and powers a conventional turbine

with a generator attached to it.

The reactor core

• Heavy water is contained in a large tank called a calandria.

• Several hundred horizontal or vertical pressure tubes form channels for the fuel

penetrate the calandria, which contain the nuclear fuel and are a part of the

primary heat transport loop.

• The heat transport fluid flowing through the pressure tubes and the heavy water

in the calandria are separate and do not mix.

• As in the pressurised light water reactor, the primary coolant generates steam in

a secondary circuit to drive the turbines.

• The pressure tubes containing the fuel rods can be individually opened, and the

fuel rods changed without taking the reactor out of service. This reactor has the

least down-time of any known type.

Nuclear Waste: The Dilemma

• Nuclear waste is the type of waste that results from the use and production of

nuclear materials. As nuclear materials are produced and used up, one by-

product of the process is a large amount of dangerous chemical elements.

• Plutonium is the most dangerous of these. Plutonium is highly radioactive and

has a half-life of 25,000 years. This means that plutonium takes approximately

25,000 years to decay to half of its original potency.

• The immediate and long-term threats of radioactivity include causing cancer or

genetic damage in humans and animals; large amounts lead directly to radiation

sickness and death.

Radioactivitatea

• Când atomul de uraniu fisionează, generează doi sau trei neutroni. Mare parte

din neutronii produși astfel loves alți atomi de uraniu și mențin reacția în lanț, dar

câțiva dintre aceștia pot ajunge în apă sau în aerul din apa care se află în

reactor.Când un element care nu este radioactiv (deci este stabil) va capta un

neutron, el devine radioactiv. Însă acesta va scăpa repede de neutronul

suplimentar și va înceta să fie radioactiv in timpi de ordinul secundelor.

Fukushima

• * Radiație nucleară a ajuns în mediu, în timpul ventilării vasului sub presiune, dar

toți izotopii radioactivi din aburul ajuns în atmosferă au dispărut deja. A fost

eliberată în atmosferă și o cantitate redusă de cesiu și iod radioactiv. Atât de

redusă încât dacă ați fi stat deasupra coșului centralei în acest timp, ar trebui să

vă lăsați de fumat pentru a avea din nou o speranță de viață apropiată de medie.

Izotopii de iod și cesiu au fost diluați de apa mării.

* Primul compartiment a fost avariat, ceea ce înseamnă cu urme de cesiu și iod

vor ajunge în agentul de răcire, dar nu și uraniu. Există instalații pentru tratarea

acestei ape în al treilea compartiment, cesiul și iodul radioactiv va fi extras și

depus în zona de deșeuri nucleare, specifice oricărei centrale de acest tip.

* Apa de mare folosită pentru răcire a fost activată într-un oarecare grad.

Deoarece barele de control sunt inserate în reactor, reacția nucleară a uraniului

nu are loc, deci nu contribuie la activarea apei. Materialele radioactive

intermediare (cesiu și iod) nu mai sunt disponibile în această fază, deoarece

fisiunea uraniului s-a oprit de ceva vreme. Acest lucru reduce și mai mult

activarea radioactivă a apei. În concluzie, apa de mare folosită pentru răcire este

ușor radioactivă, dar acest lucru se va remedia în instalațiile specifice, înainte ca

apa să se întoarcă în natură.

* În timp, apa de mare va fi înlocuită cu agent de răcire normal (apă pură)

Power Transformers

electric power transformer

• The electric power transformer is a major power system component which

provides the capability of reliably and efficiently changing (transforming) ac

voltage and current at high power levels.

• Because electrical power is proportional to the product of voltage and current, for

a specified power level, low current levels can exist only at high voltage, and vice

versa.

The Transformer Core

The core of the power TRANSFORMER is usually made of laminated cold-rolled

magnetic steel that is grain oriented such that the rolling direction is the same as that of

the flux lines.

This type of core construction tends to reduce the eddy current and hysteresis

losses.

Core loss

• The eddy current loss Pe is proportional to the square of the product of the

maximum flux density BM(T), the frequency f (Hz), and thickness t (m) of the

individual steel lamination.

Pe = Ke(BM tf) (W)

Ke is dependent upon the core dimensions, the specific resistance of a

lamination sheet, and the mass of the core.

• The hysteresis power loss

Ph=Kh f BM (W)

In above, n is the Steinmetz constant (1.5 < n< 2.5) and Kh is a constant

dependent upon the nature of core material

Core loss

The core loss therefore is Pe = Pe+Ph

Core and Shell Types

Transformers are constructed in either a

shell or a core structure. Single phase power

transformer :

Transformer Windings

The windings of the power transformer may be either copper or aluminum.

These conductors are usually made of conductors having a circular cross

section; however, larger cross-sectional area conductors may require a rectangular

cross section for efficient use of winding space.

Transformer ratio: V1=(N1/N2)V2

• Multiwinding transformers, as well as polyphase transformers, can be made in

either shell- or core-type designs:

Electric diagrams

life of a transformer

• The life of a transformer insulation system depends, to a large extent, upon its

temperature.

• The total temperature is the sum of the ambient and the temperature rise. The

temperature rise in a transformer is intrinsic to that transformer at a fixed load.

The ambient temperature is controlled by the environment the transformer is

subjected to.

• The better the cooling system that is provided for the transformer, the higher the

―kVA‖ rating for the same ambient. For example, the kVA rating for a transformer

can be increased with forced air (fan) cooling. Forced oil and water cooling

systems are also used.

Three-Phase Transformers

• For Three-Phase distribution systems it is possible

to construct a device (called a three-phase

transformer) which allows the phase fluxes to

share common magnetic return paths. Such

designs allow considerable savings in core

material, and corresponding economies in cost,

size, and weight

MHD GENERATOR (magnetohydrodynamic)

The MHD (magnetohydrodynamic) generator transforms thermal energy or

kinetic energy directly into electricity. An advantage of MHD generators over

traditional electrical generators is they operate with few moving parts. This

technology is applicable to power generation and engine applications.

The MHD generator uses the motion of fluid or plasma to generate the currents

which generate the electrical energy. The mechanical generator , in contrast,

uses the motion of mechanical devices to accomplish this.

MHD generators are now practical for fossil fuels, but have been overtaken by

other, less expensive technologies for new plants. The unique value of MHD is

that it permits an older plant to be upgraded to high efficiency.

Principle

The Lorentz Force Law describes the effects of a charged particle moving in a constant

magnetic field. The simplest form of this law is given by the equation.

F = QxVxB

Where:

• F is the force acting on the particle (vector)

• v is velocity of particle (vector)

• Q is charge of particle (scalar)

• B is magnetic field (vector)

An example implementation would consist of a pipe or tube of some non-conductive

material. When an electrically conductive fluid flows through the tube, in the presence of

a significant perpendicular magnetic field, a charge is induced in the field, which can be

drawn off as electrical power by placing the electrodes on the sides at 90 degree angles

to the magnetic field.

• 1. principle one MHD-generator hot gas, about 3000

K

• 2. electrodes

• 3. isolation

• 4. magnetic poles

• 5. exhaust gas, about 2000 K

Generator efficiency

• The efficiency of the magnetohydrodynamic generator in a single stage is

estimated to be no greater than 10 to 20 percent. This makes it unattractive, by

itself, for power generation. However it has a number of places that it would be

an ideal fit in series with other forms of power generation.

• In series with a fossil fuel power plant a MHD generator could provide an

efficiency boost. By routing the exhaust gases of such a plant through a

magnetohydrodynamic generator before traditional thermal to electrical

conversion plants, it is estimated that one can convert fossil fuels into electricity

with an estimated efficiency of up to 65 percent.

• Similarly, the employment of a magnetohydrodynamic generator is conceivable in

series with a Nuclear reactor (either fission or fusion). Reactors of this type tend

to operate with fuel rod temperatures at approximately 2000 °C. By pumping the

reactor coolant through a magnetohydrodynamic generator before a traditional

heat exchanger is reached an estimated efficiency of 60 percent can be realized.

1: Coal dust

2: Combustion chamber

3: Combustion air

4: Nozzle

5: Electrodes

6: Magnetic field perpendicularly to

the indication level

7: Air heater8: Steam generator

9: Chimney

10-11 Turbine

12: Condenser

13: Air compressor

14: Alternator

15: Converter/Transformer

16: Delivered electrical achievement

Industrial MHD generator

Advantages:

• for adjusting the phase points - quick movable parts

• gas temperature of 3000°C

• high efficiency,

• reaction to load changes

• in electricity mains

Disadvantages:

• large material difficulties

• large supplies outputs of 10 MW or more (direct current has about 100V)

• outlet temperature of the gas with 2000°C

• high capital outlays

Technical problems

• The employment of the MHD generator for large scale mass energy conversion

failed so far because of the economics and chemistry. A certain amount of

electricity is required to maintain sustained magnetic flux density over 1.0 tesla

(T). Because of the high temperatures, the walls of the channel must be

constructed from an exceedingly heat-resistant substance such as yttrium oxide

or zirconium dioxide to retard oxidation. Similarly, the electrodes must be both

conductive and heat-resistant at high temperatures, making tungsten a good

choice.

Toxic byproducts

• If some form of liquefied metal is used in the operation of a MHD generator,

severe care must be taken with the form of cooling used on the electomagnetics

and in the channel. Aside from the chemical byproducts of heated electrified

alkali metals and channel material. The alkali metals themselves are highly, even

violently reactive with water.

• Measures must also be taken to separate any ionizing substance used, from the

exhaust gasses if the MHD generator is run on plasma.

• Natural MHD generators are an active area of research in plasma physics and

are of great interest to the geophysics and astrophysics communities. From their

perspective the earth is a global MHD generator and with the aid of the particles

on the solar wind produces the aurora borealis.

• The differently charged electromagnetic layers produced by the generator effect

on the earth's geomagnetic field enable the appearance of the aurora borealis.

As power is extracted from the plasma of the solar wind, the particles slow and

are drawn down along the field lines in a brilliant display over the poles.

Sustainability

systemic concept

• Sustainability is a systemic concept, relating to the continuity of economic,

social, institutional and environmental aspects of human society.

• It is intended to be a means of configuring civilization and human activity so that

society, its members and its economies are able to meet their needs and express

their greatest potential in the present, while preserving biodiversity and natural

ecosystems, and planning and acting for the ability to maintain these ideals

indefinitely.

• Sustainability affects every level of organization, from the local neighborhood to

the entire planet.

Sustainability: Definition in words

• Sustainability can be defined both qualitatively in words, and more quantitatively

rigorous as a ratio. Put in qualitative terms, sustainability seeks to provide the

best of all possible worlds for people and the environment both now and into the

indefinite future.

• In the terms of the 1987 Brundtland Report, sustainable development is

development that: "Meeting the needs of the present generation without

compromising the ability of future generations to meet their needs."

sustainable development

• The original term was "sustainable development", a term adopted by the Agenda

21 program of the United Nations. Some people now consider the term

"sustainable development" as too closely linked with continued physical

development, and prefer to use terms like "Sustainability",

"Sustainable Prosperity" and "Sustainable Genuine Progress" as the umbrella

terms.

common principles to achieve sustainable development

A number of common principles are embedded in most action programmes to

achieve sustainable development:

• dealing cautiously with risk, uncertainty and irreversibility;

• ensuring appropriate valuation, appreciation and restoration of nature;

• integration of environmental, social and economic goals in policies and activities;

• equal opportunity and community participation;

• conservation of biodiversity and ecological integrity;

common principles to achieve sustainable development

• ensuring inter-generational equity;

• recognizing the global dimension;

• a commitment to best practice;

• no net loss of human or natural capital;

• the principle of continuous improvement; and

• the need for good governance.

Concepts and issues

• There are two related categories of thought on environmental sustainability.

• In 1968 the Club of Rome, a group of European economists and scientists, was

formed. In 1972 they published Limits to Growth. Criticized by economists of the

time, the report predicted dire consequences because humans were using up the

Earth's resources and it advocated as one solution the abandonment of

economic development.

• In a different category, other groups formed to focus less on population—growth

control and slowing economic development and more on establishing

environmental standards and enforcement.

• At the heart of the concept of sustainability there is a fundamental,

immutable value set that is best stated as 'parallel care and respect for the

ecosystem and for the people within.' From this value set emerges the goal of

sustainability:

• to achieve human and ecosystem well-being together

success of any project or design

• It follows that the 'result' against which the success of any project or design

should be judged is the achievement of, or the contribution to, human and

ecosystem well-being together.

• It is a positive concept that has as much to do with achieving well-being for

people and ecosystems as it has to do with reducing stress or impacts.

sustainability models

In recognition that the Earth is finite, there has been a growing awareness that

there must be limits to certain kinds of human activity if life on the planet is to survive

indefinitely. In order to distinguish which activities are destructive and which are benign

or beneficial, various models have been developed. Such models include: life cycle

assessment and ecological footprint analysis. Recently the algorithms of the ecological

footprint model have been used in combination with the emergy methodology and a

sustainability index has also been derived from the latter.

Overpopulation

One of the critically important issues in sustainability is that of human

overpopulation. A number of studies have suggested that the current population of the

Earth, already over six billion, is too many people for our planet to support sustainably.

A number of organizations are working to try to reduce population growth, but some fear

that it may already be too late.

Types of sustainability - Institutional sustainability:

Can the strengthened institutional structure continue to deliver the results of the

technical cooperation to the ultimate end-users?

The results may not be sustainable if, for example, the planning unit

strengthened by the technical cooperation ceases to have access to top-management

or is not provided with adequate resources for the effective performance after the

technical cooperation terminated. Note that institutional sustainability can also be linked

to the concept of social sustainability, how the interventions can be sustained by social

structures and institutions .

Economical and financial sustainability:

Can the results of the technical cooperation continue to yield an economic benefit

after the technical cooperation is withdrawn?

For example, the benefits from the introduction of new crops may not be

sustained, if the constraints to marketing the crops are not resolved. Similarly,

economic (distinct from financial) sustainability may be at risk, if the end-users

continue to depend on heavily-subsidized activities and inputs.

Ecological sustainability:

Are the benefits to be generated by the technical cooperation likely to lead to a

deterioration in the physical environment (thus indirectly contributing to a fall in

production) or well-being of the groups targeted and their society?

Development sustainability

A definition of development sustainability is the continuation of benefits after

major assistance from the donor has been completed.

Ensuring that development projects are sustainable can reduce the likelihood of

them collapsing after they have just finished; it also reduces the throwing of money at

development problems and the subsequent social problems, such as dependence of the

stakeholders on external donors and their resources.

ten key factors influence development sustainability

There are ten key factors that influence development sustainability:

• Participation and ownership. Get the stakeholders (men and women) to

genuinely participate in design and implementation. Build on their initiatives and

demands. get them to monitor the project and periodically evaluate it for results.

• Capacity building and training. Training stakeholders to take over should begin

from the start of any project and continue throughout. The right approach should

both motivate and transfer skills to men and women.

• Government policies. Development projects should be aligned with local

government policies.

• Financial. In some countries and sectors financial sustainability is diff icult in the

medium-term. Training in local fundraising is a possibility, as is identifying

complementarity with the private sector, user pays approaches, and encouraging

policy reforms.

• Management and organisation. Activities that integrate with or build onto local

structures may have better prospects for sustainability than those which establish

new or parallel structures.

• Social, gender and culture. The introduction of new ideas, technologies and skills

requires an understanding of local decision-making systems, gender divisions

and cultural preferences.

• Technology. All outside equipment must be selected carefully considering the

local finance available for maintenance and replacement. Cultural acceptability

and the local capacity to maintain equipment and buy spare parts are key factors.

• Environment. Poor non-urban communities that depend on natural resources

should be involved in identifying and managing environmental risks. Urban

communities should identify and manage waste disposal and pollution risks.

• External political and economic factors. In a weak economy, projects should not

be too complicated, ambitious or expensive.

• Realistic duration. A short project may be inadequate for solving entrenched

problems in a sustainable way, particularly when behavioural and institutional

changes are intended. A long project, may on the other hand, promote

dependence.

Sustainable development

Sustainable development is a process of developing (land, cities, business,

communities, etc) that "meets the needs of the present without compromising the ability

of future generations to meet their own needs" according to the Brundtland Report.

Environmental degradation

Environmental degradation refers to the diminishment of a local ecosystem or the

biosphere as a whole due to human activity. Environmental degradation occurs when

nature's resources (such as trees, habitat, earth, water, air) are being consumed faster

than nature can replenish them. An unsustainable situation occurs when natural capital

(the sum total of nature‘s resources), is used up faster than it can be replenished.

Sustainability

Human activity, at a minimum, only uses nature's resources to the point where

they can be replenished naturally:

• Human consumption of renewable resources > Nature's ability to replenish:

Environmental degradation

• Human consumption of renewable resources = Nature's ability to replenish:

Environmental equilibrium / sustainable growth.

• Human consumption of renewable resources < Nature's ability to replenish:

Environmental renewal / also sustainable growth.

The long term final result of environmental degradation will be local environments

that are no longer able to sustain human populations.

ECOLOGY, POLLUTION AND SUSTAINABLE DEVELOPMENT

Ecology Definition

1.The scientific study of the relationships between plants, animals, and their

environment.

2.The study of the detrimental effects of modern civilization on the environment, with a

view toward prevention or reversal through conservation.

categorizations

Ecology is a broad biological science and can thus be divided into many sub-disciplines using

various criteria.

One such categorization, based on overall complexity (from the least complex to the

most), is:

• Behavioral ecology, which studies the ecological and evolutionary basis for

animal behavior, focusing largely at the level of the individual;

• Population ecology (or autecology), which deals with the dynamics of populations

within species, and the interactions of these populations with environmental

factors;

• Community ecology (or synecology) which studies the interactions between

species within an ecological community;

• Ecosystem ecology, which studies how flows of energy and matter interact with

biotic elements of ecosystems;

Ecology can also be classified on the basis of:

• the primary kinds of organism under study, e.g. animal ecology, plant ecology,

insect ecology;

• the biomes principally studied, e.g. forest ecology, grassland ecology, desert

ecology, benthic ecology;

• the geographic or climatic area, e.g. arctic ecology, tropical ecology

• the spatial scale under consideration, e.g. molecular ecology, macroecology,

landscape ecology;

Specialized branches of ecology

• Specialized branches of ecology include, among others:

• applied ecology, the practice of employing ecological principles and

understanding to solve real world problems (includes agroecology and

conservation biology);

• biogeography, the study of the geographic distributions of species ;

• chemical ecology, which deals with the ecological role of biological chemicals

used in a wide range of areas including defense against predators and attraction

of mates;

• conservation ecology, which studies how to reduce the risk of species extinction;

• ecological succession, which focuses on understanding directed vegetation

change;

• ecotoxicology, which looks at the ecological role of toxic chemicals (often

pollutants, but also naturally occurring compounds);

• evolutionary ecology or ecoevolution which looks at evolutionary changes in the

context of the populations and communities in which the organisms exist;

and so on…

Ecological Engineering

• Ecological Engineering is the emerging field of the use of ecological processes

within natural or constructed imitation of natural systems to achieve engineering

goals.

• Ecological Engineering is "the design of sustainable ecosystems that integrate

human society with its natural environment for the benefit of both" (Mitsch, 1998).

self-designing capacity of nature

Ecological Engineering is based on the self-designing capacity of nature to take

ecosystems to sustainable optimum states. Past engineering approaches overuse fossil

fuels and require intensive maintenance because they are out of balance with nature.

Ecological engineering solutions rely more on natural energy flows (solar-based) and

are often very low maintenance, when done correctly.

Examples of ecological engineering

• The restoration of a landscape or the creation of a wetland ecosystem to treat

wastewater. In the case of restoring a landscape denuded of all soil by erosion,

the ecological engineer would approach the problem not by trucking in tons of

soil, he or she would work to establish soil-building organisms to do the work.

• In the case of wastewater treatment, the conventional engineer would use

electricity to pump and aerate the water while dumping in tons of chemicals. The

ecological engineer would use the natural assimilative capacity of certain plants

and microbes to remove the pollutants of concern in a gravity-flow system.

• To design equipments with reusable parts and involving less environmental

harmful materials = ecological design, ex replace cadmium or mercury in electric

batteries with metal hydrate or lithium ion .

ecological footprint

• An ecological footprint is the amount of land and water area a human

population would need to provide the resources required to sustainably support

itself and to absorb its wastes, given prevailing technology. The term was first

coined in 1996 by Canadian ecologist William Rees and Mathis Wackernagel (a

grad student working under Rees at the University of British Columbia at the

time).

• Footprinting is now widely used around the globe as an indicator of

environmental sustainability. It can be used to measure and manage the use of

resources throughout the economy. It is commonly used to explore the

sustainability of individual lifestyles, goods and services, organisations, industry

sectors, regions and nations.

inter-disciplinary fields

Ecology also plays important roles in many inter-disciplinary fields:

• ecological design and ecological engineering.

• ecological economics.

• human ecology and ecological anthropology.

• social ecology, ecological health and environmental psychology.

Finally, ecology has also inspired (and lent its name to) other non-biological disciplines

such as

• industrial ecology.

• software ecology and information ecology.

Pollution

Definition: The contamination of the air, water, or earth by harmful or potentially harmful

substances

During the industrial revolution of the nineteenth century, the mass production of

goods created harmful wastes, much of which was dumped into rivers and streams.

The twentieth century saw the popular acceptance of the automobile and the

internal combustion engine, which led to the pollution of the air.

Rapidly expanding urban centers began to use rivers and lakes as repositories

for sewage.

The Environmental movement in the 1960s emerged from concerns that air,

water, and soil were being polluted by harmful chemicals and other toxic substances.

Land pollution involves the depositing of solid wastes that are useless,

unwanted, or hazardous. Types of solid waste include garbage, rubbish, ashes,

sewage-treatment solids, industrial wastes, mining wastes, and agricultural wastes.

Most solid waste is buried in sanitary landfills. A small percentage of municipalities

incinerate their refuse, while composting is rarely employed.

Landfills - Modern landfills attempt to minimize pollution of surface and groundwater.

They are now located in areas that will not flood and that have the proper type of soil.

Solid wastes are compacted in the landfill and are vented to eliminate the buildup of

dangerous gases.

Hazardous wastes

Hazardous wastes, including toxic chemicals and flammable, radioactive, or

biological substances, cannot be deposited in landfills, and the management of these

wastes is subject to federal and state regulation. Governments are promoting

comprehensive regulatory statutes that create a "cradle to grave" systems of controlling

the entire hazardous waste life cycle.

Nuclear wastes are especially troublesome .

recovering resources

Solid waste pollution has been reduced by recovering resources rather than

burying them. Resource recovery includes massive systems that burn waste to produce

steam, but it also includes the recycling of glass, metal, and paper from individual

consumers and businesses. The elimination of these kinds of materials from landfills

has prevented pollution and extended the period during which landfills can receive

waste.

accumulation of chemicals

Land pollution also involves the accumulation of chemicals in the ground. Modern

agriculture, which has grown dependent on chemical fertilizers and chemicals that kill

insects, has introduced substances into the soil that kill more than pests. For many

years the chemical DDT was routinely sprayed on crops to control pests. It was banned

when scientists discovered that the chemical entered the food chain and was harming

wildlife and possibly humans.

Water pollution is a large set of adverse effects upon water bodies such as lakes,

rivers, oceans, and groundwater caused by human activities.

Although natural phenomena such as volcanoes, algae blooms, storms, and

earthquakes also cause major changes in water quality and the ecological status

of water, these are not deemed to be pollution. Water pollution has many causes

and characteristics. Increases in nutrient loading may lead to eutrophication.

Organic wastes such as sewage impose high oxygen demands on the receiving

water leading to oxygen depletion with potentially severe impacts on the whole

eco-system. Industries discharge a variety of pollutants in their wastewater

including heavy metals, organic toxins, oils, nutrients, and solids. Discharges can

also have thermal effects, especially those from power stations, and these too

reduce the available oxygen. Silt-bearing runoff from many activities including

construction sites, deforestation and agriculture can inhibit the penetration of

sunlight through the water column, restricting photosynthesis and causing

blanketing of the lake or river bed, in turn damaging ecological systems.

Pollutants in water include a wide spectrum of chemicals, pathogens, and

physical chemistry or sensory changes. Many of the chemical substances are

toxic. Pathogens can obviously produce waterborne diseases in either human or

animal hosts. Alteration of water's physical chemistry include acidity, conductivity,

temperature, and eutrophication. Eutrophication is the fertilisation of surface

water by nutrients that were previously scarce. Even many of the municipal water

supplies in developed countries can present health risks. Water pollution is a

major problem in the global context. It has been suggested that it is the leading

worldwide cause of deaths and diseases, and that it accounts for the deaths of

more than 14,000 people daily.

Sources of water pollution

Some of the principal sources of water pollution are:

geology of aquifers from which groundwater is abstracted

industrial discharge of chemical wastes and byproducts

discharge of poorly-treated or untreated sewage

surface runoff containing pesticides or fertilizers

slash and burn farming practice, which is often an element within shifting

cultivation agricultural systems

surface runoff containing spilled petroleum products

surface runoff from construction sites, farms, or paved and other impervious

surfaces e.g. silt

discharge of contaminated and/or heated water used for industrial processes

acid rain caused by industrial discharge of sulfur dioxide (by burning high-sulfur

fossil fuels)

excess nutrients added (eutrophication) by runoff containing detergents or

fertilizers

underground storage tank leakage, leading to soil contamination, thence aquifer

contamination

Contaminants

Contaminants may include organic and inorganic substances.

Some organic water pollutants are:

insecticides and herbicides, a huge range of organohalide and other chemicals

bacteria, often is from sewage or livestock operations;

food processing waste, including pathogens

tree and brush debris from logging operations

VOCs (Volatile Organic Compounds, industrial solvents) from improper storage

Some inorganic water pollutants include:

heavy metals including acid mine drainage

acidity caused by industrial discharges (especially sulfur dioxide from power

plants)

chemical waste as industrial by products

fertilizers, in runoff from agriculture including nitrates and phosphates

silt in surface runoff from construction sites, logging, slash and burn practices or

land clearing sites

Effects of water pollution

The effects of water pollution are not only devastating to people but also to

animals, fish, and birds. Polluted water is unsuitable for drinking, recreation,

agriculture, and industry. It diminishes the aesthetic quality of lakes and rivers.

More seriously, contaminated water destroys aquatic life and reduces its

reproductive ability. Eventually, it is a hazard to human health. Nobody can

escape the effects of water pollution.

The individual and the community can help minimize water pollution. By simple

housekeeping and management practices the amount of waste generated can be

minimized.

Transport and chemical reactions of water pollutants

Most water pollutants are eventually carried by the rivers into the oceans. In

some areas of the world the influence can be traced hundred miles from the

mouth by studies using hydrology transport models. Advanced computer models

such as SWMM or the DSSAM Model have been used in many locations

worldwide to examine the fate of pollutants in aquatic systems.

The big gyres in the oceans trap floating plastic debris. The North Pacific Gyre

for example has collected the so-called Great Pacific Garbage Patch that is now

about the size of Texas. Many of these long-lasting pieces wind up in the

stomachs of marine birds and animals.

Many chemicals undergo reactive decay or change especially over long periods

of time in groundwater reservoirs. A noteworthy class of such chemicals are the

chlorinated hydrocarbons such as trichloroethylene (used in industrial metal

degreasing) and tetrachloroethylene used in the dry cleaning industry. Both of

these chemicals, which are carcinogens themselves, undergo partial

decomposition reactions, leading to new hazardous chemicals.

Romania:

Resurse de apa:

o apele de suprafaţă – râuri interioare, lacuri naturale sau artificiale, fluviul

Dunărea (apele Mării Negre nu sunt luate în considerare datorită dificultăţilor

tehnice şi economice de desalinizare )

o apele subterane.

În ciuda aparenţelor din unele zone, România nu este o ţară bogată în resursele de

apă, ocupând locul 21 în Europa (cf. Statisticii Naţiunilor Unite) în condiţiile în care

dispune de numai 1700 m 3 de apă timp de un an pentru un locuitor.

SITUAŢIA APELOR ROMÂNIEI DIN PUNCT DE VEDERE AL POLUĂRII

Starea actuală a factorilor de mediu în ţara noastră, deosebit de critică, în

special, în zonele afectate de activităţi antropice, necesită ample acţiuni pentru

reducerea substanţială a potenţialului poluant şi pentru refacerea ecosistemelor

afectate.

Deşi în ultimii 20 de ani au fost alocate fonduri pentru instalaţii antipoluante,

ajungându-se în prezent să funcţioneze peste 4900 de staţii de epurare a apei şi peste

15000 de instalaţii de purificare a gazelor evacuate din procesele tehnologice,

contribuţia acestora la reducerea poluării mediului a fost insuficientă datorită:

o - exploatării necorespunzătoare a instalaţiilor, lipsa pieselor de schimb,

reducerea cotelor de energie şi fiabilitatea redusă a unor utilaje;

o - lipsa personalului calificat, ca şi retribuirea lui la un nivel minim faţă de alte

ramuri, reprezintă o altă cauză care a contribuit la apariţia unor deficienţe majore

în funcţionarea la parametrii proiectaţi a acestor instalaţii;

o - dezvoltarea capacităţii de producţie fără asigurarea concomitentă a realizării

instalaţiilor de epurare şi respectiv de purificare a gazelor nocive.

Poluarea reţelei hidrografice a dus la dispariţia faunei pe segmente importante de

râu, de exemplu: Ialomiţa 48%, Olt 42%, Tisa 35%, Siret 31%, Argeş 22%, Mureş 22%,

Vedea 23%, Prut 20%.

o Oltul este, se spune, o apă moartă. Bârsa îl sufocă, aducându-i substanţele

deversate de Fabrica de celuloză şi hârtie din Zărneşti. Alt afluent, Vulcăniţa,

aduce ―otravă‖ scursă de la Colorom Codlea. Combinatele chimice de la

Victoria şi Govora ―contribuie‖ sârguincioase cu substanţe organo-clorurate, la

fel de toxice. Multe asemenea întreprinderi nu au nici măcar autorizaţii de

funcţionare, iar staţiile de epurare, ce au costat milioane, zac nefolosite de ani de

zile.

o Râul Mureş, coloana vertebrală a Transilvaniei, este ameninţat să se rupă sub

apăsarea nemiloasă a industrializării. În aval de oraşul Reghin se deversează

cca 250 l/sec. apă uzată. În aval de localitatea Gorneşti, crescătoria de porci

amplifică poluarea, la care se adaugă şocul poluant al oraşului Tg. Mureş, 3,5

m3/oră apă uzată (menajeră şi industrială), care reprezintă 25-35% din volumul

total al debitului râului şi care conţine: compuşi ai azotului, fosfaţi, detergenţi,

fenoli. Aceşti poluanţi crează un şoc tragic echilibrului ecologic al râului Mureş,

alterându-i calităţile. Diminuarea oxigenului din apă duce la existenţa a doar

două grupe de viermi, puţin pretenţioşi la condiţiile de mediu.

Sistemul actual de dezinfectare a apei Mureş prin clorinare dă naştere la

trihalometani (substanţe cancerigene).

o Râul Târnava, victimă pe termen lung a poluării de aici, este de mult abiotic.

Coşurile celor două uzine domină cerul nu atât cu înălţimea lor, cât mai ales cu

negru de fum şi noxele ce le degajă continuu.

o Substanţele ucigătoare se varsă, toate, în Dunăre.

o “Dunărea este bolnavă”, spunea comandantul Cousteau, aflat în vizită la

Bucureşti şi nu este de mirare, căci adună tot răul de la munţii Pădurea Neagră

încoace. Iar noi sporim ―sinistra zestre‖. În judeţul Mehedinţi, pe parcursul a

179km, fluviul primeşte 11600 tone suspensii şi 1600 tone substanţe

biodegradabile pe care le duce spre mare.

o Adevărul despre Marea Neagră este trist, chiar dramatic. Uni experţi vorbesc

deja de o criză ecologică gravă, tot mai evidentă. Creşte continuu poluarea,

Dunărea fiind principalul cărăuş de reziduuri dintr-o Europă puternic

industrializată; la capătul drumului ei se află România şi Marea Neagră. Tot mai

frecvent şi pe zone tot mai întinse, apare fenomenul de hipozie – scăderea

concentraţiei de oxigen, element indispensabil vieţii. În plus, creşte, în anumite

lacuri, nivelul hidrogenului sulfurat, care împiedică viaţa.

o Marea Neagră prezintă particularitatea de a avea la suprafaţă un strat de apă

oxigenată, iar în adânc un altul cu hidrogen sulfurat, care nu permite decât

existenţa câtorva specii microbiologice. Scade dramatic biodiversitatea. Stridii nu

mai există demult în dreptul litoralului nostru, midiile aproape au dispărut, peştele

s-a împuţinat dramatic.

Impacts on fluvial, coastal and groundwater resources from organic pollution, nutrients

and hazardous substances (based on the 2004 National Analysis Year for the EU Water

Framework Directive)..

i) Permanent freshwater bodies: Of the 2347 identified, their status is as follows:

Type “At risk” “Possibly at risk” “Without risk”

Organic pollution 9.5% 5.5% 85%

Nutrient pollution 12.3% 7.3% 80.4%

Priority substances 2.4% 3.3% 94.3%

All categories 27.2% 15.8% 57%

ii) Transitional water bodies: Of the 6 bodies identified, their status is as follows:

Type “At risk” “Possibly at risk” “Without risk”

Organic pollution 1 5 0

Nutrient pollution 6 0 0

Priority substances 3 2 1

iii) Coastal waters: Of the 3 bodies identified, their status is as follows:

Type “At risk” “Possibly at risk” “Without risk”

Organic pollution 0 1 2

Nutrient pollution 3 0 0

Priority substances 0 2 1

iv) Groundwater bodies: Of the 129 bodies identified (19 of which are transboundary),

20 are considered to be ―at risk‖ – see table below:

Type “At risk” “Possibly at risk” “Without risk”

Organic pollution 4 - -

Nutrient pollution 14 - -

Priority substances 2 - -