A summary of KEPCO's 345kV Marine Transmission Line Project

A summary of KEPCO’s 345kV Marine Transmission Line Project
Tai young Kim, Byung ho Kim and Chan hyeong Park
Power System construction office, KEPCO
5, 2Ga Namdaemoon-Ro Jung-Gu, Seoul, 100-092
Abstract
This paper describes the summary of design and construction technologies about KEPCO’s 345kV marine transmission
line. This has been operating commercially since July 2004 in Korea. We designed and constructed this line to supply the
enormous electric power stably from the Yonghung thermal power plant into the metropolitan area. We considered this
project in all aspects very deeply to decide design conditions and construction methods such as the electric environmental
design, insulation design, conductor design, selection of tower types and material, design of insulator strings, foundation
design, erection, wiring and so on because it crossed the western sea and lake Siwha about twenty five kilometers and
moreover we had not yet experienced in making a great plan of 345kV marine transmission line like this until now.
Keyword : 345kV, marine, transmission, technology
1. INTRODUCTION
Since the very first light bulb was lit in our country in
1887, we KEPCO have been contributing to industrial
development in Korea and improvements in the quality
of life for the nation by producing and providing high
quality electricity at very competitive prices for the past
century. The total consumption of electric power in
Korea is currently 51.3 million kilowatts, 45 percent of
which is being consumed in Seoul and the metropolitan
areas. Recently most of the electric power supplied to
metropolitan area has been transported from the power
plants located in southern and far eastern parts of the
Korea.
In this paper we would like to introduce the design &
construction methods of the 345kV marine Yonghung
transmission line that has been developed with pure
domestic technologies.
MY T/L outline is as following.
- Total length of line is about 39km (25km on the sea)
- Its power supply capacity is 12,000MW
- Steel pipe 137 towers (89 on the sea), 21,000 tons totally
80 ~ 165m high
- Wires are required approximately 1,900km.
- Used 6 types of porcelain insulators such as 210kN,
300kN, 400kN and Normal, Fog and totally 83,145
- Generating capacity of Yonghung Plant is 6,400MW
2. MAIN DISCUSSION
2.1 Outline of Transmission line
To cope with rapid growth of those areas as mentioned
above, 345kV marine Yonghung transmission lines
(hereinafter referred to MY T/L) were constructed from
Yonghung Island where the Thermal Power Plant was
built to Shinsiheung substation, crossing the western sea
and wide lake Sihwa. In the view of both effectiveness
and high technology applied to every stage of the
construction, MY T/L will indeed be the significant
project in the history of our power construction.
Picture 1. 345kV marine transmission line route
2.2 Insulation Design
2.2.1 Classification of Pollution Level
It is very difficult and long time to repair the MY T/L if it is
something wrong. We divided pollution level into two. It is
fixed “D” (over 0.25 less than 0.50 mg/cm2, ESDD) in the sea
and the lake Siwha, considering typhoon and seasonal wind.
In the land, it is settled “C”(over 0.125 less than 0.25 mg/cm2,
ESDD) taking into account of manufacturing complex areas.

2.2.2 Number of insulator of strings
We used the resistance voltage method to calculate the
number of insulator of strings instead of IEC 60815. The
resistance voltage of insulator for 345kV is 251kV.
362 kV × 3 × 1.2 = 251kV
The number of insulator can be given that the resistance
voltage divided by each insulator resistance voltage.
The number of insulator is shown as following table 1.
Items
Sea
lake
Land
Table 1. Number of insulator
Number of insulator
Type of
Insulator
Salt fog
(0.5mg/cm2)
Salt fog
(0.25mg/cm2)
Number Number
210kN 27
300kN 23
400kN 28
210kN 24
300kN 27
2.2.3 Insulator device
After the study of insulator strength, suspension type
insulator was determined 210kN x 2 strings on condition
that the horizontal span was less than 700m in the sea
section. If the horizontal span exceeded 700m, it would
be 300kN x 2 strings. For the strain type insulator, it
would be 400kN x 2 strings. In case of the land section,
suspension type insulator was selected 210kN x 2 strings
and strain type insulator was 300kN x 2 strings.
2.2.4 Arcing Horn
Arcing horn gap of insulator is the basic element in the
calculation of insulation distance. After considering the
required gap distance and horn efficiency by switching
over voltage and lightning surge, the arcing horn gap was
calculated. In case of 345kV marine Transmission line, it
didn’t only cross the sea section with no shelter, but also
there was some chance for lightning to concentrate on
the transmission line when lightning occurs, because of
height of tower. And it was very important for 345kV
marine Transmission line to transport a large capacity of
electricity. So we should reduce lightning flashover rate.
Table 2. Comparison of the lightning accident rate
Items
Horn distance
2,730mm 3,000mm 3,200mm Ref.
1 1.5560 1.1893 1.0118
2 1.3229 1.0065 0.8577
Item 1: All lightning Accident rate
Item 2: All lightning Accident rate except special type
As you see the table 2, to maintain the lightning accident
rate within one, it was recommended that arcing distance
was 3,000mm and installed SBI(lightning protector
device) in special tower.
2.2.5 Pre-fabricated Jumper
We selected Pre-fabricated jumper while horizontal angle
was below 40 degrees. If horizontal angle exceeded 40°,
we used string jumper or ‘V’ string. Pre-fabricated
jumper was used to improve work efficiency, because
thick conductor had been a problem to be formed and
handled. Pre-fabricated jumper supported jumper
conductor with spacer at the horizontal member. Prefabricated
jumper could decrease height of tower because
it maintained jumper conductor with horizon. It didn’t
need to have restraint swing reinforced conductor and it
was easy to control insulator distance through the
support device adjustment.
Picture 2. Pre-fabricated jumper
2.2.6 Length of Strings and depth of jumper
The length of suspension strings was 5,129 mm(210kN),
5,670mm(210kN) in land but 5,870mm(300kN) in sea.
The depth of jumper was 3,740mm applied to 110% of
the standard insulator distance
(1.115 x 3,000 + 21) x 110% = 3,740 mm
Table 3. Length of Strings (suspension type)
Items
Land Sea and lake
210kN 210kN 300kN
1 686 mm 686 mm 858 mm
2 4,080 mm 4,590 mm 4,485 mm
3 363 mm 363 mm 509 mm
4 5,129 mm 5,639 mm 5,852 mm
5 5,170 mm 5,670 mm 5,852 mm
Item 1: Hardware distance at arm
Item 2: Length of Insulator strings
Item 3: Hardware distance at conductor
Item 4: calculated distance
Item 5: total distance, Considering a margin
2.3 Design of Conductor
2.3.1 Selection of Conductor
The new type of conductor was developed and used for
this marine project, considering the characteristics of the
construction areas. In some cases, it was impossible to
avoid long distance span between the two towers.
Therefore it was selected as HTACSR/AW, High-

Strength Thermal-resistant Aluminum-alloy Conductors
Aluminum-clad Steel Reinforced. As a result, capacity of
transport was improved by 1.5 times compared to that of
the normal 345kV transmission line. The span (distance
between two towers) was extended from 350m to 600m,
and tensile strength was improved by 1.6 times from 11
tons to 18 tons.
To select the best suited conductor for marine project, we
were considering four kinds of conductors such as
HTACSR/AW 480 mm2 Cardinal, HTACSR/AW 480 mm2
Rail, TACSR/AW 480 mm2 Rail, TACSR/AW 480 mm2
Cardinal. After studying many kinds of the factors such
as capacity of transport, mechanical strength and
economical efficiency. We finally selected HTACSR/AW
480 mm2 x 4 bundles (Cardinal) for the sea section and
TACSR/AW 480 mm2 x 4 bundles (Rail) for the land
section.
Table 4. Character of conductor
Items unit TACSR/AW HTACSR/AW
Stranding
Num/ Al 45/3.7 54/3.38
mm St 7/2.47 7/3.38
Area mm2
Al 483.84 484.53
St 33.54 62.81
Ultimate
Strength
kgf 11,260 18,880
Diameter mm
Al 29.61 30.42
St 7.41 10.14
Weight kg/km 1,561 1,756
Resistance Ω/km 0.0595 0.0633
Temperature ℃ 150(max) 150 (max)
Permitted
current
A 1,431(max) 1,411(max)
Elastic coef kg/mm2 6,910 7,570
Coefficient /℃ 21.5x10 -6 20.5x10 -6
2.3.2 Capacity of Transport
Conductor should satisfy the 1,712 MW capacity of
transport because the whole generating power of the
Yonghung power plant was 6,400MW. We planned
four(4) circuits of marine transmission line.
Table 5. Capacity of transport
Items
TACSR/AW HTACSR/AW
(Rail) (Cardinal)
1 1,431 A 1,411 A
2 3,078 MW 3,035 MW
3 111 % 113 %
Item 1 : Continuous Current Capacity
Item 2 : Thermal Capacity of continuous current capacity
Item 3 : Overload Rate compared to thermal capacity for
one root accident(%)
Two types of conductors were all satisfied the capacity of
transport because overload rate compared to thermal
capacity for the one root accident is below 150%.
2.3.3 Ground Wire
Ground wire should be able to allow fault current to flow
when transmission line is failed. Ground wire tension
was determined to ensure that the sag at the lowest
temperature with no wind should not exceed 80% of the
conductor sag. By thinking over the induced current,
maximum fault current and mechanical characteristic, we
selected two conductors, AW 200 mm2 and OPGW 200 mm2.
2.3.4 Boltless type spacer damper
It is very difficult to maintain marine transmission lines,
because the towers were located on the sea. And we had
a few troubles with bolt type spacer damper in the past.
So the boltless type spacer dampers were developed to
prevent bolts from getting too loose. There are no
chances for these dampers to damage ACSR conductors.
2.4 Foundation Design
KEPCO adopted two special foundation methods to set
the tower in the sea. We selected Jacket Pile method and
altered it into individual jacket pile method. It was a safe
method to withstand any load of tower, wind load etc.
Picture 3. Jacket pile method
Steel Pipe Concrete method was used in lake Sihwa
where the “Jacket Pile” method could not be used and
some areas where the layer of the ground was not
suitable to support the structure. This method was highly
stable and cost effective.
Picture 4. Steel Pipe Concrete method

2.5 Tower Design
As tower materials are mostly used angle steel until now,
some problems happened in the maintenance and
construction because the towers are getting bigger due to
the shape of double-post. To resolve these problems in
the MY T/L, the steel pipe was fixed for safety and
reliability after studying the merits and demerits in using
the angle steel and the steel.
2.6 Construction Works
2.6.1 Erection
Towers are steel pipe. Generally we used a tower crane
to erect tower. Huge tower was over 150m high, it could
not be accomplished by ordinary tower crane. It was
required special cranes. We applied new method to erect
tower in the sea. It needed many kinds of equipment as
follows.
- one towboat
- three barges : set a crane, transport and store material
- hydraulic truck crane, crawler crane, tower crane.
300ton class sea cranes are used to erect towers in the sea.
Hydraulic crane that was set on barges were used for
towers up to 80m, and tower cranes were used for towers
over 80m
Picture 6. Drum site on the barge
2.7. Environment-Friendly Design
Deliberations with the Aviation Administration and local
officials resulted in the hiring of a color specialist who
designed the different colors used in painting the towers
to match the various characteristics of the areas. We
painted towers blue-green color in seashore area and
light yellow color in cultural asset area, light blue color
in factory area, light green color in resident areas, graygreen
in farm land, blue-green in sea light.
To remind people living nearby about the transmission
line of environment-friendly tower, we established shape
of bird and lighted it at night. And we installed nighttime
viewable illumination in lake Sihwa to protect birds and
improve image of electricity facilities
2.8 Air Pollution Counter Plan
Because some of the transmission line went adjacent to
manufacturing complex areas, there will be a corrosion
of the tower, conductor and hardware attached with SO 2
(sulfurous acid gas ) , NO 2 (nitrogenous oxide), T.S.P (total
suspended particle). After consulting with the specialist,
we made countermeasures as the following.
Picture 5. Tower Erection
2.6.2 Wiring
A large part of MY T/L route crosses bodies of water, so
different wiring methods were developed. Helicopters
and floating cranes helped install and separate electric
wires from the surface of the sea during the wiring stages
of the sections between Yonghung Island and Sunjae
Island where ships passes. Floating platforms were used
to perform this same task during wiring work in lake
Sihwa. To reduce the amount of work to be done in the
air above the sea while wiring and stringing wires, a
compromise method was used that was combining
conventional method and Pre-fabricated method.
This plan not only helped reduce working time but also
improved quality and wire loss. When working on
tension towers, wire compression works ere done about
50% on the ground.
Table 6. Countermeasure against air pollution
Items T.S.P Condition Counter measure
Tower Not clean by water painting
Insulator Can clean by water Install water pipe
Hardware
Conductor
Spacer
Jumper
possible to clean by
water
- remove TSP
by brushing
- coating
2.9 Transmission Tower Exposure Test
We had built the transmission tower exposure test site in
lake Siwha to improve life management of towers in the
MY T/L through assessment of corrosion protection and
concrete durability.
Test methods are as follows.
- Degradation evaluation of steel material coating
- Corrosion evaluation of steel material
- Concrete durability evaluation
- Lifetime analysis of Corrosion proof facility

4. REFERENCES
[1] Lee, sang-gyu etc, “The technology book of 345kV
yonghung transmission line project”, vol 1, 2003
[2] Kim, tai-young etc, “The technology book of 345kV
yonghung transmission line project”, vol 2, 2004
[3] “Manual for transmission tower exposure test”
KEPCO, August 2004
Picture 7. Transmission Tower Exposure Test
We had organized special team to make a systematic
study of the MY T/L, made a manual how to inspect
material samples in the Transmission Tower Exposure
Test. We have been studying all gained data and
analyzing the effects of the steel material degradation
and corrosion, concrete durability and Lifetime of facility.
3. CONCLUSION
MY T/L performed by purely domestic technologies
was completed in June of 2004, we have no error until
now. It means that we have independent technologies
on the design and construction of the ultra highvoltage
transmission facilities in the sea as well as the
facility reliability improvement by making regular
interval tests and progressing the technologies on the
design, construction, project management and check
& test based on power transmission construction
experience accumulated for the last 30 years.
Picture 8. View of erected towers in the sea