A Summary of KEPCO’s 345kV Marine Transmission Line Project

7/25/2019 A Summary of KEPCOs 345kV Marine Transmission Line Project

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A summary of KEPCOs 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 KEPCOs 345kV marine transmissionline. 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 environmentaldesign, insulation design, conductor design, selection of tower types and material, design of insulator strings, foundationdesign, erection, wiring and so on because it crossed the western sea and lake Siwha about twenty five kilometers andmoreover 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 in1887, we KEPCO have been contributing to industrialdevelopment in Korea and improvements in the qualityof life for the nation by producing and providing highquality electricity at very competitive prices for the pastcentury. The total consumption of electric power inKorea is currently 51.3 million kilowatts, 45 percent of

which is being consumed in Seoul and the metropolitanareas. Recently most of the electric power supplied to

metropolitan area has been transported from the powerplants located in southern and far eastern parts of theKorea.

In this paper we would like to introduce the design &

construction methods of the 345kV marine Yonghungtransmission line that has been developed with pure

domestic technologies.

2. MAIN DISCUSSION

2.1 Outline of Transmission lineTo 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 wasbuilt to Shinsiheung substation, crossing the western seaand wide lake Sihwa. In the view of both effectivenessand high technology applied to every stage of theconstruction, MY T/L will indeed be the significant

project in the history of our power construction.

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

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 issomething wrong. We divided pollution level into two. It is

fixed D (over 0.25 less than 0.50 mg/, 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/,

ESDD) taking into account of manufacturing complex areas.


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2.2.2 Number of insulator of strings

We used the resistance voltage method to calculate thenumber of insulator of strings instead of IEC 60815. Theresistance voltage of insulator for 345kV is 251kV.

2.13362 kV = 251kV

The number of insulator can be given that the resistancevoltage divided by each insulator resistance voltage.The number of insulator is shown as following table 1.

Table 1. Number of insulator

Number of insulator

Salt fog

(0.5mg/)

Salt fog

(0.25mg/)Items

Type of

Insulator

Number Number

210kN 27

300kN 23Sea

lake400kN 28

210kN 24Land300kN 27

2.2.3 Insulator device

After the study of insulator strength, suspension typeinsulator was determined 210kN x 2 strings on conditionthat the horizontal span was less than 700m in the seasection. If the horizontal span exceeded 700m, it wouldbe 300kN x 2 strings. For the strain type insulator, itwould be 400kN x 2 strings. In case of the land section,

suspension type insulator was selected 210kN x 2 stringsand strain type insulator was 300kN x 2 strings.

2.2.4 Arcing HornArcing horn gap of insulator is the basic element in thecalculation of insulation distance. After considering therequired gap distance and horn efficiency by switchingover voltage and lightning surge, the arcing horn gap wascalculated. In case of 345kV marine Transmission line, itdidnt only cross the sea section with no shelter, but alsothere was some chance for lightning to concentrate onthe transmission line when lightning occurs, because of

height of tower. And it was very important for 345kVmarine Transmission line to transport a large capacity of

electricity. So we should reduce lightning flashover rate.

Table 2. Comparison of the lightning accident rateHorn distance

Items 2,730mm 3,000mm 3,200mmRef.

1 1.5560 1.1893 1.0118

2 1.3229 1.0065 0.8577

Item 1: All lightning Accident rateItem 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 distancewas 3,000mm and installed SBI(lightning protectordevice) in special tower.

2.2.5 Pre-fabricatedJumperWe selected Pre-fabricated jumper while horizontal anglewas 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 andhandled. Pre-fabricated jumper supported jumper

conductor with spacer at the horizontal member. Pre-fabricated jumper could decrease height of tower because

it maintained jumper conductor with horizon. It didntneed to have restraint swing reinforced conductor and itwas easy to control insulator distance through thesupport 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 (210kN),

5,670mm(210kN) in land but 5,870mm(300kN) in sea.The depth of jumper was 3,740mm applied to 110% ofthe standard insulator distance

(1.115 x 3,000 + 21) x 110% = 3,740 mm

Table 3. Length of Strings (suspension type)

Land Sea and lakeItems

210kN 210kN 300kN

1 686 686 858

2 4,080 4,590 4,485

3 363 363 509

4 5,129 5,639 5,852

5 5,170 5,670 5,852Item 1: Hardware distance at arm

Item 2: Length of Insulator stringsItem 3: Hardware distance at conductorItem 4: calculated distanceItem 5: total distance, Considering a margin

2.3 Design of Conductor

2.3.1 Selection of ConductorThe new type of conductor was developed and used for

this marine project, considering the characteristics of theconstruction areas. In some cases, it was impossible to

avoid long distance span between the two towers.

Therefore it was selected as HTACSR/AW, High-


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Strength Thermal-resistant Aluminum-alloy ConductorsAluminum-clad Steel Reinforced. As a result, capacity oftransport was improved by 1.5 times compared to that ofthe 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 11tons to 18 tons.

To select the best suited conductor for marine project, wewere considering four kinds of conductors such as

HTACSR/AW 480 Cardinal, HTACSR/AW 480

Rail, TACSR/AW 480 Rail, TACSR/AW 480

Cardinal. After studying many kinds of the factors suchas capacity of transport, mechanical strength andeconomical efficiency. We finally selected HTACSR/AW

480 x 4 bundles (Cardinal) for the sea section and

TACSR/AW 480 x 4 bundles (Rail) for the land

section.

Table 4. Character of conductorItems unit TACSR/AW HTACSR/AW

Al 45/3.7 54/3.38Stranding

Num/mm St 7/2.47 7/3.38

Al 483.84 484.53Area

St 33.54 62.81

Ultimate

Strengthkgf 11,260 18,880

Al 29.61 30.42Diameter

St 7.41 10.14

Weight kg/km 1,561 1,756

Resistance /km 0.0595 0.0633

Temperature 150(max) 150 (max)

Permittedcurrent

A 1,431(max) 1,411(max)

Elastic coef kg/ 6,910 7,570

Coefficient / 21.5x10-6

20.5x10-6

2.3.2 Capacity of TransportConductor should satisfy the 1,712 MW capacity oftransport because the whole generating power of theYonghung power plant was 6,400MW. We plannedfour(4) circuits of marine transmission line.

Table 5. Capacity of transport

Items TACSR/AW(Rail)

HTACSR/AW(Cardinal)

1 1,431 A 1,411 A

2 3,078 MW 3,035 MW

3 111 % 113 %

Item 1 : Continuous Current CapacityItem 2 : Thermal Capacity of continuous current capacityItem 3 : Overload Rate compared to thermal capacity for

one root accident(%)

Two types of conductors were all satisfied the capacity oftransport because overload rate compared to thermalcapacity for the one root accident is below 150%.

2.3.3 Ground Wire

Ground wire should be able to allow fault current to flowwhen transmission line is failed. Ground wire tensionwas 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 and OPGW 200.

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 toprevent bolts from getting too loose. There are nochances for these dampers to damage ACSR conductors.

2.4 Foundation Design

KEPCO adopted two special foundation methods to setthe tower in the sea. We selected Jacket Pile method andaltered it into individual jacket pile method. It was a safemethod to withstand any load of tower, wind load etc.

Picture 3. Jacket pile method

Steel Pipe Concrete method was used in lake Sihwawhere the Jacket Pile method could not be used andsome areas where the layer of the ground was notsuitable to support the structure. This method was highlystable and cost effective.

Picture 4. Steel Pipe Concrete method


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2.5 Tower Design

As tower materials are mostly used angle steel until now,some problems happened in the maintenance andconstruction because the towers are getting bigger due to

the shape of double-post. To resolve these problems inthe MY T/L, the steel pipe was fixed for safety andreliability after studying the merits and demerits in usingthe angle steel and the steel.

2.6 Construction Works

2.6.1 Erection

Towers are steel pipe. Generally we used a tower craneto erect tower. Huge tower was over 150m high, it couldnot be accomplished by ordinary tower crane. It was

required special cranes. We applied new method to erecttower 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 fortowers up to 80m, and tower cranes were used for towersover 80m

Picture 5. Tower Erection

2.6.2 Wiring

A large part of MY T/L route crosses bodies of water, sodifferent wiring methods were developed. Helicoptersand floating cranes helped install and separate electricwires from the surface of the sea during the wiring stagesof the sections between Yonghung Island and SunjaeIsland where ships passes. Floating platforms were usedto perform this same task during wiring work in lake

Sihwa. To reduce the amount of work to be done in theair above the sea while wiring and stringing wires, acompromise method was used that was combiningconventional method and Pre-fabricated method.This plan not only helped reduce working time but alsoimproved quality and wire loss. When working on

tension towers, wire compression works ere done about50% on the ground.

Picture 6. Drum site on the barge

2.7. Environment-Friendly Design

Deliberations with the Aviation Administration and localofficials resulted in the hiring of a color specialist who

designed the different colors used in painting the towersto match the various characteristics of the areas. Wepainted towers blue-green color in seashore area andlight yellow color in cultural asset area, light blue colorin factory area, light green color in resident areas, gray-green in farm land, blue-green in sea light.To remind people living nearby about the transmissionline of environment-friendly tower, we established shapeof bird and lighted it at night. And we installed nighttimeviewable illumination in lake Sihwa to protect birds and

improve image of electricity facilities

2.8 Air Pollution Counter PlanBecause some of the transmission line went adjacent tomanufacturing complex areas, there will be a corrosionof the tower, conductor and hardware attached with SO2(sulfurous acid gas), NO2 (nitrogenous oxide), T.S.P (totalsuspended particle). After consulting with the specialist,we made countermeasures as the following.

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

ConductorSpacer

Jumper

possible to clean bywater

- remove TSP

by brushing- coating

2.9 Transmission Tower Exposure TestWe had built the transmission tower exposure test site in

lake Siwha to improve life management of towers in theMY T/L through assessment of corrosion protection andconcrete 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


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Picture 7. Transmission Tower Exposure Test

We had organized special team to make a systematicstudy of the MY T/L, made a manual how to inspectmaterial samples in the Transmission Tower Exposure

Test. We have been studying all gained data andanalyzing the effects of the steel material degradationand corrosion, concrete durability and Lifetime of facility.

3. CONCLUSION

MY T/L performed by purely domestic technologieswas 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 high-voltage transmission facilities in the sea as well as the

facility reliability improvement by making regularinterval tests and progressing the technologies on the

design, construction, project management and check

& test based on power transmission constructionexperience accumulated for the last 30 years.

Picture 8. View of erected towers in the sea

4. REFERENCES

[1] Lee, sang-gyu etc, The technology book of 345kVyonghung 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

Documents

A Summary of KEPCO’s 345kV Marine Transmission Line Project