Application of High-Capacity Conductors for Uprating Transmission Lines Capacity in Nepal
Date
2023-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
IOE Pulchowk Campus
Abstract
Electricity demand and market penetration in Nepal is increasing day by day due to
increased industrialization, expand urbanization, large population density, change in
energy consumption habits of the consumers etc. Utility has to face multiple
challenges to expand new transmission line in urban and semi-urban areas due to lack
of availability of corridors triggered by the high real-estate cost, infrastructure
development, forest/ecology conversation etc. Additionally, transmission line projects
usually have limited execution schedule to comply with the increased load demand
and project completion to match with new hydropower projects. To maximize the
power transfer per unit RoW, replacing the old ACSR conductors with newly
developed HTLS conductors would be the best solution which have higher power
transfer capacity in the order of 2 to 3 times. Moreover, it can be completed in lesser
time span without any significant work and budget plan vis-à-vis a new line. The
same transmission line footprint might be used without any major modification in the
existing tower.
Load flow analysis of the INPS using the tool: DigSilent PowerFactory 15.1. is
carried out at different generation scenario considering the maximum load constant
throughout the study. Total internal generation of 2438.72 MW and maximum load of
2054.59 MW is recorded from secondary sources which are interconnected in INPS.
At 100% generation scaling, load flow result is noted with the surplus power of
230.07MW and the grid losses of 154.06 MW which accounts the loss of 6.31% of the
total system in-feed. At that scenario, ten (10) 132kV line sections (515.82 ckt.-km
length of ACSR Bear and 28 ckt.-km of ACSR Panther) is found to be overloaded by
more than 100%. Maximum line loading of 167.22% is noted at Dhalkebar-Mirchaiya
section (ACSR Bear) followed by 154.44% at Kusaha-Kataiya (ACSR Bear) section.
Gandak-Bardaghat line section having ACSR Panther conductor is also noted to be
overloaded by 116.03%. At decreased internal generation, power deficit is fulfilled by
the external in-feed which caused the total grid power loss to increase gradually.
Critical 132kV line sections found at 100% generation scaling are considered for
further analysis to use equivalent HTLS conductor. Replacement of insulators along
with erection accessories are also considered in the study.
ACCC OSLO conductor having equivalent cross section, weight per unit length and
meeting required ultimate tensile strength is considered as equivalent conductor and
found the most compactible for both ACSR conductor types. ‘IEEE 738 Standard’ is
applied to calculate the derated current carrying capacity of the candidate HTLS
conductor under NEA service condition which is found to be 2.45 times higher than
ACSR Bear and 2.84 times higher than ACSR Panther conductor for the value of
maximum allowable current which is quite satisfactory to consider as an equivalent
conductor. Line loading is reduced drastically at all critical line section after
conductor uprating viz. a maximum value of 62.78% at Lamosanghuv- Khimti section
and 54.83% at Dhalkebar - Mirchaiya section. Line loading value of 25.57% is
minimum at Gandak- Bardaghat section. It is also remarkable that the surplus power
in INPS generation is found to be 245.67 MW which is more by 15.60 MW than the
case before. It means grid power loss is decreased by 15.60 MW which is only 5.67%
of total internal generation and it was 6.31% before conductor replacement.
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Sag-tension analysis of old ACSR and HTLS ACCC OSLO conductors is also carried
out using PLS-CADD tool to study the behavior at different weather cases. It’s all
complied the required criteria for not violating the existing sag at any operating
temperature condition of each individual conductor.
Total cost estimated for conductor replacement is found to be USD 25.798 Million
which is almost equivalent to set up a new 15.60 MW hydropower plant and it is
considered as an analogy of grid power loss reduction after conductor replacement.
The test of old ACSR conductors, insulators, erection hardware and fitting accessories
etc. is recommended as per prevailing IS/BS at accredited laboratory to find the
remaining useful life and its technical viability to re-use in new/old transmission lines.
Description
Almost all the existing transmission lines in Nepal are overhead due to economy.
Existing high voltage transmission line in Nepal are 78 Circuit Kilometers (Ckt. km)
length of Dhalkebar-Muzzarffarpur 400 kV Cross Border Transmission Line, 524.60
Ckt. km length of 220 kV including 5 Ckt. km length of 220 kV Double Circuit
Underground in Matatirtha – Matatirtha Substation in Kathmandu; 3,459.54 Ckt. km
length of 132 kV Transmission Line and 514.46 Ckt. km length of 66 kV
Transmission Line.
Keywords
ACSR conductors, HTLS conductors