PS Lecture1 introduction to power systems

Introduction to Power
Systems(ECEG-3176)
Addis Ababa University
Addis Ababa Institute of Technology (AAiT)
School of Electrical & Computer Engineering
Instructor: Awraris Getachew

Evolution of Electric Power Systems
AAiT, School of Electrical & Computer Engineering, Addis Ababa, Ethiopia
1
An electric power system is a network of electrical components
deployed to supply, transfer, store, and use electric power
The first complete electric power system was built by Thomas
Edison- the historic Pearl Street Station in New York City which
began operation in September 1882.
• Comprising a generator, cable, fuse, meter and loads.
• It was dc system:-steam engine driven dc generator
• 59 customers in 1.5 km radius
• Load: incandescent lamps
• Underground cable system, 110 v

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2
Within a few years similar systems were in operation in most
large cities throughout the world.
With the development of motors by Frank Sprague in 1884,
motor loads were added to such systems.
By 1886, the limitations of dc systems were becoming
increasingly apparent. They could deliver power only a short
distance from the generators.

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3
L.Gaulard and J.D. Gibbs of Paris, France developed transformer
and ac transmission.
In 1886, William Stanley developed and tested a commercially
practical transformer and ac distribution system for 150 lamps at
Great Barrington, Massachusetts.
In 1889, the first ac transmission line in North America was put
in to operation. It was a single phase line transmitting power at
4,000 V over a distance of 21 km.

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4
With the development of poly phase systems by Nikola Tesla,
the ac system became even more attractive.
In the 1890s, there was considerable controversy over whether
the electric utility industry should be standardized on dc or ac.
There were passionate arguments between Edison, who
advocate dc, and Nikola Tesla, who favored ac.

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5
 By the turn of the century, the ac system had won out over the
dc system for the following reasons:
 Voltage levels can be easily transformed in ac systems, thus
providing the flexibility for use of different voltages for
generation, transmission and consumption.
 AC generators are much simpler than dc generators.
 AC motors are much simpler and cheaper than dc motors.

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6
 The first three phase line in North America went in to
operation in 1893 , a 2300V, 12km line.
 In the early period of ac power transmission,
frequency was not standardized.
 Many different frequencies were in use: 25, 50, 60,
125 and 133 Hz.
 60 Hz was adopted as standard in North America and
many other countries use 50 Hz.

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7
 The increasing need for transmitting larger amounts of power
over longer distances created an incentive to use progressively
higher voltage levels.
 To avoid the proliferation of an unlimited number of voltages,
the industry has standardized voltage levels.
 With the development of mercury arc valves in the early 1950s,
high voltage dc (HVDC) transmission systems became
economical in special situations.
 The cross over point beyond which dc transmission may become
a competitive alternative to ac transmission is around 500 km
for over head lines and 50 km for underground or submarine
cables.

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8
 HVDC transmission also provides an asynchronous link
between systems where ac interconnection would be
impractical because of system stability considerations
or because nominal frequencies of the systems are
different.
 The first modern commercial application of HVDC
transmission occurred in 1954 when the Swedish
mainland and the island of Gotland were
interconnected by a 96 km submarine cable.

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9
 With the advent of thyistor valve converters, HVDC
transmission became even more attractive.
 The first application of an HVDC system using thyristor
valves was at Eel River in 1972.
 With the cost and size of conversion equipment
decreasing and its reliability increasing, there has
been a steady increase in the use of HVDC
transmission.

Sources of Energy
10
The major sources of primary energy are:
 Fossil fuels: coal, natural gas and oil
 Water power: Hydroelectric power
 Nuclear power: fission and fusion
 Solar energy: heat radiation from the sun
 Geothermal energy: thermal springs due to inner strata of
earth at a very high temperature
 Wind power: wind turbines
 Tidal power: tides of ocean

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11
 Share of global electricity

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12
Fossil fuel thermal power plant

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13
Cross-section of a fossil fuel-fired thermal power plant

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14
Hydro-electric power plant
Gilgel Gibe III Dam

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15
Cross-section of a hydro-electric power plant

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16
Nuclear power plant

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17
Cross-section of a nuclear power plant

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18
Wind power plant

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19
Solar Power

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Geothermal power plant

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21
Tidal power plant

AC and DC transmission
22
Comparison of AC and DC Transmission
 Electric Power can either be transmitted by means of AC or DC
Advantages of DC Transmission:
 Power transmission by means of DC requires only two conductors as
compared to three conductors required for AC.
 There is no inductance, capacitance, phase displacement and surge
problem in DC transmission.
 Due to absence of inductance, the voltage drop in DC transmission is
less than the AC transmission for same load and receiving end
voltage.
 A DC transmission line has less Corona and hence efficiency is
improved.
 In DC transmission, there is no stability and synchronization problem.

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23
Disadvantages of DC Transmission:
 DC Power generation is difficult due to commutation problem.
 Transformer does not work for DC and therefore voltage level of DC
cannot be changed for power transmission.
 DC Switches and Circuit Breakers have their own limitations

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24
Advantages of AC Transmission:
 AC power can be generated at high voltage. The maximum voltage at
which Electrical Power is generated can be 21 kV.
 AC voltage can be stepped up for power transmission at high voltage.
Disadvantages of AC Transmission:
 AC transmission requires more conductor material as compared to DC
transmission.
 The construction of AC transmission line is more complicated as
compared to DC transmission line.
 Due to Skin Effect in AC transmission, the effective resistance of
conductor increases.

Cont’d…
.
Cost comparison of HVDC and HVAC overhead transmission lines
25

3 phase vs Single phase systems
26
Advantages of a three phase system over a single phase power
system
 The rating, i.e. the output of a three-phase machine is nearly
1.5 times the rating (output) of a single phase machine of the
same size
 In single phase circuits, the power delivered is pulsating.
Whereas, in the polyphase system, the power delivered is
almost constant when the loads are in balanced condition
 Single Phase induction motors are not self starting as it does
not have starting torque, where as Three phase induction
motors are self starting.

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27
 In 3 phase motor, the frequency of vibrations is less as compared to
single phase motor because in single phase the power transferred is a
function of time and varies constantly
 3 Phase system requires less copper and aluminum for the
transmission system in comparison to a single phase transmission
system.
Disadvantages of 3 phase system over single phase
 Unbalanced loading ( can cause voltage fluctuations )
 Complex System (requires symmetrical components for analysis and
operation )
 Phase Sequence needed to be kept in mind while making connections

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28
 Electrical systems vary in size and structural components.
 However, they all have the same basic characteristics.
 Generation system
 Transmission system
 Sub-transmission system
 Distribution system

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29

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PS Lecture1 introduction to power systems

PS Lecture1 introduction to power systems

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PS Lecture1 introduction to power systems