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Course for energy sources
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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 - -