Power Different Essential

50kVA PMTx Substation Transformer

Name: 50kVA Pole Mounted Substation Transformer
Rating: 50kVA
Cooling: Oil Cooled
Application: Commercial, Heavy Residential, Farm hold.
This type of transformer is mainly used for Step-Down purposes of voltages in the range of
11kV~415/240V.

Effects of Excess Current on the human body

Below 1 milli amperes (<1mA)
Generally not perceptible
1 milliamperes (1mA)
Faint tingle.
5 milliamperes (5mA)
Slight shock felt. Not painful but disturbing. Average individual can let go. Strong involuntary reactions can
lead to other injuries.
6-5 milliamperes (6-5mA)
Painful shock, loss of muscular control. The freezing current or "let-go" range. Individual cannot let go, but
can be thrown away from the circuit if exterior muscles are exited by the current.

Dangers of Electric Shock
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The severity of injury from electrical shock depends on the amount of electrical current and the length of
time the current passes through the body. For example, 1/10 of an ampere (amp) of electricity going
through the body for just 2 seconds is enough to cause death. The amount of internal current a person
can withstand and still be able to control the muscles of the arm and hand can be less than 10
milliamperes (milliamps or mA). Currents above 10 mA can paralyze or “freeze” muscles. When this
“freezing” happens, a person is no longer able to release a tool, wire, or other object. In fact, the
electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For
this reason, hand-held tools that give a shock can be very dangerous. If you can’t let go of the tool,
current continues through your body for a longer time, which can lead to respiratory paralysis (the
muscles that control breathing cannot move). You stop breathing for a period of time. People have
stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30
mA of current to cause respiratory paralysis.
Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition
will cause death within a few minutes unless a special device called a defibrillator is used to save the
victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned
with currents greater than 5 amps.

Longer exposure times increase the danger to the shock victim. For example, a current of 100 mA applied
for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds).
The muscle structure of the person also makes a difference. People with less muscle tissue are typically
affected at lower current levels. Even low voltages can be extremely dangerous because the degree of
injury depends not only on the amount of current but also on the length of time the body is in contact with
the circuit.
Sometimes high voltages lead to additional injuries. High voltages can cause violent muscular
contractions. You may lose your balance and fall, which can cause injury or even death if you fall into
machinery that can crush you. High voltages can also cause severe burns At 600 volts, the current
through the body may be as great as 4 amps, causing damage to internal organs such as the heart. High
voltages also produce burns. In addition, internal blood vessels may clot. Nerves in the area of the
contact point may be damaged. Muscle contractions may cause bone fractures from either the contractions themselves or from falls. A domestic socket will produce a maximum lethal current of 13A.

A severe shock can cause much more damage to the body than is visible. A person may suffer internal
bleeding and destruction of tissues, nerves, and muscles. Sometimes the hidden injuries caused by
electrical shock result in a delayed death. Shock is often only the beginning of a chain of events. Even if
the electrical current is too small to cause injury, your reaction to the shock may cause you to fall,
resulting in bruises, broken bones, or even death.
The length of time of the shock greatly affects the amount of injury. If the shock is short in duration, it may
only be painful. A longer hock (lasting a few seconds) could be fatal if the level of current is high enough
to cause the heart to go into ventricular fibrillation. This is not much current when you realize that a small
power drill uses 30 times as much current as what will kill. At relatively high currents, death is certain if the
shock is long enough. However, if the shock is short and the heart has not been damaged, a normal
heartbeat may resume if contact with the electrical current is eliminated. (This type of recovery is rare.)

Power System Network
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A detailed explanation of the conversion and distribution of electric energy from the power station to
consumer units.This post describes how electric energy moves from the power generating station through
conductors of various sizes to consumers premises.To minimize losses and for economical reasons,
electrical energy has to be converted into different magnitudes during transmission and distribution until
the consumer load.

POWER STATION

In most countries, electrical energy is generated at11kV, 33kV. It is generated by 3phase alternators in
parrarell. The electrical energy produced at the power station is Alternating Current (AC). AC is preferred
for transmission because it can be stepped up and down and with ease and efficiency. With AC, the
maintenance of substations is easier and cheaper as compared to DC. With the help of a step-up
transformer, electric current is stepped up to 132kV, 220kV and 400kV. Power is stepped up for
transmission so as to reduce losses during transmission and saving conductor material. High
voltage transmission lines are used to transmit this heavy current from the generating station to
transmission substation.

Power Generation Statistics:
India-11kV, 33kV
Kenya-11kV, 33kV
Tanzania-11kV

PRIMARY DISTRIBUTION SUBSTATION
The high voltage line terminates at a distribution substation. The substation receives voltage at 400kV,
220kV, 132kV or 66kV with the help of large 3phase step-down transformers. The substation is capable of
transmitting 6.6kV,11kV, 33kV and 66kV through different feeders depending on the target load. The
common 11kV line runs along important roads of the city. Large consumers being fed by 33 and 11kV
have their own substations for stepping down this voltage.

SECONDARY DISTRIBUTION SUBSTATION

These are the most common facilities in the electric power system. They provide distribution circuits that
directly supply most electric consumers. The pole mounted transformers are of this category. They
receive voltage of up to 11kV or 33kV and step it down to 415/240V (Kenya). As opposed to primary
distribution substations, the secondary ones do not have complicated equipment since they handle a
smaller amount of current. They are located near neighborhoods and are likely to be encountered by the
customers.
CONSUMER INTAKE

Depending on the type of load of the consumer, Single phase/3phase will be supplied from the distribution
line by connecting appropriately. Single phase shall be supplied to small consumers at 240V while 3phase
shall be supplied to large industrial consumers at 415V. At the consumer intake, the power supply
company provides the Energy meter depending on the tariff
selected.

CONSUMER CONTROL UNIT
The CCU is the point where the power is distributed throughout the consumer’s premises via fuses,
conductors and circuit breakers. This however is not supplied by the power distribution company. Current
in the premises is controlled at this point which has a single gang isolator switch to isolate the entire
premise.

Extra High Voltage Systems - 400kV Lines

Nominal Voltage
400kV
Cicuits per phase
1
Sub-conductors per phase
2
Span
400m
Conductor Name and Size
Moose,54/3.53mm Alluminium 7/3.53mm Steel
Sub-conductor Diameter
3.177cm
Bundle Configuration
Horizontal
Bundle Spacing
450mm
Interphase Spacing
11m
Condutor Configuration
Horizontal
Resistance per phase per km at 20degrees
0.0274Ohm
Inductive Reactance per phase per km
0.3321Ohm
Shunt Admittance per phase per km
3.2983*10-6
Surge Impedance
282Ohm
Surge Impedance Loading
505MW
Current Carying capacity at 40degrees ambient temperature 900A
Ground Wire
2Number,7/3.66mm Galvanised Steel
Ground wire height at tower
30.4m
Tower height
30.4m
Conductor Height at tower
20.75m
Conductor sag at 0degrees
8.39m
Ground wire sag at 0degrees
6.654m
Shielding angle
10degrees
Suspension string
23dics,225*145mm
Impulse Flashover voltage
1550kV
Examples:Sultanpur-Lucknow Line, Obra-kanput Line, Kanpur-Maradnagar Line.

The Aswan High Dam - Egypt
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Some brief statistics…
Official Name: Aswan High Dam
Length
: 3830 m

Height
: 111 m
Width (at base):980 m base, 40 m crest
Maintained by : Muaykensan
Reservoir information
Creates : Lake Nasser
Capacity : 111 km3
Power Generation Information
Turbines : 12
Installed capacity: 2.1GW
Introduction
Designed and built by the USSR's, Zuk Hydroproject Institute, which is a state organization that designed
the country's river-control schema, including 170 hydro-electric power stations, the Aswan Dam is Africa’s
tallest dam standing at a massive 1542 feet from the river bottom to a 131 ft crest, which is 11,810 feet
long. The dam holds back 1.99 trillion cubic yards of water, which creates the reservoir of 6 miles wide
and 310 miles long.
Construction
The earliest attempt of building a dam in Aswan dates back to the 1000s, when the Iraqi polymath and
engineer Ibn al-Haytham (known as Alhazen in the West) was summoned to Egypt by the Fatimid Caliph,
Al-Hakim bi-Amr Allah, to regulate the flooding of the Nile, a task requiring an early attempt at an Aswan
Dam.[1] After his field work made him aware of the impracticality of this scheme,[2] and fearing the
caliph's anger, he feigned madness. He was kept under house arrest from 1011 until al-Hakim's death in
1021, during which time he wrote his influential Book of Optics.
The Aswan High Dam was constructed in 1954 when the actual planning begun. In 1958, the Soviet
Union stepped in and funded the dam project. The Soviets also provided technicians and heavy
machinery. The enormous rock and clay dam was designed by the Soviet Hydroproject Institute along
with some Egyptian engineers. 25 thousands Egyptian engineers and workers formed the backbone of
the workforce required to complete this tremendous project which deeply changed many aspects in
Egypt.
Construction began in 1960. The High Dam, as-Sad al-'Aali, an embankment dam, was completed on 21
July 1970. It took 10 years to build with the first stage completed by 1964. The reservoir began filling in
1964 while the dam was still under construction and first reached capacity in 1976. In the late 1950's the
reservoir raised concern with archaeologists because major historical sites were about to be under water.
A rescue operation began in 1960 under UNESCO. Sites were to be surveyed and excavated and 24
major monuments were moved to safer locations or granted to countries that helped with the works (such
as the Debod temple in Madrid and the Temple of Dendur in New York).On the Egyptian side, the project
was led by Osman Ahmed Osman's Arab Contractors. The relatively young Osman underbid his only
competitor by one-half.

Construction Statistics:
At maximum, 11,000 cubic metres of water can pass through the dam every second. There are further
emergency spillways for an extra 5000 cubic metres per second and the Toshka Canal links the reservoir
to the Toshka Depression. The reservoir, named Lake Nasser, is 550 km long and 35 km at it’s widest with
a surface area of 5,250 square kilometres. It holds 111 cubic kilometres of water.
The dam rises 1542 feet from the river bottom to a 131 ft crest, which is 11,810 feet long.
The dam holds back 1.99 trillion cubic yards of water, which creates the reservoir of 6 miles wide and 310
miles long.
The largest cut-off in alluvial grouting soils and has the deepest cut-off of any dam, equal to 836 feet deep
and seals an area of 600,000 square feet.
The largest cut-off in alluvial grouting soils and has the deepest cut-off of any dam, equal to 836 feet deep
and seals an area of 600,000 square feet.
Vibration consolidation was used to compact the earth fill, creating the body of the dam.
28.6 Million Cubic Yards of Rock was used
20 Million Cubic Yards of Sand was used
4 Million Cubic Yards of Clay was used
55 Million Cubic Yards of Material was used.

Effects of the Dam
From an industrial and governmental perspective, both dams were successes in their original goals (to
control flooding, prevent drought, and supply hydroelectric power). From an environmental and
humanitarian perspective, these dams altered ecosystems and displaced native peoples that had lived in
harmony for literally tens of thousands of years. As with any major project, there is more than one side to

the story and humans continue to learn to predict the outcomes of their actions and the effects these new
conditions create.

Ngong Wind Power - Kenya
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Installed Capacity: 5.1 Mega Watts
Commisioning Year: 2009
Wind Turbines: 6
Output of each turbine: 850kW
Model: Vestas V52
Main Contractor TPF-Econoler SA (Belgium)
Location:Ngong Hills, 22km SW of capital, Nairobi - Kenya.
Standing tall at a height of 50m from the ground, the wind turbines rotate at the winds pace in a bid to
generate Kenya's source of Wind Power.The Ngong Wind Power Project which was commissioned in
August 2009, is Kenya's largest Wind Power Station but will come second once the Lake Turkana Wind
Power Project (LTWP) is completed.
The 6 Turbines, each with a maximum output of 850kW produce a total of 5.1MW of clean energy into the
grid.For the Vestas V52 Model turbines, KenGen executed a contract for the implementation of Ngong
Hills Wind Power project with TPF-Econoler SA (TPFE) of Belgium on 29th October 2007.
Operation
The turbines operate with the basic principle of mechanical to electrical conversion of energy. Each wind
turbine rotates a shaft which is connected to the generator at the top of the structure.The turbines start
operating when the wind speed reaches 4m/s and stops rotating at 25m/s referred to as the cut out
speed. The cutting out is to avoid mechanical failure due to strong forces at high wind speeds. Current
produced here is of AC (Alternating Current).The current produced is sent down via large cables of
correct rating to minimize losses.(P=Isq.R). Below the structure is the switchgear and control gear before
it is coupled with other turbines then to the grid.

The turbine blades are 26m long with a total diameter of 52m The blades were set in groups of three for
each turbine taking into account the static and dynamic balance required to avoid stress and vibrations
when in motion.The turbines which were installed were the size that could be transported on our
infrastructure. If we had larger roads we could have received larger structures=more power.
From there a precipitous dirt track wiggles its way up to the top. Quite simply bigger turbines on bigger
trucks could not have made the journey.The limiting factor is our infrastructure
Future Plans
By November 2012 Kengen seeks to increase the project output capacity to25.4MWwhich will see the
installation of more turbines as you head up the hill.

Corona
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Have you ever wondered why high voltage power lines buzz (zszszs
sound)? Its because they are producing corona which is interacting with the surrounding air.
Corona is the process by which current, perhaps sustained, develops from an electrode with a high

potential in a neutral fluid, usually air, by ionizing that fluid so as to create plasma around the electrode.
The ions generated eventually pass charge to nearby areas of lower potential, or recombine to form
neutral gas molecules. Plasma is a fourth state of matter (after solid, liquid, and gas). It is like a gas or
liquid, but molecules are separated into atoms, and the outer electrons are stripped off and are freed into
the plasma. In comparison, the sun is essentially a big ball of very hot plasma.
It is also the flow of electrical energy from a high voltage conductor to the surrounding air. This effect only
becomes significant for potentials higher than 1000V (1kV).It is characterized by a faint glow, a crackling
noise and conversion of atmospheric oxygen to ozone. The audible buzz sound becomes louder is there
is increased moisture & pollutants in the air.
Causes of Corona
Corona is causes by the following reasons:
The natural electric field caused by the flow of electrons in the conductor. Interaction with surrounding air.
Poor or no insulation is not a major cause but increases corona.
The use of D.C (Direct Current) for transmission.(Reason why most transmission is done in form of AC)
Effects of Corona
1.
Line Loss - Loss of energy because some energy is used up to cause vibration of the air
particles.
2.
Long term exposure to these radiations may not be good to health (yet to be proven).
3.
Audible Noise
4.
Electromagnetic Interference to telecommunication systems
5.
Ozone Gas production
6.
Damage to insulation of conductor.
Minimizing Corona Effects

Installing corona rings at the end of transmission lines.A corona ring,
also called anti-corona ring, is a toroid of (typically) conductive material located in the vicinity of a terminal
of a high voltage device. It is electrically insulated. Stacks of more spaced rings are often used. The role
of the corona ring is to distribute the electric field gradient and lower its maximum values below the
corona threshold, preventing the corona discharge.

Question & Answer about Corona
1. What voltage does arcing start at?
Potentially as low as 5 volts if there is follow-on current, such as electric arc welding.
2. What voltage does arcing extinguish at?
It depends, but most of the time about 50% of the voltage it started at. Remember this when
troubleshooting a radio interference problem, if the radio noise is there, turn the line off, if it goes away,

turn the line on again, if the noise is not present then it is probably arcing caused by capacitor switching
or transients, if the noise is there when the line is turned back on, then it is probably arcing and this can
be visible a mile away with a daytime corona camera.
3. What is a good readily available RFI/TVI noise detector?
The AM radio in your car or truck tuned where there is no radio station and adjusts the volume for
comfort, then drive into the radio interference complaint area and listen for the loudest pole. Some noises
can be outside the radio reception and will require other detectors.
4. What can cause RFI/TVI?
Electrical arcing, micro-arcing, and for a utility items such as loose tie wires at insulators, loose washers
or hardware, spark gaps between pieces sometimes rattled by heavy vehicle traffic, in industry or the
home causes can range from TV sets, microwaves, transformers, electric motors, vehicles spark plug
wiring, over the road diesel trucks with inverters, etc. places where an arc can flash-over momentarily but
be limited in current flow so it doesn't result in a continuous flash-over.
5. What is electrical corona?
Corona is the ionization of the nitrogen in the air, caused by an intense electrical field. Electrical corona
can be distinguished from arcing in that corona starts and stops at essentially the same voltage and is
invisible during the day and requires darkness to see at night. Arcing starts at a voltage and stops at a
voltage about 50% lower and is visible to the naked eye day or night if the gap is large enough (about 5/8"
at 3500 volts).
6. What are the indications of electrical corona?
A sizzling audible sound, ozone, nitric acid (in the presence of moisture in the air) that accumulates as a
white or dirty powder, light (strongest emission in ultraviolet and weaker into visible and near infrared) that
can be seen with the naked eye in darkness, ultraviolet cameras, and daylight corona cameras using the
solar-blind wavelengths on earth created by the shielding ozone layer surrounding the earth.
7. What damage does corona do?
The accumulation of the nitric acid and micro-arcing within it create carbon tracks across insulating
materials. Corona can also contribute to the chemical soup destruction of insulating cements on insulators
resulting in internal flash-overs. The corona is the only indication. Defects in insulating materials that
create an intense electrical field can over time result in corona that creates punctures, carbon tracks and
obvious discoloration of NCI insulators.
8. How long does corona require to create visible damage?
In a specific substation the corona ring was mistakenly installed backwards on a temporary 500kV NCI
insulator, at the end of two years the NCI insulator was replaced because 1/3 of the insulator was white
and the remaining 2/3 was grey.
9. What voltage are corona rings typically installed at?
It varies depending upon the configuration of the insulators and the type of insulator, NCI normally start at
160kV, pin and cap can vary starting at 220kV or 345kV depending upon your engineering tolerances and
insulators in the strings.
10. What causes flash-over?
Flash-over causes are not always easily explained, can be cumulative or stepping stone like, and usually
result in an outage and destruction. The first flash-over components are available voltage and the
configuration of the energized parts, corona may be present in many areas where the flash-over occurs,
flash-over can be excited by stepping stone defects in the insulating path.
11. How to test insulators?
Always remember to practice safety procedures for the flash-over voltage distance and use a sturdy
enclosure to contain an insulator that may shatter, due to steam build-up from moisture in a cavity, arcing
produces intense heat, an AM radio is a good RFI/arcing detection device, a bucket truck AC dielectric
test set (130KV) is a good test set for most pin and cap type insulators. A recent article said the DC
voltage required to "search out defects can be 1.9 times the AC voltage.
Insulators have a normal operating voltage and a flash-over voltage. Insulators can have internal flashovers that are/are not present at normal operating voltage. If the RFI is present, de-energize the insulator
(line) and if the RFI goes away, suspect the insulator (line). Then there can be insulators that have arcing
start when capacitor or other transients happen, stop when the line is de-energized or dropped below
50% of arc ignition voltage. Using a meg-ohm-meter can eliminate defective insulators that will
immediately arc-over tripping the test set current overload.
12. Conductor corona is caused by?

Corona on a conductor can be due to conductor configuration (design) such as diameter too small for the
applied voltage will have corona year-around and extreme losses during wet weather, the opposite occurs
during dry weather as the corona produces nitric acid which accumulates and destroys the steel
reinforcing cable (ACSR) resulting in the line dropping. Road salts and contaminants can also contribute
to starting this deterioration.
13. Why should I care?
Insulating materials that are failing can cause flash-overs and outages.
14. Why will my boss (and his boss) care?
Any outage costs repair time and lack of customer service, in this age we are all somebodys customer.
15. How does this cost our company?
Lost opportunity revenue, you can't sell electricity or make products if you don't have power. An
inexpensive part (cotter pin devoured by corona acid) can fail and cost a transformer by the time the
sparks quit flying. Customers with continuous process applications, critical care facilities, computing
systems typically have uninterruptible power and back-up generating capacity for part of there load for a
limited time.
16. How does this affect the reliability of our electrical system?
Corona is a symptom, it may be present for years before the component finally fails. Corona can be an
indication or the catalyst of the chemical soup that permeates insulator bonding cements preparing them
for internal flash-over. How can you detect this, ask me.
17. What tools are available to identify the presence of corona?
Corona produces sound, nitric acid (in the presence of moisture), ozone, and ultraviolet light. No RFI/TVI
here as this is a chemical reaction.
18. Are there presentations of the tools we need to understand to select the right corona or arcing
detection tool?
Yes, please contact me for a Corona CD with presentations, articles, and learn how we locate corona and
prevent electrical outages.
19. Is there training available for our staff in understanding corona interpretation and the
operation and use of the corona tools?
Yes, please see the Corona Technology Course and also the Corona Sleuth Presentation and ask me.
http://www.corona-technology-course.com
20. What is flash-over and arcing?
Flash-over is an instantaneous event where the voltage exceeds the breakdown potential of the air but
does not have the current available to sustain an arc, an arc can have the grid fault current behind it and
sustain until the voltage decreases below 50% or until a protective device opens. Flash-over can also
occur due to induced voltages in unbonded (loose bolts, washers, etc) power pole or substation
hardware, this can create RFI/TVI or radio/tv interference. Arcing can begin at 5 volts on a printed circuit
board or as the insulation increases it may require 80kVAC to create flash-over on a good cap and pin
insulator.
21. What are causes of insulator failure?
Electrical field intensity producing corona on contaminated areas, water droplets, icicles, corona rings, ...
This corona activity then contributes nitric acid to form a chemical soup to change the bonding cements
and to create carbon tracks, along with ozone and ultraviolet light to change the properties of NCI
insulator coverings. Other detrimental effects include water on the surface or sub-surface freezing and
expanding when thawing, as a liquid penetrating into a material and then a sudden temperature change
causes change of state to a gas and rapid expansion causing fracture or rupture of the material.

Kengen to shut down Emergency Power Generators
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The Kenya Electricity Generating Company, KenGen: Kenya's largest power producer is ready to switch
off Emergency Power Generators. These power generators were commissioned last year (2009) during
the period of acute shortage in power caused by low rainfall and low water levels in the hydroelectric
dams.
The Emergency Power Generators which produce 150MWinto the grid, produce power from Diesel fuel
resulting in the high electricity costs for Kenyans. The Power Relief cost the government 1.7Billion Ksh
and have been running since the commissioning.
The expected switch off of these fuel guzzlers will take place on 6th January 2010.This will mean less
power bills in the coming future as the government calls investors to explore the rich energy potential of
Kenya. On the other hand, The Kenya Power & Lighting Company, KPLC - The Largest distributor of
power, said consumers have been pointing a finger on them blaming them of huge power bills. KPLC has
reassured its customers that they have to charge a higher Fuel Levy because of the Emergency Power
generators.
A recent survey of the power in Kenya shows that the countries over-reliance of Hydro Power has seen
massive shortage of power once the rains falls. It is because of this that Ken Gen has embarked of an
expansion of its Geothermal Power at Olkaria, Naivasha.

Stadium Power Supplies - FIFA World Cup 2010
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Given the national and international exposure that each stadium in the FIFA World Cup 2010 receives, it
is imperative that all efforts are made to ensure that electrical power supply in the venues is as reliable as
possible. In this post according to “22nd AMEU Technical Convention110 AMEU Proceedings 2009
Stadium electricity supplies – an assessment of the specification and readiness” document I have outlined
the various power aspects involved in Stadium Power Supplies.

The stadia and surrounding areas are fundamentally broken down into three
Main focus areas include:
1. Domestic/stadium power (stadium itself)
2. Technical Power (Media & Broadcasting)
3. Overlay or precinct (area immediately surround the stadium including ticketing offices, hospitality,
Accreditation etc)
Domestic/Stadium power
The agreements signed by the host cities and FIFA in the delivery of sufficient back-up power grids to
deal with any power failure at the stadium and elsewhere in the host city which may arise during a match,
and that appropriate power management systems are in place.” FIFA 2007 Specification – host city
agreement
Below is what is expected with regard to this statement:
Pitch Lighting: “The primary goal of the event lighting system is to illuminate the event to digital video
quality for the media without creating nuisance glare for the players/officials and adding spill light/glare to
the spectators and surrounding environment. Permanent lighting, temporary lighting and a combination of
both systems should be considered.” FIFA Football Stadiums Technical recommendations and
requirements, 4th Edition
- Host city is responsible for pitch lighting.
- Lighting intensity of 2400 Lux (fixed camera lighting) with 1800 Lux at pitch level (field camera) is
required at all times.
- Available and functioning 100% during a match.
- Zero switch time tolerance. i.e. switching between electrical supplies must have no impact on the pitch
lighting.
- Recommendation to have some sort of uninterruptable power supply (UPS) to ensure that any anomaly
(Dips, surges etc) on the network (grid or generator) has no influence on the pitch lighting. Having a UPS
would also ensure that the potential impact on pitch lighting during switching between electrical supplies
will be mitigated. AMEU Proceedings 2009 111
- Generators or alternate power supply capable of sustaining the pitch lighting for a minimum of three

hours.
- Maintenance and refueling are the responsibility of the host city.
- Configuration of the power supply is at the discretion of the host city but must have a minimum n-1
redundancy.
Stadium building power: Stadium building power is the required supply within the stadium to power
appliances, facilities and lighting within the stadium i.e. general stand lighting, administration offices and
suites.
- Backup power requirement in the event of a power failure is limited to that of the Occupational Health
and Safety Act (OHSACT)
- This power excludes any broadcast or media provisioning.
- Configuration of the MV power supply is at the discretion of the host city and is recommended to have
minimum n-1 redundancy.
Technical power
This is power for the broadcasting and television requirements.
No host city involvement. This is the responsibility of the LOC.
No grid supply. Islanded from the grid power supply. Supply is provided via diesel generators supplied by
the LOC. Covers all broadcasting mediums.
Total of three 500 kVA generators each capable of taking the full load. Two generators run in parallel with
the third being a backup. A fourth generator will be required for the venue hosting the final game.
Zero supply switching tolerance, this means no time interval in the changing from diesel power to auxiliary
power in case of a problem with generators.
Overlay/Precinct power
This is Area immediately surrounding the stadium including ticketing offices, hospitality, accreditation etc.
Host city is responsible to supply a medium voltage (11 kV) point/s of supply. For 2010 there may be as
many as four required per stadium and the number and location of these bulk supply points will be
stadium dependent.
Other Stadium loads
The following other stadium loads require an automated switched firm supply (to either an independent
grid supply or local backup generation):
1. Emergency lighting (Stadium and parking)
2. First aid/medical facility
3. Broadcast Links (Typically broadcasters provide their own generation and make use of stadium supply
as a backup)
4. Commentary box (UPS)
5. Switchboard (UPS)
6. Team change rooms
7. Other stadium lights
8. Food halls
9. Fridges
Preparation
The 2010 FWC was the event of events, a once in a life time experience, and the number of
role players and stakeholders who were involved in the preparation and execution bear witness to this.
The information found in the points below is relevant and applicable to the stadia preparation and other
2010 critical loads.
Generation and transmission
The mitigation of risks for these components is primarily an Eskom responsibility and includes:
1. Ensuring adequate primary energy supply prior to the event.
2. The management of plans for the taking of generation and transmission plant out of service for planned
maintenance or refueling (Koeberg) in order that the risk to the tournament is minimized.
3. The identification and assessment of Infrastructure providing supply to municipal distributor areas,
which could directly or indirectly influence the supply to any of the stadiums, for condition and

maintenance or refurbishment plans.
4. Detailed emergency planning and simulation of these plans prior to the event.
5. Plans for obtaining and storing of strategic spares, as well as logistic constraints such as
communications and transport are in place.
6. Inspection of networks will take place earlier than normal practice for those networks identified as
critical for reliability and quality of supply.
Distribution
The establishment of regional task teams (RTT) in all the host cities has enabled the preparation to be
tracked and understood. The suggested actions that are being carried out (many have been completed)
by the relevant host cities include:
1. Identify and assess the condition of the electrical infrastructure that could directly or indirectly influence
the supply to the stadium(s), training venues and key loads in their area of responsibility.
2. Replacement, refurbishment or maintenance of these networks to be scheduled to be completed well
before the commencement of the tournament.
3. Evaluate the requirement and availability of strategic spares for their network.
4. Assess loads connected to load shedding relays and revise existing plans to ensure that there is no
impact on identified tournament critical loads should the need for load shedding arise.
5. Arrange networks so that no abnormal conditions are maintained during the period of the tournament.
6. Prepare contingency plans for supplies to the critical loads and ensure all control and operations
personnel are thoroughly familiar with switching requirements.
7. Plan leave and standby rosters well in advance to ensure the availability of an adequate level of
competent staff.
8. Optimize security measures for the protection of critical infrastructure. Stadia Each of the host cities
have achieved the requirements for stadium supplies differently considering legacy requirements and
historical infrastructure and layout.
Power Statistics
1. Ellis Park (Johannesburg) Primary power – generators – 2 x 700 kVA – 2 x 800 kVA – 1 x 500 kVA
Backup power – grid (n-1) – Prospect – Delta Uninterruptable power supply (UPS).
2. Free State Stadium (Bloemfontein) Primary power – generators – 2 x 1250 kVA 112 AMEU
Proceedings 2009 Backup power – grid (n-1) Configured to run parallel.

3. Royal Bafokeng Sports Palace (Rustenburg) Primary power – generators – 2 x 2200 kVA Backup
power – grid (n-1) Uninterruptable power supply (UPS).

4. Loftus Versveld (Pretoria) Primary power – generators – 8 x 300 kVA Backup power – grid (n-1)
Uninterruptable power supply (UPS) per light mast.

5. Green Point (Cape Town) Primary power – grid supply (n-1) Backup power two sources of power. 2 x 2
MVA fixed generator supply Supplemented by 4 x 500 kVA generators. Uninterruptable power supply
(UPS)

6. Moses Mabhida Stadium (Durban) Primary power – generators – 3 x 800 kVA Backup power – grid – 2
x 11kV sources from separate locations. There is currently no allowance made for any UPS supplies at
the Moses Mabhida Stadium, albeit that the consultants have made physical arrangements to incorporate
as such.

7. Soccer City (Johannesburg) Primary power – generators Backup power – grid (n-1) Uninterruptable
power supply (UPS).

8. Mbombela Stadium (Nelspruit) Primary power – generators Backup power – grid (n-1) Uninterruptable
power supply (UPS).

9. Peter Mokaba Stadium (Polokwane) Primary power – generators Backup power – grid (n-1)
Uninterruptable power supply (UPS).

10. Nelson Mandela Stadium (Port Elizabeth) Primary supply – grid supply (Mount R substation @ 66/22
kV) Backup power – gas turbine

There are rotary UPSs which are installed in each of the 4 stadium substations which will be dedicated for
pitch lighting and emergency supplies.

The Xiangjiaba - Shanghai ±800kV UHVDC Transmission
Line Project
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Recent developments in High Voltage transmission and distribution systems have shown a gradual
increase in DC transmission systems at very high voltage levels. High Voltage Direct Current (H.V D.C)
has become common in developed countries due to reduced costs at high voltages as compared to
Alternating Current (A.C) transmission. It is because of such reasons that the recently completed
Xiangjiaba-Shanghai 800kV UHVDC transmission line was built.

Project Details
Operating Voltage: ±800kV DC
No. of Poles: 2
Connection Point Xiangjiaba: Fulong Substation
Connection Point Shanghai: FengXiang Substation
Ownership: State Grid Corporation of China
Start of Project: December 2007
Commissioning Year: Pole 1 and Bi-pole 2010

Transmission Technology: UHVDC (Ultra High Voltage Direct Current)
Transmission Capacity: 6,400MW (6.4GW)
Length of Overhead DC Line: 2,071km
AC Voltage: 525kV (both ends)
Main Reason for Choosing HVDC: Long Distance and Low Losses
HVDC converter stations: Convert AC to DC and DC to AC
Design Supply and Installation: ABB
This new link is able to meet the electricity needs of about 24 Million people and sets a new benchmark in
terms of voltage levels and transmission capacity, superseding the 600kV Itaipu transmission line in
Brazil, also by ABB

DC Transmission and Distribution
In DC transmission technology the following terminologies are used:
<300kV: High Voltage (H.V)
300kV-765kV: Extra High Voltage (E.H.V)
>765kV: Ultra High Voltage (U.H.V)
DC technology is used for large transmission and distribution of power at high voltages because at such
large quantities, the systems are less expensive and suffer lower power losses. HVDC has found its place
due to economic reasons of transmission.
Generation of DC (Direct Current)
Generally there are two methods of producing DC power:
1. Standard DC Generators
2. Converting AC to DC Using: Motor Generator Sets
6phase Mercury Arc Rectifiers
Rotary Converters

Standard DC Generators
A standard DC Generator is an electrical machine that consists of a magnetic coil provided by permanent
or electromagnets, and a coil of wire of a significant number of turns rotating in the magnetic flux.
According to Faradays’ Law of Electromagnetism induction, a DC current shall be produced when the coil
is rotated.

Converting AC to DC
The conversion of AC to DC is nowadays used in parallel to AC for specific loads that use strict DC.
However this is done at a large scale in HV and EHV.
1. A motor GenSet is simply a motor driven by AC to provide mechanical power to a generator
producing DC.
2. A rotary converter is a type of electrical machine where a motor-generator machine shares a single
rotating armature and set of field coils.
3. 6phase mercury arc converters are solid state devices that are used for producing DC power to be
sued by railways and for electrolytic processes.
Transmission & Distribution
DC Power maybe fed and distributed either by:
2-Wire System
3-Wire System
2-Wire System
In this system, one wire is the Outgoing or Positive wire and the Outers is the Return or Negative wire.
The standard voltage between the conductors is 220V but this may depend in the project involved. This
system has much lower efficiency and economy as compared to the 3-wire system.
3-Wire System
This system provides 2 voltages to be available at the consumers end. The Middle/Neutral is earthed at
the generator end. It potential is midway between the outers. Motors requiring higher voltages are
connected across the Outers whereas lighting and heating circuits requiring less voltage are connected
between any of the Outers and Neutral.

Advantages of HVDC over HVAC Transmission
1. No inductance, capacitance, phase displacement and surge problems in DC
2. Due to the absence of inductance, the voltage drop in a HVDC line is less than A.C line for the same
load and sending voltage.
3. No skin effect in DC therefore entire cross section of the line conductor is utilized.
4. A DC line has less corona effect and reduced interference with communication circuits.
5. HVDC can used to connect remote generating plants to the distribution grid.
6. Facilitate power transmission between different countries that use AC at different operating voltages
or frequencies.
7. Synchronize AC produced by renewable energy sources.
Disadvantages of HVDC
1. High cost of transmission and conversion equipment
2. HVDC is less reliable and lower availability than AC systems
3. HVDC circuit breakers are difficult to build because some mechanism must be included in the circuit
breaker to force the current back to zero. Otherwise arcing and contact wear would be too great to allow
reliable arching.

4. Operating a HVDC requires many spare parts to be kept, often exclusively for one system since
HVDC systems are less standardized.

Costs of HVDC
Normally, manufactures such as Alstom, Siemens and ABBdo not state specific costs of information of a
particular project since this is a commercial matter between the manufacturer and client. Costs are wide
depending on the specifics of the project such as Power rating, Circuit Length, Overhead vs. Underwater
route, Land Costs and AC Network improvements required at terminal.
For an 8GW 40km link laid under the English Channel, an approximate Primary equipment costs for a
2000MW 500kV bipolar convectional HVDC link (excluding way-leaving, onshore-reinforcement works,
consenting, engineering, insurance etc) is as follows:
Converter Stations= £110Million
Subsea Cable + Installation =£1Million/km
THE XIANGJIABA - SHANGHAI ±800kV UHVDC TRANSMISSION PROJECTOwned by the State Grid
Corporation of China, the Xiangjiaba-Shanghai Project has the capacity to transmit up to 7,200MW
(7.2GW) of power from the Xiangjiaba Hydro plant in S.W China to Shanghai. This new link will meet the
electricity need if 24Million people and set a new record in terms of voltage levels and transmission
capacity, superseding the 600kV Itaipu transmission line in Brazil.
Transmission line losses on the new line are well under 7%. ABB, being the main technology supplier, is
responsible for the overall system design. The scope of delivery of equipment to Xiangjiaba included 28
High and Ultra High Voltage converter transformers. 10 of which were delivered from Sweden and the rest
manufactured with ABB components and technology in local partnership. Other products delivered
include: Thyristor Valves, DC and AC Switchyard equipment and the newly developedDCC800 HVDC
Control System.

“800kV UHVDC will play an important role in providing China with access to remote renewable energy, a
key focus are for us”, Says Zheng Bosen, Executive Vice President, SGCC. One thing to note is that, the
transmission line which went into commercial operation last month, was actually completed 30 Months
1year ahead of schedule. In response to this Zheng Bosen was very pleased to the good work done by
ABB.
Highlights of the Project
1. The new system voltage ±800kV is 33% higher than the voltage used for Itaipu ±600kV transmission

line.
2. The Power rating, 6,400MW (6.4GW) is more than double the power rating of the most powerful
transmission line in operation today.
3. Line losses shall be reduced to 7% compared with 10% if the line had been built with convectional
500kV DC transmissions.
4. The overhead line length 2,071km will be one of the longest overhead transmission line in the world,
surpassed only by the over 2,500km long Rio Madeira HVDC link currently under construction in brazil.
For quite some time the 1,700km long Inga-Shaba HVDC line in Congo-Brazil was the longest
transmission line.
An UHVDC link, 2,000 km long is 30% cheaper, partly because it reduced electricity loses by 30% as
compared with 500kV DC or 800kV AC technology.
Future Trends in UHVDC
1. India plans to build 5 UHVDC lines over the next 10years, each with a capacity of 6,000MW
(6
GW).
2. China is planning one line every year for the next decade, each with a capacity of 5000MW (5GW) or
6,400MW (6.4GW).
3. There are also plans to install 800kV UHVDC lines in Southern Africa in Brazil.

Power Factor #1
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What exactly is Power Factor?
Power Factor (i.e. Cosɸ) of a circuit can be defined as:
Cosɸ = the cosine of an angle between Voltage (V) and Current (I).
R/Z = Resistance/Impedance
VICosɸ/VI = True Power/Apparent Power

The value of power factor can never be greater than 1(Unity)

It is usual practice to attach the word ‘lagging’ or ‘leading’ with the numerical value of power factor to
signify whether the current lags or leads the voltage. Thus if a circuit has p.f. of 0.6 and the current lags
the voltage, we generally write p.f. as 0.6 lagging.
Power factor can also be expressed as a percentage i.e. 60% lagging.

Power Factor #2
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Power factor in Relation to Power

Power is consumed only in resistance since neither pure inductor nor the capacitor consumes any
power. The power consumed (True Power) in Inductor (L) and Capacitor (C) is zero. There is a circulating
power that moves from the source to the load back and forth and does not do any useful work in the
circuit. Current and voltage are in phase in a Resistance while they are 90 Degrees out of phase in (L)
and (C).When current is in phase with voltage it produces active or True Power while it produces Reactive
Power when 90 Degrees out of phase with voltage.

Power Triangle
Note:Due to formating limitations, all squared values shall be indicated by (squared)
OA(squared) + AB(squared) =OB(squared)
(Active Power)(squared)+(Reactive Power)(squared) = Apparent Power)(squared)
The lagging rective power is responsible for low power factor.The smaller the reactive power component,
the higher the power factor.
kVAR = kVISinø
kVAR = kVASinø
but Cosø =kW/kVA
therefore kVA = kW/Cosø
kVAR =kW/Cosø*Sinø
kVAR = kWtanø
For Leading currents, the power factor triangle becomes reverse biased and this provides a key factor in
power factor improvement.If a device taking leading currents or reactive power, a capacitor is connected
with this device in parrarell and the power factor is improved.Capacitors take in a leading power factor
and thus are used in power factor correction.
Example:
If a circuit draws a current of 10A at a voltage of 200V and its pf is 0.8 lagging, determine the Active,
Reactive and Apparent Power.
For apparent power;
P = IV
P=10*200
2000VA
For active power;
P = IVCosø
P = 10*2000*Cosø
P = 1600W

(Cosø =Power Factor=0.8)

For reactive power;
P = IVSinø
P = 10*200*Sinø
P = 1200VAR
From the above calculations we can see that the circuit receives an apparent power of 2000VA and it is
capable of converting only 1600W into useful active power. The reactive power is 1200VAR and it does
no useful work. In fact it is a liability on the source because it has to supply an additional current of ISinø.
Disadvantages of Low Power Factor.
1. Large kVA rating of equipment (switchgear, alternators, transformers)
We know that kVA =kW/Cosø
Therefore Cosø =kW/kVA
When ø is increasing, Cosø is decreasing and when ø is decreasing Cosø is increasing. It is from this
simple fact that we can conclude that when the power factor is decreasing the kVA is increasing, the
smaller the power factor the larger the kVA rating of the equipment.
2.Greater Conductor Size
To transmit and distribute a fixed amount of power at a constant voltage, the conductor will have to carry a

current at low power factor. This will necessitate the use of a greater conductor size.
3.Large Copper Losses.
The Large current at low power factor causes I2R Losses in all the elements of the supply system and
this results in poor efficiency.
4.Poor Voltage regulation.
The large current at a low lagging power factor causes greater voltage drop in alternators, transformers,
transmission lines and distributors. This result in increased voltage drop at the receiving end, thus
imparing the performance of the utilization devices. Extra equipment is required i.e. Voltage regulators.
Reduced handling capacity of a system.
Because of the reactive component of current, this prevents full utilization of the installed capacity.

Power Factor (In Detail) #3
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Related Posts
Power Factor #1
Power Factor #2
From our previous discussion we saw that Power Factor can be defined in 3 definitions. ie


The cosine of an angle between Voltage (V) and Current (I)



True Power / Apparent Power



Resistance / Impedance

Please note that in the above expressions, the value of Power Factor can never be greater than 1. A good
power factor is always 0.9 or 0.89
In this post we are going to look into detail the Power Factor of angle between Voltage(V) and Current (I)
The power factor PF is mathematically defined as the cosine of the phase angle between voltage and
current. True power is defined by the equation . The graphical representation produces a product of the
voltage and current. This product is represented as a sine wave, which is twice the frequency of the
voltage and current and represents the instantaneous power and its direction. If the power sine wave is

completely on the positive side of the axis, it shows that the power in the system is traveling only in one
direction, toward the load.
The area under this power sine wave curve represents the amount of energy delivered to the load. If the
power sine wave is shifted, the difference in area between the positive and the negative sides represents
the power delivered to the load. The negative side of the power sine wave represents the reflected power
from a reactive load.
A lagging power factor is one in which the current is lagging behind the voltage and is characteristic of an
inductive load.
A leading power factor is one in which the current is leading the voltage and is characteristic of a
capacitive load. If the phase angle were to be shifted to be greater than 90 degrees in either direction, the
load would effectively become the source.
Power Factor Correction
A power factor of one (1) or "unity power factor" is the goal of any electric utility company since if the
power factor is less than one (<1) , they have to supply more current to the user for a given amount of
power use. In so doing, they incur more line losses. They also must have larger capacity equipment in
place than would be otherwise necessary. As a result, an industrial facility will be charged a penalty if its
power factor is much different from 1.
Industrial facilities tend to have a "lagging power factor", where the current lags the voltage (like an
inductor). This is primarily the result of having a lot of electric induction motors - the windings of motors
act as inductors as seen by the power supply. Capacitors have the opposite effect and can compensate
for the inductive motor windings. Some industrial sites will have large banks of capacitors strictly for the
purpose of correcting the power factor back toward one to save on utility company charges.

Hydroelectric Power Station
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This is a generating station which utilizes the potential energy of water at a high
level for the generation of electrical energy. It uses the gravitational force of
falling or flowing water. They are located in hilly areas where dams can be built
and large water reservoirs can be obtained. Hydroelectricity is the most widely
used form of renewable energy. Worldwide an installed capacity of 77GWe
supplied a total of 2998TWe of hydroelectricity in 2006. This was approximately
20% of the world's electricity and accounted for about 88% of electricity from
renewable
sources...
Most hydroelectrity comes from the potential energy of dammed water driving a
water turbine coupled to a generator. Therefore the energy extracted from the
water much depends on the difference in height between the source and the
waters outflow. This height difference is called the head. To obtain a very high
head, water for a hydraulic turbine may be run through a large pipe called a
penstock.
While most of the power stations are built for public utility networks, there are
those dedicated to supply large electricity needed for aluminum electrolytic
plants and other industrial establishments. Examples include: In the Scottish
Highlands of United Kingdom, Kinlochleven and Lochaber were constructed
during the early years of the 20th century. In Suriname, the Brokopondo
Reservoir was constructed to provide electricity for the Alcoa aluminum
industry. New Zealand's Manapouri Power Station was constructed to supply
electricity to the aluminum smelter at Tiwai Point

GENERATION OF POWER AT A H.E.P STATION

The dam is constructed across a river or a lake
and water collects behind the dam to form a reservoir. A pressure tunnel is
taken off the reservoir and water is brought to the valve house at the start of the
penstock. The valve house contains the main sluce valve which controls the
water flow to the power house and automatic isolating valves which cuts off
supply of water when the penstock bursts. From the valve house water is taken
to the turbine through the penstocks. The turbine converts hydraulic energy into
mechanical energy. The surge tank protects the penstock from bursting in case
the turbine gates close due to electrical load being thrown off. When the gates
close, there is a sudden stopping water at the lower ends of the penstock. The
surge tank absorbs this pressure swing by increase in its level of water. The
water turbines are of 2 types namely: Impulse and Reaction turbines.

Advantages of Hydroelectric Power


Requires no fuel since it uses water as a source of energy.



Less or no greenhouse gas emissions in modern plants.



Can be used for many purposes i.e. Control floods, Irrigation.



Longer operational life i.e. 30years.

Disadvantages of Hydroelectric Power


Dam Failure Hazard - When the dam cannot hold the massive force of the held water it breaks
and sends water at speeds of 50kph downstream. Death, Instant Power failure and destruction of
infrastructure will follow. Dam failures have been some of the largest man-made disasters in history. Also,
good design and construction are not an adequate guarantee of safety. Dams are tempting industrial
targets for wartime attack, sabotage and terrorism. The Banqiao Dam failure in Southern China resulted
in the deaths of 171,000 people and left millions homeless. Also, the creation of a dam in a geologically
inappropriate location may cause disasters like the one of the Vajont Dam in Italy, where almost 2000
people died, in 1963.The November 2009 Brazil and Paraguay blackout dam failure ,14 GW of output
power was lost.


Population relocation - Another disadvantage of hydroelectric dams is the need to relocate the
people living where the reservoirs are planned. In February 2008, it was estimated that 40-80 million
people worldwide had been physically displaced as a direct result of dam construction. In many cases, no
amount of compensation can replace ancestral and cultural attachments to places that have spiritual
value to the displaced population. Additionally, historically and culturally important sites can be flooded
and lost. Such problems have arisen at the Three Gorges Dam project in China, the Clyde Dam in New
Zealand and the Ilisu Dam in Southeastern Turkey.


Low Shortage - Since they are fed by rivers and streams, a dip in the level of water in these
rivers results in reduced outputs of the power stations. In many countries which rely heavily on
Hydroelectric power i.e. Kenya, suffer a lot due to insufficient rainfall during drought periods.
LARGEST HYDROLELECTRIC POWER PLANTS.

The Three Gorges Dam complex on the Yangtze River in Hubei, China, has the
world's largest generating capacity and generates the most electricity in the
world. It includes 2 generating stations. They are the Three Gorges Dam
(22,500 MW when completed) and Gezhouba Dam (3,115 MW). As of 2009, the
total generating capacity of this complex is 21,515 MW. The whole project is
planned to be completed in 2011, when the total generating capacity will be
25,615 MW. In 2008, this complex generated 97.9 TWh of electricity.

"The Itaipu power plant on the Paraguay River
on the Brazil-Paraguay border currently produces second most hydroelectricity
in the world. With 20 generator units and 14,000 MW of installed capacity, in
2008 the Itaipu power plant reached a new historic record for electricity
production by generating 94.68 terawatt-hours (340,800 TJ).

Facts & Figures - Top 6 Power Producers
Three
Gorges
Dam
Country:
China
Date
of
completion:
2008/2011[1]
Total Output (GW): 18,300 (October 2008) 22,500 (when complete)
Area
Flooded:
632km2
Itaipu
Country:
Date
Total
Area

of

Guri
Country:
Date
Total
Area

of

Tucurui
Country:
Date
Total
Area

of

Grand
Date
Total
Area

Brazil/Paraguay
1984/1991/2003
14,000MW
1,350km2

completion:
Output:
Flooded:
(Simón

Bolívar)
Venezuela
1986
10,200MW
4,250km2

completion:
Output:
Flooded:

completion:
Output:
Flooded:

Brazil/Paraguay
1984
8,370MW
3,014km2

Coulee Country:
United
of
completion:
Output:
Flooded:
(No

Sayano
Shushenskaya
Country:
Date
of
Total
Area Flooded: 621km2

(17

august

completion:
Output:

2009

States
1942/1980
6,809MW
Data)
-

Stopped)
Russia
1985/1989
6,400MW

Which one is more dangerous, AC or DC?
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This question has been asked by many people who have experienced an
electric shock before.I recently received an electric shock from the
domestic household current of 10A.The feeling was ecstatic. Many will come
across large AC currents, but have you ever thought of DC Electrification?
This would sound weird because DC current available in domestic premises
is in the order of mA (milliamperes). In industrial environments DC current
is available in large quantities and is very lethal when handled improperly.
The severity of a shock largely depends on:
---Amount of current
---Amount of time on the exposure
---Resistance of the body.
AC:Alternating Current
AC in theory would allow your muscles time to be able to move so that you
could pull your hand / limb
away from whatever it was that was giving you the shock. This is so because
AC alternates from zero
to maximum (amplitude) in a specified time frame (frequency).It is during
this timeframe that muscle
signals may retract you hand/limb...
The time frame we are talking about here is only a few milliseconds-which
means that for larger
currents, there is no time for reflex action. However as I said above,
this largely depends on the amount of current flowing.

Starting current of motors (128A) would never give you a chance of even
thinking!
AC current will allow you to move your hand for the muscles which are not in
the path of the electric
current.In AC (Alternate Current) the muscles will contract and extend and
through the spasms you
might eventually free yourself (that is why people say that the current threw
them while, in fact,
it was their own muscles).

DC: Direct Current
Definitely DC. The passing of current through the muscles make them
contract.
In DC (Direct Current=0Hz) it will make your hand clamp the live wire; that
is why, when in doubt,
you should touch wires with the back of the hand. In AC (Alternate Current)
the muscles will contract
and extend and through the spasms you might eventually free yourself (that
is why people say that the
current threw them while, in fact, it was their own muscles). No time for
conscious efforts when under
current. Do not be fooled, NO ONE can sense the zero voltage "in between"
the 50Hz (cycles per second!!!).
People tend to underestimate DC because in normal life one encounters very
low dc voltages while the
mains ac is everywhere. Given the proper voltage DC will kill you. By the
way, it is not as much the voltage
as it is the current. A potentially lethal (depending on the health condition)
value starts from a 20mA current
through your body. The better the contact (e.g. wet hands, bare feet) the
lower the lethal voltage.

You better stay away of voltages over 24V (AC or DC) if you have no special
qualification. ---Electrical Engineer
If DC was used at 240v in household appliances then somebody would die
every day. AC is very safe then DC
at high voltages because it alters its charges. DC can be safely and easily
stored in low voltage in batteries
and that's why people have these wrong assumptions that DC is safe.
After the above arguments I have come to a conclusion that DC Current is
far more lethal than AC because:
DC will not release you at the point of contact with live conductor
DC will cause fibrillations in the heart leading it to stop due to overcontracted muscles.This is caused by
AC also but DC is more severe.DC causes a clench in hand muscles that’s
why when not sure, use the back of your hand.
The clenching causes the victim to grip the conductor and won’t let go.

G.I.S - Gas Insulated Substations #1
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A gas-insulated substation (GIS) uses a superior dielectric gas, sulfur hexafluoride (SF6), at a moderate
pressure for phase to phase and phase to ground insulation. The high-voltage conductors, circuit breaker,
interrupters, switches, current transformers, and voltage transformers are encapsulated in SF6 gas inside
grounded metal enclosures. The atmospheric air insulation used in a conventional, air-insulated
substation (AIS) requires meters of air insulation to do what SF6 can do in centimeters. GIS can therefore
be smaller than AIS by up to a factor of ten. A GIS is mostly used where space is expensive or not
available. In a GIS, the active parts are protected from deterioration from exposure to atmospheric air,
moisture, contamination, etc. As a result, GIS is more reliable, requires less maintenance, and will have a
longer service life (more than 50 years) than AIS. GIS was first developed in various countries between
1968 and 1972. After about 5 years of experience, the user rate increased to about 20% of new
substations in countries where space was limited. In other countries with space easily available, the
higher cost of GIS relative to AIS has limited its use to special cases. The IEEE [4, 5] and the IEC [6] have
standards covering all aspects of the design, testing, and use of GIS. For the new user, there is a CIGRE
application guide. IEEE has a guide for specifications for GIS.
What is Sulphur Hexafluoride SF6?

Sulfur hexafluoride is an inert, nontoxic, colorless, odorless, tasteless, and nonflammable gas consisting
of a sulfur atom surrounded by and tightly bonded to six fluorine atoms. It is about five times as dense as
air. SF6 is used in GIS at pressures from 400 to 600 kPa absolute. The pressure is chosen so that the
SF6 will not condense into a liquid at the lowest temperatures the equipment experiences. SF6 has two to
three times the insulating ability of air at the same pressure. SF6 is about 100 times better than air for
interrupting arcs. It is the universally used interrupting medium for high-voltage circuit breakers, replacing
the older mediums of oil and air. SF6 decomposes in the high temperature of an electric arc or spark, but
the decomposed gas recombines back into SF6 so well that it is not necessary to replenish the SF6 in
GIS. There are some reactive decomposition byproducts formed because of the interaction of sulfur and
fluorine ions with trace amounts of moisture, air, and other contaminants. The quantities formed are very
small. Molecular sieve absorbents inside the GIS enclosure eliminate these reactive by products over
time. SF6 is supplied in 50 kg gas cylinders in a liquid state at a pressure of about 6000kPA for
convenient storage and transport.

The Stockbridge Damper
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A Stockbridge damper is a tuned mass damper used to suppress wind-induced vibrations on taut cables,
such as overhead power lines. The dumbbell-shaped device consists of two masses at the ends of a
short length of cable or flexible rod, which is clamped at its middle to the main cable.It is placed about
midway between the nodes of the vibrations i.e. where amplitude of the vibrations would be more. The
vibration causes movement of the damper and energy is absorbed by the inter stand friction in the steel
cable. The vibrations have low amplitude up to 5mm and high frequency of 50Hz-100Hz. A typical damper
for use on a 132kV line is about 60cm long and weighs about 5kg.

THe 3Phase Syncronous Motors
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The 3phase synchronous motor is widely used in industries because it can be easily converted into Single
phase and 2phase.They are widely used in all Engineering field because their construction allows them to
be used for various purposes.

Characteristic Features of Synchronous Motors.
1. They run at synchronous speed. This machine will run at a constant speed which can be changed
by varying the supply frequency.
2. They are not self starting.-The rotor and stator fields have to be excited by a separate D.C excitation
voltage.
3. They can be operated under a wide range of power factors (whether lagging or leading).This is why
they are used for power-factor correction in power systems that have loads containing lagging power
factors.
Principle of Operation – How it works
When a 2phase winding is fed with a 3phase voltage supply, a magnetic field is produced according to
Faraday’s 1st law of Magnetism. Therefore a magnetic field of constant magnitude is produced where the
magnitude depends on the rate of magnetic flux according to Faraday’s 2nd Law of Magnetism. The
magnetic field produced rotates at a synchronous speed after the rotor has rotated half the period. The
rotor rotates back in the opposite direction because the direction of the induced current is opposing the
change in magnetic field. (Lenz Law).This is the reason why synchronous motors are not self starting. At
the half period point, the stator and rotor poles interchange their positions and therefore the motor rotates
in the reverse direction. Due to the continuous and rapid rotation of the stator and rotor poles, the rotor is
subjected to a torque which is rapidly reversing and that’s why a D.C excitation is required to start it. As
the load on the motor is increased, the rotor tends to fall back in phase but still continuous to run at
synchronous speed.
Procedure for Starting a Synchronous Motor.
1. The main field winding is short-circuited.
2. Reduced voltage with the help of an auto transformer is applied across the stator terminals.
3. The motor starts running.hen it reaches a steady speed as it will be judged with the wrecking
sound, a weak D.C is supplied by removing the short circuit in the main field winding.
4. If the excitation is sufficient, the machine is put into synchronization and it starts running at
synchronous speed.
5. Apply full supply voltage at the stator terminals by cutting out the auto transformer.
6. If you want to vary the power factor therefore you vary the D.C excitation. The motor maybe operated
at any desired power factor by changing the D.C excitation.
Application of 3 Phase Synchronous Motors
Power Factor Correction
Overexcited synchronous motors with a leading power factor are usually used for power factor for those
power systems which have a large number of induction motors and other devices having a lagging power
factor like welders and fluorescent lamps. They can be seen in large establishments like Universities,
Schools, Hospitals and Industries.
Constant Speed Applications
Because of high efficiency and high speed synchronous motors are used where constant speed is
required Example: Centrifugal Pumps, Belt Driven Reciprocating Compressors and Line Shafts.
Voltage Regulator
The voltage at the end of a long transmission line varies greatly when large inductive loads are present. If
the inductive loads are disconnected, suddenly, the voltage tends to rise considerably above its normal
value because of its line capacitance Xc. By installing a synchronous motor with field regulator; this
change in voltage can be controlled. This is called voltage regulation.

What Is 3-Phase Power?
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When a conductor is rotated to cut magnetic fields, some electromotive force is
induced according toFaradays Law. This voltage/emf is always in opposition to

the

main

field

E

=

according Lenz’s

Law
-Ndø/dt

The voltage induced by a single winding is known as single phase winding,
when rotated in a uniform magnetic field is known as single phase voltage.
A 3-Phase generator has 3 separate but identical conductors that are 120
Electrical degrees from one another. When the conductors are rotated in a
uniform magnetic field, the result is 3 independent supplies of equal voltages
which
are
displaced
from
each
other.
A 3-Phase supply is carried by 3 conductors known as lines which are
colored Red, Yellow & Blue. The currents in these cables are known as Line
Currents and the Voltages are known as Line Voltages. The 4th conductor,
known as Neutral is often used with the 3phase supply when the load is
unbalanced.
There are normally 2 connections to supply load with a 3-Phase supply:
1.
2.

Star Connection.
Delta Connection.

STAR CONNECTION

Where VB, VY, VR are Phase Voltages and VBY, VRB, VRY are Line Voltages.
Z is the Load Impedance. The load will be said to be balanced if ZR = ZB = ZY
At this point the current along the neutral conductor will be zero and hence we
shall not need the Neutral Conductor.

In Star connection, the Phase Current is always equal to Line Current.
i.e. ILINE = IPHASE VPHASE = √3* VPHASE
In Star Connection, of a 3-Phase supply, together with the Neutral conductor
allows the use of two voltages (Phase Voltage & Line Voltage).
If 4 wire system is used the load is not balanced.
DELTA CONNECTION

It is also known as Mesh Connection.
In this connection the ends of one load is connected to the start of the next
load. Phase voltages are always equal to line Voltages.
i.e. VPHASE = VLINE ILINE = √3*IPHASE
For power transmission a Delta system is associated with large Line currents
thus large crossectional area while the Star system is associated with large
Line Voltage. Loads connected in Delta Connection dissipate 3x (times) more
power than in star if the same supply. This is true because most motors which
have a high torque use the Delta connection.

Pole Mounted Sub-Stations
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I was going around town, with a colleague, we came across a structure which by the roadside that my
friend was quick to refer to as transformer. I quickly corrected him that its actual name is not a transformer
as many might call it, rather it’s called a Pole Mounted Sub-Station.
A Pole Mounted Sub-station is a large, free standing, outdoor electrical equipment that is mostly located
in residential places. Its main purpose is to step-down the lethal 11kV to 415/240V for light, commercial
and residential loads (consumers)...

The 11kV line is connected to the Step-Down Transformer (11kV/415V) though a gang isolator and fuses.
The lighting arrestors are installed on the H.T side to protect the Sub-Station from lightening strokes.
The transformer steps down the 11kV to 415V, 3phase, 4-wire supply. The voltage between any two
lines is 415V, and between any line and a phase is 240V. The Oil Circuit Breaker (O.C.B), installed on
the L.T side automatically isolates the transformer from the consumers in case of any fault. The Pole
Mounted Sub-stations are generally used fortransformer capacity up to 200kVA
They should be periodically checked for dielectric strength of oil in the transformer and (OCB)
In case of repair the transformer or (O.C.B) both the Gang Isolators and (O.C.B) should be shut off.
This equipment is very expensive leading to the reason why people vandalize them. The Step-Down
Transformer is oil cooled and its this oil that people steal. This costs the distribution company millions
of
Shillings annually. Please be warned that the current flowing through the transformer is deadly, it
would kill you in seconds. Stealing that oil means that the transformer will overheat, reduce its
efficiency and
possible explode under normal circumstances. In case you spot any one
vandalizing the equipment please call The Kenya Power and Lighting Co. Limited: www.kplc.co.ke.
See the image below of a Pole Mounted Sub-Station.

Electric Supply System
The conveyance of electric power from a power station to consumers’ premises is known aselectric supply
system. An electric supply system consists of three principal components viz., the power station, the
transmission lines and the distribution system.
The electric supply system can be broadly classified into
1.
2.

d.c. or a.c. system
overhead or underground system.

Now-adays 3-phase, 3-wire a.c. system is universally adopted for generation and transmission of electric
power as an economical proposition.

Typical a.c. Power Supply Scheme

Electric Supply Schematic

The network can be broadly divided into two parts viz.,
1.
2.

transmission system and
distribution system.

Each part can be further sub-divided into two—primary transmission and secondary transmission and
primary distribution and secondary distribution.
It may be noted that it is not necessary that all power schemes include all the stages.
(i)Generating station : In Fig, G.S. represents the generating station where electric power is produced by 3phase alternators operating in parallel. The usual generation voltage is 11 kV. For economy in the
transmission of electric power, the generation voltage (i.e., 11 kV) is stepped upto 132 kV (or more) at the
generating station with the help of 3-phase transformers.
The transmission of electric power at high voltages has several advantages including the saving of conductor
material and high transmission efficiency.
Generally the primary transmission is carried at 66 kV, 132 kV, 220 kV or 400 kV.
(ii) Primary transmission. The electric power at 132 kV is transmitted by 3-phase, 3-wire overhead system
to the outskirts of the city. This forms the primary transmission.
(iii) Secondary transmission. The primary transmission line terminates at the receiving station (RS) which
usually lies at the outskirts of the city. At the receiving station, the voltage is reduced to 33kV by step-down
transformers. From this station, electric power is transmitted at 33kV by 3-phase, 3-wire overhead system to
various sub-stations (SS) located at the strategic points in the city. This forms the secondary transmission.
(iv) Primary distribution. The secondary transmission line terminates at the sub-station (SS) where voltage
is reduced from 33 kV to 11kV, 3-phase, 3-wire. The 11 kV lines run along the important road sides of the
city. This forms the primary distribution. It may be noted that big consumers (having demand more than
50 kW) are generally supplied power at 11 kV for further handling with their own sub-stations.
(v) Secondary distribution. The electric power from primary distribution line (11 kV) is delivered to
distribution sub-stations (DS). These sub-stations are located near the consumers’ localities and step down
the voltage to 400 V, 3-phase, 4-wire for secondary distribution. The voltage between any two phases is 400
V and between any phase and neutral is 230 V. The single-phase residential lighting load is connected
between any one phase and neutral, whereas 3-phase, 400 V motor load is connected across 3-phase lines
directly.