CEPCO, Saudi Arabia is very proud to announce the completion and the achievement of the complex and innovative solution that allowed the 4000 MVA power to be transmitted between Rabigh PP and AL ADL 380 KV BSP in western region of Saudi Arabia.
CEPCO has executed this contract consisting of 8 km long cable route between OHL gantry Rabigh and AL ADL BSP in Jeddah as 2×380 KV cable circuits 2 cables per phase.
This project can be classified as a 1st contract of its kind executed in Saudi Arabia due to its special nature that imposed an innovative solution without which, the 4000 MVA 380 KV power supply would not have been possible to be delivered to AL ADL BSP.
Civil Works Challenges:
The biggest challenge was to find a way on how to construct the last 620m section No. 16 of the 8 Km route that had to cross the very busy traffic under Al Haramain Highway, and below the bulk oil main supply pipeline of Aramco, coupled with the extremely congested area with all kinds of underground services like;
• 380 KV 110 KV Lines
• Drinking water, flood and sewerage lines
• Telecommunication lines
The proposed only solution was to construct;
• A cast in situ reinforced concrete square tunnel over a length of 270m to allow the laying of up to six 380 KV cable circuits.
• A receiving shaft B (11m deep, 7-meter diameter).
• A 109m long micro deep tunnel consisting of 2 reinforced concrete pipes each 2.2-meter inner diameter each to allow for the laying of 3x380 KV cable circuits (12 meters deep, below the Aramco bulk oil supply pipeline running under the Al Haramin highway. Here the thrust boring and pipe jacking method was used at the 1st time in Saudi Electric Company underground power cable transmission links.
• The 2 micro tunnel pipes are running between the sending shaft A (14m deep; 12-meter diameter) and the receiving shaft B (11m Deep,7m diameter) to allow for the introduction and extraction of the thrust boring head and pipe jacking equipment associated with continuous mud lubricant injected continuously to facilitate the underground thrust boring works.
Shaft A is also used as a transition area between the deep micro tunnel and the 211m square tunnel at AL ADL substation basement to reach the 380 KV GIS cable compartments.
The standard SEC design of the lying depth of 380 KV cables transmission capacity of 4×1000 MVA is 2 meters.
However, in section 16 at the tunnel area, the depth of the micro tunnel is 12 meters, such depth would decrease the transmission capacity by more than 50%.
Therefore, a forced cooling central air conditioning system had to be constructed in order to guarantee the 4000 MVA transmission capacity.
For that CEPCO had to construct a special HVAC building with AHU (Air Handling Units), air circulation jet fans placed through the tunnel system, and a hot air discharge fan building at the far end of the square tunnel.
Major Challenges encountered during the performance of tunnel construction works in Section 16:
• The daily traffic permits and the usual permits from various utilities and authorities. Those have taken very long time to obtain (NWC, municipality etc.).
• The engineering studies approvals and revisions were time consuming, because of the implementation of this new concept within SEC approved regulations.
• Very congested underground services in the area of the square tunnel, which imposed that the complete square tunnel had to be constructed below these services (the tunnel roof is more than 2.5 meters below the asphalt level and the tunnel bottom slab is located at around 6m below the asphalt. To protect these services from being damaged during the excavation works, a very extensive and expensive mechanical protection supporting system had to be made, and micro excavation machinery had to be used, combined with manpower hand works. In addition, very expensive shoring system had to be used to prevent the (6.5-7.0m) deep excavated area from collapsing.
• Underground continuous water leakage and seepage into the (deep shafts A, B and the deep micro tunnel area) had to be drained and pumped out continuously in order to reach a dry condition necessary for the concrete pouring works, having for consequence a long delay in the execution of the works.
• The 380 KV 1x2500mm² 65 kgs/m weight cable pulling works was extremely difficult and slow and needed a very experienced cable pulling team equipped with special cable pulling machinery and adequate communication equipment along the 620m long section of the tunnel system area, in order to prevent any damage to the cables running through multiple depths, and over metallic steel structural supports.
Fortunately, due to the excellent cable pulling preparation works, the use of very skilled manpower and the continuous supervision, no any damages were observed.
CEPCO extends its thanks and appreciations to the Saudi Electricity Company (SEC) management namely:
• Engr. Mahdi Nasser Al Dossari – CEO PDC Company
• Engr. Mohammad Ibrahim Al Omar – VP Projects
• Engr. Mohammad Mannan – PDC Western Area Portfolio Manager
• Engr. Abdulla Al Sehli – North West Projects Program Manager
• Engr. Mohammad Ibrahim Attar – Group Leader
• SEC West Project Managers and Supervision Engineers.
