modern electric power supply systems


modern electric power supply systems
M.Yousuf Siddqui
Bilal Ahmed
Waseem Ikram
Group # 3
Section B
Electricity generation is the process of generating electric power from sources of energy. The
fundamental principles of electricity generation were discovered during the 1820s and early
1830s by the British scientist Michael Faraday. His basic method is still used today: electricity is
generated by the movement of a loop of wire, or disc of copper between the poles of a magnet.
For electric utilities, it is the first process in the delivery of electricity to consumers. The other
processes, electricity transmission, distribution, and electrical power storage and recovery
using pumped-storage methods are normally carried out by the electric power industry.
Electricity is most often generated at a power station by electromechanical generators,
primarily driven by engines fueled by chemical combustion or nuclear fission but also by other
means such as the kinetic energy of flowing water and wind. Other energy sources include
solar photovoltaic and geothermal power.
Central power stations became economically practical with the development of alternating
current power transmission, using power transformers to transmit power at high voltage and
with low loss. Electricity has been generated at central stations since 1881. The first power
plants were run on water power or coal, and today we rely mainly on coal, nuclear, natural
gas, hydroelectric, wind generators, and petroleum, with a small amount from solar
energy, tidal power, and geothermal sources.
The use of power-lines and power-poles has been significantly important in the distribution of
When you start out with electronics, you'll hear a lot about power supplies - they're in every
electronics project and they are the backbone of everything! A good power supply will make
your project hum along nicely. A bad power supply will make life frustrating: stuff will work
sometimes but not others, inconsistent results, motors not working, sensor data always off.
Understanding power supplies is the key to make things work.
Electric power systems are comprised of components that produce electrical energy and
transmit this energy to consumers. A modern electric power system has mainly six main
1) Power plants which generate electric power
2) Transformers which raise or lower the voltages as needed
3) Transmission lines to carry power
4) Substations at which the voltage is stepped down for carrying power over the distribution
5) Distribution lines
6) Distribution transformers which lower the voltage to the level needed for the consumer
equipment. The production and transmission of electricity is relatively efficient and
inexpensive, although unlike other forms of energy, electricity is not easily stored, and thus,
must be produced based on the demand.
Electricity in Pakistan is generated, transmitted, distributed and retail supplied by two vertically
integrated public sector utilities: Water and Power Development Authority (WAPDA) for all of
Pakistan (except Karachi), and the Karachi Electric Supply Corporation (KESC) for the city of
Karachi and its surrounding areas. There are around 20 independent power producers that
contribute significantly in electricity generation in Pakistan.
For years, the matter of balancing Pakistan's supply against the demand for electricity has
remained a largely unresolved matter. Pakistan faces a significant challenge in revamping its
network responsible for the supply of electricity. Electricity generation in Pakistan has shrunk
by up to 50% in recent years due to an over-reliance on fossil fuels. In 2008, availability of
power in Pakistan falls short of the population's needs by 15% Pakistan was hit by its worst
power crisis in 2007 when production fell by 6000 Megawatts and massive blackouts followed
suit. Load Shedding and power blackouts have become severe in Pakistan in recent years.
Electricity – total installed capacity: 21,000 MW (2011)
Electricity – Sources (2007)
fossil fuel – 12,580 MW – 65% of total
hydro – 6,463 MW – 33% of total
nuclear – 462 MW – 2% of total
There are four major power producers in country: WAPDA (Water & Power Development
Authority), KESC (Karachi Electric Supply Company), IPPs (Independent Power Producers) and
PAEC (Pakistan Atomic Energy Commission).
Electrical systems differ around the world - both in voltage and less critically, frequency. The
physical interface (plugs and sockets) are also different and often incompatible. However,
travellers with electrical appliances can take a few steps to ensure that they can be safely used
at their destination.
Total energy consumed at all power plants for the generation of electricity was 4,398,768 ktoe
(kilo ton of oil equivalent) which was 36% of the total for primary energy sources (TPES) of
Electricity output (gross) was 1,735,579 ktoe (20,185 TWh), efficiency was 39%, and the balance
of 61% was generated heat. A small part (145,141 ktoe, which was 3% of the input total) of the
heat was utilized at co-generation heat and power plants. The in-house consumption of
electricity and power transmission losses were 289,681 ktoe.
Source of Electricity (World total year 2008)
Nuclear Hydro other Total
Average electric power (TWh/year)
8,263 1,111 4,301
3,288 568
Average electric power (GW)
942.6 126.7 490.7
375.1 64.8
Electric power delivery throughout the United States was designated by the National Academy
of Engineering as the leading engineering development of the 20th century. Since electricity
was first delivered to private citizens in the late 19th century, the value of reliable electric
power to our economy has been obvious. Our world has been transformed by countless
technologies enabled by the widespread delivery of secure, high-quality electric
power. However, the transmission and distribution infrastructure in the United States is aging,
and the need for modernization has become urgent.
2020, a Different Kind of Power System
By 2020 USA anticipate that wind, water, and solar energy (WWS) will be dependably
integrated with efficient, conventional-fuel power plants that are cleaner than ever (Jacobson
and Delucchi, 2009). In addition, the transmission grid will be greatly expanded, and new
monitoring and control systems will help keep it reliable.
In individual homes, dishwashers and clothes washers, more efficient than ever, will turn on to
take advantage of low-cost power that the utility has signaled is available; hybrid electric cars
will also be recharged in off-peak hours. Electric outages will be very rare because intelligent
systems will identify deteriorating power-delivery apparatus and dispatch crews for
repair before outages occur. When a major fault or accident does happen, the electricity
system will automatically reconfigure itself and restore power with a barely noticeable blink of
the lights.
Widespread deployment of these advanced technologies is within their grasp. But to make
these systems economical, dependable, maintainable, and operationally independent of
excessive human oversight will require additional research and much good engineering. A
plentiful, educated, and experienced workforce is the key to USA’s electric-power future.
Composition of Electricity in USA by Resources (TWh per year 2008)
Fossil Fuel
Coal Oil Gas
2,133 58
911 3,101
Wind Tide
Hydropower provides about 96 percent of the renewable energy in the United States. Other
renewable resources include geothermal, wave power, tidal power, wind power, and solar
power. In Washington State hydroelectric power plants provided approximately 80 percent of
the electrical power during 2002. In contrast, in Ohio during the same year, almost 87 percent
of the electrical power came from coal-fired power plants due to the area’s ample supply of
A power supply is a device that supplies electric power to an electrical load. The term is most
commonly applied to electric power converters that convert one form of electrical energy to
another, though it may also refer to devices that convert another form of energy (mechanical,
chemical, solar) to electrical energy. A regulated power supply is one that controls the output
voltage or current to a specific value; the controlled value is held nearly constant despite
variations in either load current or the voltage supplied by the power supply's energy source.
Every power supply must obtain the energy it supplies to its load, as well as any energy it
consumes while performing that task, from an energy source. Depending on its design, a power
supply may obtain energy from:
Electrical energy transmission systems. Common examples of this include power
supplies that convert AC line voltage to DC voltage.
Energy storage devices such as batteries and fuel cells.
Electromechanical systems such as generators and alternators.
Solar power.
This is a massive power supply that's in a PC, usually you don’t see this unless you open up the
PC and look inside for the big metal box.
Power supplies for electronic devices can be broadly divided into line-frequency (or
"conventional") and switching power supplies. The line-frequency supply is usually a relatively
simple design, but it becomes increasingly bulky and heavy for high-current equipment due to
the need for large mains-frequency transformers and heat-sinked electronic regulation
circuitry. Conventional line-frequency power supplies are sometimes called "linear," but that is
not accurate because the conversion from AC voltage to DC is fundamentally non-linear when
the rectifiers feed into capacitive reservoirs. Linear voltage regulators produce regulated output
voltage by means of an active voltage divider that consumes energy, thus making efficiency
low. A switched-mode supply of the same rating as a line-frequency supply will be smaller, is
usually more efficient, but would be more complex.
 Battery: A battery is a device that converts stored chemical energy to electrical
energy. Batteries are commonly used as energy sources in many household and
industrial applications. There are two types of batteries: primary batteries (disposable
batteries), which are designed to be used once and discarded, and secondary batteries
(rechargeable batteries), which are designed to be recharged and used multiple times.
Batteries come in many sizes, from miniature cells used in hearing aids and
wristwatches to room-size battery banks that serve as backup power supplies in
telephone exchanges and computer data center.
DC Power Supply: An AC powered unregulated power supply usually uses a
transformer to convert the voltage from the wall outlet (mains) to a different, nowadays
usually lower, voltage. If it is used to produce DC, a rectifier is used to convert
alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or
more capacitors, resistors, and sometimes inductors, to filter out (smooth) most of the
pulsation. A small remaining unwanted alternating voltage component at mains or twice
mains power frequency (depending upon whether half- or full-wave rectification is
used)—ripple—is unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem, and the simplest
unregulated mains-powered DC power supply circuit consists of a transformer driving a
single diode in series with a resistor.
Before the introduction of solid-state electronics, equipment used valves (vacuum
tubes) which required high voltages; power supplies used step-up transformers,
rectifiers, and filters to generate one or more direct voltages of some hundreds of volts,
and a low alternating voltage for filaments. Only the most advanced equipment used
expensive and bulky regulated power supplies.
 AC Power Supply: An AC power supply typically takes the voltage from a wall outlet
(mains supply) and lowers it to the desired voltage. Some filtering may take place as
 Linear Regulated Power Supply: The voltage produced by an unregulated
power supply will vary depending on the load and on variations in the AC supply voltage.
For critical electronics applications a linear regulator may be used to set the voltage to a
precise value, stabilized against fluctuations in input voltage and load. The regulator also
greatly reduces the ripple and noise in the output direct current. Linear regulators often
provide current limiting, protecting the power supply and attached circuit from
AC/DC Supply: In the past, mains electricity was supplied as DC in some regions, AC
in others. Transformers cannot be used for DC, but a simple, cheap unregulated power
supply could run directly from either AC or DC mains without using a transformer. The
power supply consisted of a rectifier and a filter capacitor. When operating from DC, the
rectifier was essentially a conductor, having no effect; it was included to allow operation
from AC or DC without modification.
Computer Power Supply: A modern computer power supply is a switch-mode
power supply that converts AC power from the mains supply, to several DC voltages.
Switch-mode supplies replaced linear supplies due to cost, weight, and size
Welding Power Supply: Arc welding uses electricity to melt the surfaces of the
metals in order to join them together through coalescence. The electricity is provided by
a welding power supply, and can either be AC or DC. Arc welding typically requires high
currents typically between 100 and 350 amps. Some types of welding can use as few as
10 amps, while some applications of spot welding employ currents as high as 60,000
amps for an extremely short time. Older welding power supplies consisted of
transformers or engines driving generators. More recent supplies use semiconductors
and microprocessors reducing their size and weight.
Here is the power supply that is used in many apple products
An electric power system is a network of electrical components used to supply, transmit and
use electric power. An example of an electric power system is the network that supplies a
region's homes and industry with power - for sizable regions, this power system is known as the
grid and can be broadly divided into the generators that supply the power, the transmission
system that carries the power from the generating centres to the load centres and the
distribution system that feeds the power to nearby homes and industries. Smaller power
systems are also found in industry, hospitals, commercial buildings and homes. The majority of
these systems rely upon three-phase AC power - the standard for large-scale power
transmission and distribution across the modern world. Specialized power systems that do not
always rely upon three-phase AC power are found in aircraft, electric rail systems, ocean liners
and automobiles.
An electrical grid is an interconnected network for delivering electricity from suppliers to
consumers. It consists of generating stations that produce electrical power, high-voltage
transmission lines that carry power from distant sources to demand centers, and distribution
lines that connect individual customers.
Power stations may be located near a fuel source, at a dam site, or to take advantage of
renewable energy sources, and are often located away from heavily populated areas. They are
usually quite large to take advantage of the economies of scale. The electric power which is
generated is stepped up to a higher voltage-at which it connects to the transmission network.
The transmission network will move the power long distances, sometimes across international
boundaries, until it reaches its wholesale customer (usually the company that owns the local
distribution network).
On arrival at a substation, the power will be stepped down from a transmission level voltage to
a distribution level voltage. As it exits the substation, it enters the distribution wiring. Finally,
upon arrival at the service location, the power is stepped down again from the distribution
voltage to the required service voltage(s).
General layout of electricity networks, voltages and depictions of electrical lines are typical for
Germany and other European systems.
A power station (also referred to as a generating station, power plant, powerhouse or
generating plant) is an industrial facility for the generation of electric power. At the center of
nearly all power stations is a generator, a rotating machine that converts mechanical power
into electrical power by creating relative motion between a magnetic field and a conductor. The
energy source harnessed to turn the generator varies widely. It depends chiefly on which fuels
are easily available, cheap enough and on the types of technology that the power company has
access to. Most power stations in the world burn fossil fuels such as coal, oil, and natural gas to
generate electricity, and some use nuclear power, but there is an increasing use of cleaner
renewable sources such as solar, wind, wave and hydroelectric.
Thermal Power Stations: In thermal power stations, mechanical power is
produced by a heat engine that transforms thermal energy, often from combustion of a
fuel, into rotational energy. Most thermal power stations produce steam, and these are
sometimes called steam power stations. Not all thermal energy can be transformed into
mechanical power, according to the second law of thermodynamics. Therefore, there is
always heat lost to the environment. If this loss is employed as useful heat, for industrial
processes or district heating, the power plant is referred to as a cogeneration power
plant or CHP (combined heat-and-power) plant. In countries where district heating is
common, there are dedicated heat plants called heat-only boiler stations. An important
class of power stations in the Middle East uses by-product heat for the desalination of
A substation is a part of an electrical generation, transmission, and distribution system.
Substations transform voltage from high to low, or the reverse, or perform any of several other
important functions. Between the generating station and consumer, electric power may flow
through several substations at different voltage levels.
Substations may be owned and operated by an electrical utility, or may be owned by a large
industrial or commercial customer. Generally substations are unattended, relying on SCADA
(supervisory control and data acquisition) for remote supervision and control.
A substation has a metallic fence; it must be properly grounded to protect people from high
voltages that may occur during a fault in the network. Earth faults at a substation can cause a
ground potential rise. Currents flowing in the Earth's surface during a fault can cause metal
objects to have a significantly different voltage than the ground under a person's feet
Transmission Substation: A transmission substation connects two or more
transmission lines. The simplest case is where all transmission lines have the same
voltage. In such cases, the substation contains high-voltage switches that allow lines to
be connected or isolated for fault clearance or maintenance. A transmission station may
have transformers to convert between two transmission voltages, voltage
control/power factor correction devices such as capacitors, reactors and equipment
such as phase shifting transformers to control power flow between two adjacent power
Distribution Substation: Distribution substation transfers power from the
transmission system to the distribution system of an area. It is uneconomical to directly
connect electricity consumers to the main transmission network, unless they use large
amounts of power, so the distribution station reduces voltage to a level suitable for local
A 50 Hz electrical substation in Melbourne. This is showing three of the five 220 kV/66 kV
transformers, each with a capacity of 150 MVA. This substation is constructed using steel lattice
structures to support strain bus wires and apparatus
Transformers works over the principle of magnetic induction. There are two types of winding
namely primary and secondary. When a current is supplied to the primary winding a magnetic
flux is generated in the coil and by the law of magnetic induction and continuous change in
magnetic flux, a voltage is induced at the secondary coil which is used as the output.
The number of turns of the coil usually contributes by increasing or decreasing the output
voltage. This is known as:
* Step up transformer: where voltage is increased at the output terminal.
* Step down transformer: that reduces the voltage at the output terminal.
Transformers range in size from thumbnail-sized units hidden inside microphones to units
weighing hundreds of tons interconnecting the power grid. A wide range of transformer designs
are used in electronic and electric power applications. Transformers are essential for the
transmission, distribution, and utilization of electrical energy.
Despite the novel institutional arrangements and network designs of the electrical grid, its
power delivery infrastructures suffer aging across the developed world. Four contributing
factors to the current state of the electric grid and its consequences include:
1. Aging power equipment – older equipment have higher failure rates, leading
to customer interruption rates affecting the economy and society; also, older assets and
facilities lead to higher inspection maintenance costs and
further repair/restoration costs.
2. Obsolete system layout – older areas require serious additional substation
sites and rights-of-way that cannot be obtained in current area and are forced to use
existing, insufficient facilities.
3. Outdated engineering – traditional tools for power delivery planning and engineering
are ineffective in addressing current problems of aged equipment, obsolete system
layouts, and modern deregulated loading levels
4. Old cultural value – planning, engineering, operating of system using concepts and
procedures that worked in vertically integrated industry impair the problem under a
deregulated industry.
With everything interconnected, and open competition occurring in a free market economy, it
starts to make sense to allow and even encourage distributed generation (DG). Smaller
generators, usually not owned by the utility, can be brought on-line to help supply the need for
power. The smaller generation facility might be a home-owner with excess power from their
solar panel or wind turbine. It might be a small office with a diesel generator.
Furthermore, numerous efforts are underway to develop a "smart grid". In the U.S, the Energy
Policy Act of 2005 and Title XIII of the Energy Independence and Security Act of 2007 are
providing funding to encourage smart grid development. The hope is to enable utilities to
better predict their needs excess power from their solar panel or wind turbine. It might be a
small office with a diesel generator. Funds have also been allocated to develop more strong
energy control technologies. Various planned and proposed systems to dramatically increase
transmission capacity are known as super, or mega grids.
Recently, U.K’s National Grid, the largest private electric utility in the world, bought New
England’s electric system for $3.2 billion. Also, Scottish Power purchased Pacific Energy for
$12.8 billion. Domestically, local electric and gas firms begin to merge operations as they see
advantage of joint affiliation especially with the reduced cost of joint-metering. Technological
advances will take place in the competitive wholesale electric markets such examples already
being utilized include fuel cells used in space flight, aeroderivative gas turbines used in jet
aircrafts, solar engineering and photovoltaic systems, off-shore wind farms.
The electrical grid is expected to evolve to a new grid model--smart grid, an enhancement of
the 20th century electrical grid. The traditional electrical grids are generally used to carry power
from a few central generators to a large number of users or customers. In contrast, the new
emerging smart grid uses two-way flows of electricity and information to create an automated
and distributed advanced energy delivery network. Many research projects have been
conducted to explore the concept of smart grid. According to a newest survey on smart grid,
the research is mainly focused on three systems in smart grid- the infrastructure system, the
management system, and the protection system.
The infrastructure system is the energy, information, and communication infrastructure
underlying of the smart grid that supports
1) advanced electricity generation, delivery, and consumption;
2) advanced information metering, monitoring, and management. In the transition from
the conventional power grid to smart grid, we will replace a physical infrastructure with
a digital one.
The management system is the subsystem in smart grid that provides advanced
management and control services.
The protection system is the subsystem in smart grid that provides advanced grid
reliability analysis, failure protection, and security and privacy protection services.

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