Mechanical Design of Transmission Line (In context of Nepal)

May 1, 2023DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING 1

Mechanical Design Of Transmission Line(In context of Nepal)

PRESENTED BYSHULAB SHRESTHAThird Year


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 Lines1. Conductors 2. Supports: Towers, Poles3. Insulators: attached to supports and insulate the conductors from the ground.4. Cross arms: support to the insulators and conductor5. Guys and Stays: cables fastened to the poles to support the poles6. Lightening arresters: to discharge excess voltage due to lightening to earth7. Fuses and Isolation Switches: to isolate different parts of the overhead system8. Guard Wires: above or below power lines while crowing telephone line to prevent electromagnetic interference9. Miscellaneous items: Phase Plate, Danger Plate, Barbed Wire, Vibration Dampers


Main Components of Overhead Lines


Main Components of Overhead Lines

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 loadsii. Light in weightiii. Economical in cost and maintenanceiv. Longer lifev. 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 groundTo prevent potential hazard due to the leakage

Insulation required depends upon voltage levelMaterials: porcelain, glass, rubberIn 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_

%20NewSpotLight%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

Engineering

Mechanical Design of Transmission Line (In context of Nepal)