Utilities Middle East went along to watch Qatar install its first 400kv transmission line.
Few can fail to notice the cable drums standing proud on the road sides through out Doha. Across the Qatari capital numerous cable installations underway to take electricity to the new developments that pop up seemingly over night.
This is a city abuzz with activity and there are trenches and diggers at every turn. But one project by its sheer magnitude stands out from the rest: the 400 kv power link being installed by Nexans in consortium with Prysmian.
"This 400 kv project is a 16 km turnkey project for Kahramaa [Qatar General Electricity and Water Corp.] and it is the first time a 400 kv cable is being installed in Qatar," explains project manager Laure Tavernier.
The installation forms part of phase 7 of Kahramaa's power transmission system expansion programme. The transmission line will link super substations at Dukhan Road and Al Wajbah and will replace pylons that already line much of the route.
Three cable circuits each comprising three phases are being installed along the 16 km route between the two substations. Nexans is responsible for laying two of the three circuits and is leading the project. The total contract value is Qatar riyal 641 million (US $176 million).
Planning & preparation
In November 2006, the letter of award was signed by all parties involved and the project kicked off, with Nexans and Prysmian agreeing to complete the installation with 18 months.
"Immediately after a contract is signed we mobilise our team to start the engineering and design. We have two main tasks: the design of the cables and accessories and the planning of the route," says Nexans' Hubert Lerebours. The engineering and design phase can take up to six months, but it is this attention to detail that Nexans says lies behind the success of a project.
"We place a lot of emphasis on engineering phase so there will be no surprises or hold-ups later on, such as a cable being too short or too long," he continues.
"In the high-voltage business you manufacture the cables according to the client's specification for each section of project. If we have 100 m more than what we need on the cable that is pure loss for us and we cannot do afford that with the price of these cables. The specification has to be determined but also the requirements in terms of the length.
When we give the factory the order to start manufacturing the engineering onsite has already been done and we know the route, where the cable will be placed, where the joint bay will be, and the length of each section. Only once this is done can we order the parts from the factory. Each client has his own specifications in terms of design and testing and all this has to be customised for each project and client."
The tender documents always outline a theoretical route, but it is down to the company installing the cables to confirm its feasibility and to obtain all necessary permits.
"All countries have planning authorities to define planning the route and the different corridors for the services that have to be installed. So the first step is to receive from the client the tentative cable route, to look at the routing they propose and to submit this routing to the different authorities and this takes around 6 months," says Lerebours.
"At the same time that we apply for authorisation, they tell us where other services are so we can avoid them, for example all the services running parallel or crossing our cable route."
For this project permits had to be obtained from the water, telecoms, roads authorities, the urban planning department and from Qatar petroleum.
Once all the authorisation and documentation has been received the project team draws up a preliminary route, which is then verified using trial pits.
"We perform trial pits on each location where we cross existing services and also at the theoretical joint bay positions to cross check that it is really free of services," says Lerebours. A trial pit typically measures 3 m by 50 cm.
The number of trial excavations depends on where the cable is being routed: in a congested area one might be dug every, whereas in the open desert one pit every 100-150 m might suffice.
"We use the trial pits to confirm the services that are supposed to be there are there and in the right position, as per the drawing and also that where is supposed to be nothing there really is nothing and we can put our cable in.
If there is any mismatch, say if a service that is supposed to be in the position of our trial pit is not there, then we extend it further to find where it really has been laid," he continues.