On the Necaxa River

How Mexico's largest hydroelectric power plant was built 

Siemens has been active in Mexico since the end of the 19th century. In 1897, the German electrical engineering company built a steam power plant for Mexico City and installed the Mexican capital's entire electric lighting system. Six years later, Siemens played a major role in the construction of Mexico’s highest-capacity and most important hydroelectric plant. The huge project on the Necaxa River was carried out under a contract awarded by the Mexican Light and Power Compagnie Ltd. of Canada. 

In operation for more than 100 years – An early investment in the country’s future

Mexico grasped the importance of hydropower for the country at an early stage and seized the opportunity to transport the locally generated electricity through high-voltage lines to consumers in major cities. Construction of Mexico’s highest-capacity and most important hydroelectric plant began in 1903 along the Necaxa River. The customer was Mexican Light and Power Compagnie Ltd. of Montreal, Canada. The plant would provide power to Mexico City, located 150 kilometers away, and to gold mines in El Oro located an additional 120 kilometers away. Siemens-Schuckertwerke served as the general contractor and supplier of the electrical systems. 

A huge step toward the modern age – Power and light for Mexico City 

By this time, Siemens had already gained some experience with Mexican customers: In 1897, Siemens & Halske built a steam power plant for Mexico City and installed the entire electric lighting system there. During the latter project, the city’s gas and electric lighting system was replaced with 800 lamps. It was one of the world’s largest projects at the time.



More than 160 kilometers of cable and 185 kilometers of overhead cable were laid. Despite the tremendous work involved, Siemens completed the power plant and lighting system in just 10 months. 

A location with many challenges – Complex construction work on the Necaxa River 

By contrast, the planned location of the new power plant on the Necaxa River was very remote – a huge amount of preparatory work had to be done before the actual construction project could begin: 


Roads and railways had to be built to carry construction materials and electrical equipment to the site. Nearly 50 kilometers of track had to be laid. Three towns were established as part of the project in order to provide homes for residents of villages later flooded by the dam.


Housing also had to be provided for about 4,000 workers at the main construction site. But these were hardly the only problems that arose:  


All machine parts, construction equipment and other material had to be lowered down a cliff to the construction site on a special elevator. Even a temporary power plant was built to provide electricity for the construction project.

The path of water – An ingenious system

First the water of the Tenango River was dammed up and then channeled through a nearly 1-kilometer-long tunnel to the Necaxa. Several reservoirs along the way served to manage the water supply. Due to the high risk of earthquakes in the region, these reservoirs were retained not by walls of masonry or concrete, but by an earthen dam. A final 45-million-cubic-meter reservoir held water that then plunged 442 meters through two large pipes to run the plant turbines. 


The six vertical turbines were coupled directly to three-phase generators to avoid the friction losses that could be caused by mechanical transmissions. The rotor rings and rotors for the Siemens generators had to be built in segments so they could be transported from Europe to Mexico. Three single-phase alternating current transformers for each generator converted the generator’s 4,000 volts to 60,000 volts for transmission.


To transmit the electricity from the Necaxa to Mexico City and onward to El Oro, General Electric built a 60,000-volt power line with the associated substations and switchgears. At the receiving end, substations converted the electricity to the voltage required by the respective end user.


The work on Mexico’s largest hydroelectric plant was completed in 1905. 


On December 3 of that year, Mexican President Porfirio Díaz looked on as the plant went into operation. The power plant is still producing electricity today.



Dr. Franz Hebestreit 

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Further information on this topic

Further reading

  • Gerhart Jacob-Wendler: Deutsche Elektroindustrie in Lateinamerika. Siemens und AEG, 1890–1914, Stuttgart 1982 [German only]
  • F.S. Pearson / P.O. Blackwell, The Necaxa Plant of the Mexican Light and Power Company, in: Transactions of the American Society of Civil Engineers, Vol. LVIII, June 1907, pp. 37–50