Mechanical Design of Transmission Line (In context of Nepal)

Mechanical Design Of Transmission Line
(In context of Nepal)
PRESENTED BY
SHULAB SHRESTHA
Third Year
17 October 2016DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING 1

Introduction:
WHY OVERHEAD LINES???
ELECTRICAL CONSIDERATIONS FOR TRANSMISSION LINE DESIGN:
 LOW VOLTAGE DROP
 MINIMUM POWER LOSS FOR HIGH EFFICIENCY OF POWER
TRANSMISSION.
 THE LINE SHOULD HAVE SUFFICIENT CURRENT CARRYING CAPACITY SO
THAT THE POWER CAN BE TRANSMITTED WITHOUT EXCESSIVE VOLTAGE
DROP OR OVERHEATING.

The underground cables are rarely used for power transmission due to two main
reasons.
installation costs for underground transmission will be very heavy.
proper insulation to the cables to withstand higher pressures.
Why Not UNDERGROUND CABLES???
Therefore, it has limited use for
distribution in congested areas where
safety and good appearances are the
main considerations.

Main Components of Overhead Lines
1. Conductors
2. Supports: Towers, Poles
3. Insulators: attached to supports and insulate the conductors from the ground.
4. Cross arms: support to the insulators and conductor
5. Guys and Stays: cables fastened to the poles to support the poles
6. Lightening arresters: to discharge excess voltage due to lightening to earth
7. Fuses and Isolation Switches: to isolate different parts of the overhead system
8. Guard Wires: above or below power lines while crowing telephone line to prevent
electromagnetic interference
9. Miscellaneous items: Phase Plate, Danger Plate, Barbed Wire, Vibration Dampers

GUYS AND STAYS
FUSE
BIRD
GUARDS
GUARD
WIRE
LIGHTENING
ARRESTORS

CONDUCTOR MATERIALS
• High Electrical Conductivity
• High Tensile Strength
• Low Cost
• Low Specific Gravity
• Easy Availability
• Not so brittle

COMMONLY USED CONDUCTOR MATERIALS
• Copper
• Aluminum
• Steel-Cored Aluminum
• Galvanized Steel
• Cadmium Copper

COPPER
• High Electrical Conductivity
 Low resistance = 16.78 nΩ•m at 20 °C
 High Current Density
• Greater Tensile Strength
• Small Cross Section Area
 Low wind resistance → less transverse load in tower
• Expensive
• Durable, high scrap value
• Scarcity

ALUMINUM
• Cheap and light compare to copper
• Less electrical conductivity and tensile strength
 Conductance = 60% that of copper for same cross section
 For same resistance areaAl = 1.26 areaCu
• Specific gravity of aluminum is less than copper.
 Less weight on supports
 generate greater swings hence large cross arms required
• Low melting point → cannot withstand short-circuit currents
• Used for low voltage distribution lines

STEEL CORED ALUMINUM
ASCR(Aluminum Conductor Steel Reinforced)
• Core of galvanized steel, aluminum conductors it outer layers
• Cross section ratio steel : Al is 1:6 (1:4 for high tensile strength)
• Increase tensile strength
 less sag
 greater span
 lesser tower height
• Universally used in transmission and
distribution

GALVANIZED STEEL
• High tensile strength → greater span
• Low conductivity → greater cross sectional area
• Eddy current and hysteresis loss
• Used in small power, small distance system where required cross
section is very low for ACSR or Copper

CADMIUM COPPER
• Cadmium and Copper alloy
• 1-2% cadmium is added to copper → increase tensile strength by 50%
• Long span is possible
• Expensive
• Used in small power where cross section required is small

SUPPORTS
Line supports should have following properties:
i. High mechanical strength to withstand the weight of conductors and
wind loads
ii. Light in weight
iii. Economical in cost and maintenance
iv. Longer life
v. Easy accessibility for conductors and insulators for maintenance

TYPES OF LINE SUPPORTS
1. Wooden Poles
 Cannot be used for high voltage > 20 KV
 Less mechanical strength
 Short life time 20-25 years

2. Steel Poles
 Greater mechanical strength
 Longer life 40 years
 Longer spans 50-80 m
 Lighter in weight

3. RCC Poles
 Reinforced Cement Concrete
 Greater mechanical strength
 Longer life than steel poles
 Longer spans 80-200 m
 Used for up to 33 KV
 Good insulating

4. Steel Tower
 Assembly of galvanized angle sections
 Used for long distance transmission and high voltage (>66 KV)
 Greater mechanical strength, longer life, longer spans than RCC or
steel poles
 High tower → lightening hazard → tower footing grounded to
bypass lightening

220 KV double circuit
transmission tower
220 KV single circuit
transmission tower
110 KV single circuit
transmission tower

IN CONTEXT OF NEPAL
Pre stressed concrete (PSC) Poles

IN CONTEXT OF NEPAL

INSULATOR
Line conductors should be insulated from support system
 to prevent leakage to ground
To prevent potential hazard due to the leakage
 Insulation required depends upon voltage level
Materials: porcelain, glass, rubber
In Nepal Porcelain insulator is largely used

INSULATOR
The insulators should have the following desirable properties :
1. High mechanical strength
2. High electrical resistance
3. High relative permittivity of insulator material in order that dielectric
strength is high.
4. High ratio of puncture strength to flashover.
5. Economical in cost and maintenance.

TYPES OF INSULATOR
Pin Type Suspension Type Strain Type
Shackle Stay

TRANSMISSION LINE CHALLENGES IN NEPAL
 There is no access to power for the approx. 58 percent of population.
 NEA has the monopoly in electricity.
 Over the period of 100 years, Nepal has built just 981 KM circuit of transmission line
 which clearly shows NEA has rarely shown any interest in the transmission line
 According to 20 year power generation report :- If Nepal’s economy had a capacity to
absorb 11500 MW (peak hour), it would have required 845 KM long 400 KV lines, the
total cost for which would have been Rs 41 billion and for 612 north south 400 KV
would required Rs 33 billion and for 612 north south 400 KV would require Rs 33
billion.
 If Nepal builds this transmission line, there will be a rush of investors to invest in
Nepal. In case, India agrees, even Nepal will be able to export its power to Bangladesh.

 NEA is planning to expand its transmission line to 3272 KM or circuit. This includes 78 kilometers of 33 KV,
1409 kilometers of 132 KV, 755 KM of 200 KV and 1030 KM of 400 KV in the coming ten years.
 to complete this project NEA needs huge amount of investment and manpower (technicians).
 The corridor transmission line projects include Kabeli Damak 132, Kosi corridor (Bashantapur-Kusha) 220
KV, Katari-Okhaldhunga, Solu, Singati-Lamosanghu,Sunkosi-Dolkha,Ramecchap –Garjyan-Khimti, Middle
Marsyangdi-Manang, Kaligandaki 220 KV, Katari-Okhaldhunga-Solu, Singati-Lamosanghu, Sunkosi-Dolkha,
Ramecchap-Garjyan-Khimit, Middle Marsyangdi-Manang, Karnali Corridor (Lamki-Upper Karnali)132 KV.
Under the absorption project are Thanko-Chapagaun-Bhaktapur, 132 KV, Syangja132 substation, Kamane
Substation, Kushum-Hapure 132 KV transmission line, Butwal-Kohalpur, Chapali 132, Matatirtha 132 kv
station. Similarly, the primary phase of project include Bajhang-Dipayal-Attariya Transmission line, Hapure-
Tulsipur Transmission line Surkhet-Dailekh-Jumla Transmission like, Kaligandai-Gulmi (Jhimruk)132 kv
Transmission line, Hetauda Butwal 400 KV Transmission line, Butwal-Lamki 400 KV Transmission line and
Lamki- Mahendranagar 400 KV Transmission line.

 Out of all those corridor transmission project NEA has completed just 2 projects.
Hetauda-Kamane 132/33kV Substation Matatirtha Substation Expansion work

 Without construction of transmission lines, one cannot expect any private investment
and even NEA cannot build any project.
 The government has no plans to construct the transmission line in the attractive power
generation sites like road.
 Land acquisition is one of the major challenges for the construction of transmission line.
 Construction of transmission line is matter of major debate and controversy.
 Even the government agrees to construct the transmission line; it has to face several
hurdles at the implementation stage from the people.
For instance, the second circuit of Heatuda Dhalkebar 132 KV Transmission line took a
decade to complete. Thankot, Chapagaun and Bhaktapur (132 KV) Transmission line
project was canceled due to opposition from people.

 Private investment company shows
hesitation in investment mainly for
one reasons lack of commitment on
the construction of transmission line
NEA Annual Report 2014

 Nepal-India Transmission line has another painful story to tell.
 Whether to import power from India or to export, Nepal needs grid connection with
India. With the fund available from the World Bank, Nepal-India agreed to complete the
Dhalkebar- Mujafarpur 400 KV transmission line by 2014. However, no progress has
been made yet on the project.
 The annual peak power demand of the Integrated Nepal Power System (INPS) in fiscal
year 2013/14 is estimated to be 1,201 MW, Compared to the preceding fiscal year’s
figure of 1,094.6 MW, the annual peak power demand of the INPS registered a
growth rate of 9.7 %.

 The dream to end the immediate load shedding of Nepal by importing electricity
through this grid seems to be just a dream.
 In conclusion, if NEA and government does not give grid development project the
upmost priority, Nepal seems to fail in development in Hydropower.

REFRENCES
 http://www.slideshare.net/Dhananjayjha2043/electrical-transmission-
line?related=2
 http://www.conceptohub.com/lesson/mechanical-design-of-overhead-
transmission/
 http://www.slideshare.net/search/slideshow?searchfrom=header&q=CONDUCTOR
 https://en.wikipedia.org/wiki/Transmission_tower
 http://www.tpub.com/neets/book4/11e.htm
 file:///C:/Users/Sulav/Downloads/Transmission%20Line%20Challenges%20_%20Ne
wSpotLight%20Nepal%20News%20Magazine.htm
 http://www.bnmahtogroup.com/industry_register/nepal-poles-industries-pvt-ltd/
 http://www.nea.org.np/anual-report.html
 Book : Principle of power System V.K. Mehta

THANK YOU

Mechanical Design of Transmission Line (In context of Nepal)

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