construction of 230 kv und cable

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International Symposium on Underground Excavation and Tunnelling

2-4 February 2006, Bangkok, Thailand

Construction of 230 kV Underground Power Lines Between

Lardprao and Vibhavadi Terminal Stations

S. Soponkanaporn1

1Director of Research and Development Department, Metropolitan Electricity Authority (MEA), Bangkok

ABSTRACT

This paper introduces the application of the pipe jacking techniques used in the construction of the first

biggest tunnel for electrical power distribution between Lard Prao and Viphavadi Terminal Stations for

Metropolitan Electricity Authority (MEA). The civil, mechanical, and electrical engineering experiences

are adopted for construction of shafts and tunnels, 230 kV power cable installation, ventilation and cooling

system, resulting in securing the high reliability electricity distribution in the densely commercial area in

Bangkok.

1. INTRODUCTION

The 230 kV Underground Power Cable between Lardprao and Vibhavadi Terminal Stations project was

included in the 8th

Power Distribution System Improvement and Expansion Plan under the project, MEA

at its Vibhavadi Terminal Station will receive power from Electricity Generation Authority of Thailand

(EGAT)’s Lardprao Terminal Station through 230 kV underground cable before transmitting to 69-115 kV

distribution substations. This sufficiently serves the increasing power demand in shopping centers and

business areas as well as reinforces the optimal power system reliability.

Construction of incoming

Construction of outgoing

Construction of Vibhavadi Terminal Station and installation of electrical equipment

2. SCOPE OF WORK

This project will be constructed on a turnkey basis. It covers design, construction of 21 manholes and 2.6

meter diameter tunnel with the total length of 8 km. The two circuits of 230 kV oil filled cable are

installed in cable trough of which the temperature will be controlled by cool water pipe installed

inparallelled. The others include the secondary line lighting, communication and ventilation systems aswell as cooling station. The tunnel is also planned for the addition of one circuit of 230 kV and two

circuits of 115 kV in the future (Figure 1).

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Detailed information about this project

Construction contract signing 13 March 1999

Completion date 12 October 2002

(1,320 days)

Total investment cost ฿ 3,940 million

comprises

- Cable and accessories ฿ 2,140 million

- Domestic and foreign transportation ฿ 65 million

(inclusive of insurance)

- Engineering services ฿ 135 million

- Civil work and installation ฿1,600 million

Manhole interval 500 meters

Manhole Depth 15 meters

Concrete reinforced tunnel

- Inner diameter 2.6 meters

- Outer diameter 3.04 meters- Tunnel length per section 2.43 meters

Tunnel Boring Machine : Earth Pressure Balance

- Diameter 3.05 meters

- Total length 10.40 meters

230 kV oil filled cable

- Copper conductor 2,500 sq.mm

- Polyproprelene Laminated Paper insulated (PPLP)

- PVC cover

Cooling system

- Shell type compressor

- HCHC – 134a Refrigerant

- 300 USRT Ventilation system

- Blowers installed at 4 manholes

Communication system via Fiber-optic

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Figure 1. Electrical Tunnel Configuration

3. CIVIL CONSTRUCTION METHODOLOGY

Construction of by pass and removal of existing infrastructure. Before the project construction, the

existing infrastructure such as drainage canal, water pipe, telephone wire obstructing the line route of

manholes must be removed.

Construction of Manholes

The manholes will be produced in 6 separate parts and be molded at the site. This manhole will be lowered

under the ground by hydrolic. Bentonite is used to lubricate the outer manhole and the ground (Figure 2).

Figure 2. Manhole Construction Figure 3. Tunnel Construction

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Tunnel Construction

Power earth pressure balance jacks are used to push the pipes through the ground behind a shield at the

same time as excavation is taking place within the shield. The soil will be cautiously removed by

mechanical tool in order to control balance of the soil pressure in and out of the tunnel in an avoidance of

disturbance to nearby construction. The reinforced concrete pipe will be jacked from one manhole to thenext until the end of the route. During the jacking operation, polymer will be pumped around the outside

of the pipe to reduce resistance which will accordingly reduce damage over the pipe. Next, the concrete

will be laid on the tunnel surface for further cable installation and maintenance (Figure 3).

4. 230 KV CABLE INSTALLATION

The cable pullers will be installed at three different locations; namely at the top and bottom of the

manhole, and the last along the tunnel. The control will be made remotely from the Control Room. In case

of any problem with the pulling speed from the three locations, the Controller will immediately stop the

cable pulling. Once the cable has been put in the tunnel in between two manholes, the cable will then be

lifted and laid in the cable trough set on supporting structure while the cable will be fastened with cable

cleat (Figure 4).

Figure 4. 230 kV Cable Installation

5. COOLING SYSTEM

The cooling system is also installed at Mohchit Distribution Substation to pump cool water through the

pipe which is laid out along with the cable. This will reduce the temperature in the tunnel and keep the

power supply at its normal condition (Figure 5).

Apart from the cooling, the oil supply system was also installed from pressure tank located at

Lardprao and Vibhavadi Transmission Stations to control temperature and pressure of oil within the cable.

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Figure 5. Cooling System Figure 6. Ventilation System

6. VENTILATION SYSTEM

The main purpose is to prevent oxygen shortage and ventilate the fresh air to the maintenance crews who

working the tunnel, eight ventilation fans (2 sets / manhole) are installed with the wind velocity higher than

1 m/s in every point of the tunnel. To limit the noise generated by the ventilation fans, a silencer was

installed, and the specification stipulated that the noise level outside the shaft at the nearest building shall

be less than 70 dB.

If fire is detected by the fire sensors in the manholes, the control volume dampers at the ventilation

shaft will be automatically closed in order to limit the oxygen in the tunnel and all ventilation fans will be

automatically shut down. The system will be locked until the fire is stopped. All control volume dampers

have to be opened manually (Figure 6). 7. COMMISSIONING TEST

Once the construction has been completed, major equipment will be tested separately. The final

commissioning test will be done again later before starting the project (Figure 7).

Figure 7. Commissioning test configuration

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8. CONCLUSIONS

The project had been completed before contract schedule with satisfactory accepted by all parties which

are MEA, the construction contractors and the construction supervision consultants. The key performance

success is due to the best co-operation, truly and open-mind discussion, work progress follow up and

solving problem effectively. This project has been serviced to distribute huge electrical power to

strengthen the transmission line network and bring to customers with high reliable electricity.

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