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Transmission Systems: Mexico in the fast lane

Joel Duvert, a project manager within Alstom’s Transmission and Distribution sector, explains how fast-track turnkey transmission projects are transforming the Mexican national grid.

Mexico is the throes of massively boosting its electrical generation and transmission capacity. Since 2000, state-owned utility Comision Federal de Electricidad (CFE) has increased generation capacity by 5418 MW to 40 341 MW in response to an annual increase in consumption of over five per cent.

The Sabino substation was the most challenging of the whole project, because of its size, the difficulties of the terrain and its remoteness
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Accompanying this explosion in generation has been a commensurate increase in transmission capacity, with a massive 60 per cent increase in the number of transmission and distribution substations over the past 12 years.

The scale and speed of the country’s infrastructure development is impressive, and contractors have had to pull out all the stops to meet the demanding deadlines. One such contractor, Alstom, has just completed two turnkey projects worth $54 million on time in Mexico.

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The contract for the first, the 410 National System project, was signed on May 23, 2001 between CFE and a consortium consisting of Alstom’s Transmission and Distribution (T&D) sector in Mexico, leader of the consortium, and Spanish firms Abengoa and Elecnor. The consortium was engaged to build 17 turnkey substations of 115 kV, 230 kV, and 400 kV, all to be completed within 18 months. The substations were to be located in 12 different states of Mexico. The total value of the contract was $173 million.

Challenging projects

Alstom’s share of that project, for a total contract value of $46.5 million, comprised the extension of the 230/115 kV substation of Silao in the state of Guanajuato, 350 km north-west of Mexico City, and the construction of two new 400/115 kV substations, at San Martin near the town of Puebla, 120 km east of the capital, and Sabino, in the state of Chiapas in the south of the country.

The Sabino substation was the most challenging of the whole project, because of its size ” it was the biggest of the project, with eight bays and a total capacity of 500 MVA ” the difficulties of the terrain and its remoteness, 1200 km from Mexico City in the very poor State of Chiapas, which lacks all the infrastructure for such a project.

The State of Chiapas provides around 60 per cent of Mexico’s electricity, being rich in hydroelectric resources. The Sabino substation is a distribution node, converting the 400 kV supply to 115 kV and despatching it via seven different feeders to distribution substations. Feeding the substation are an existing 400 kV line, which makes up part of the national grid, and a new 400 kV line bringing power from the newly built Chicoasen hydroelectric plant 15 km away.

The contract was a turnkey one, which means that CFE provided the land and the basic design of the substation, and Alstom delivered the complete substation 18 months later. Starting from an empty field, Alstom had first to assess the site conditions and transform the client’s basic one-line diagram into a plan for a complete substation. The full design produced took into account the terrain, the seismic conditions and factors such as wind speeds, which in the case of Sabino were significant, as up to 225 km/h wind speeds can be experienced in the area during the hurricane season. The detailed substation design work, carried out by Alstom civil and electrical engineers, was a significant part of the project, and amounted to 12 000 man hours at Sabino.

The very rocky land assigned by the client for the building of the substation created difficulties in terms of civil engineering and civil works. Part of the land was relatively flat, but the southern part contained a rocky hill. To create a flat platform, the team had to cut away 15 m of rock to remove the hill and remove 2 m depth of rock from over 40 per cent of the 16 ha site to flatten it out. In addition, the team had to fill in a gully on another part of the site.

This resulted in an important delay in the completion of the civil works that was later recovered ” in spite of adverse weather conditions during the rainy season ” by the application of a rush programme for erection works and precommissioning tests.

All the substation equipment, such as circuit breakers, disconnecting switches, current transformers, potential transformers, power transformers, surge arresters and physical structures to support the equipment was procured and installed by Alstom, much of it also manufactured by the company in plants across the globe. The SCADA control system was connected to regional dispatch centres, and is thus remotely operated by CFE.

The testing of the substation was carried out in three stages. Firstly, individual components were tested in the factory, and secondly, tested in the field in the precommissioning phase to make sure that all parts are working. This stage includes the ‘loop’ test, which checks that command signals transmitted from the control centre to field equipment correctly carried out and that field equipment signals are by received by the control system. The final stage of testing, the ‘energising’ and commissioning of the substation, was carried out by CFE.

Mexico is attempting to boost power generation and transmission capacity to meet rapidly growing demand
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The second substation to be built was at San Martin, near Puebla, 120 km east of Mexico City. The town is heavily industrialized and the substation was needed to reinforce the distribution grid in the area. The substation transforms 230 kV down to 115 kV, but in this case Alstom built only half of the substation, the 230 kV section and the connection with an existing 230 kV line from the national grid into the substation to provide extra power to the region. Another contractor, Isolux, built the 115 kV part of the substation. Design work on this project totalled 5000 hours for Alstom.

The final work in project 410 for Alstom was the extension of the 230/115 kV substation of Silao in the state of Guanajuato, 350 km north-west of Mexico City. The town is in the Bajio region of Mexico, home to industrial towns such as Leon. The extension was needed to convert 230 kV power to feed two 115 kV lines to local towns to beef up distribution in the area.

Eventually, all three substations were successfully completed and delivered to the client, on the contractual date for the new substations of San Martin and Sabino and two weeks ahead of schedule for the extension of the Silao substation.

Tres Estrellas extension

The $7.6 million contract for the second project for the CFE was signed on January 17, 2002 with CYMI, the Mexican branch of the Spanish company Grupo Dragados. It subcontracted to Alstom T&D in Mexico the construction, on a turnkey basis, of the extension of the Tres Estrellas 400 kV substation in the state of Veracruz, in order to link the new Tuxpan III power station to the national grid.

The construction of two additional bays came just five months after Alstom’s completion of the construction of the first phase of the substation in September 2001, after a gruelling tight schedule of only ten months. This gave the company a headstart in terms of knowing the terrain and local conditions. The soil in this swampy area has the consistency of chewing gum, and work began immediately to replace it with a more workable soil. Alstom completed the new project within the same very tight ten-month time schedule and the substation was commissioned on November 17, 2002 as per the contractual completion date.

Meeting needs

Electricity consumption in Mexico is predicted to continue to increase at an average rate of 5.6 per cent per annum until 2011, and CFE plans to continue its programme of infrastructure investment to meet this need. By December 2011, CFE will have put into service a further 61 new power stations, providing 28 862 MW of power. Alongside this, CFE plans to build new transmission lines and increase the capacity of others.

Alstom and its partners have built 17 turnkey substations of 115 kV, 230 kV, and 400 kV in 12 different states
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Such a staggering increase in capacity in such a short space of time will no doubt prompt more such fast-track turnkey transmission projects in Mexico in the coming years.