Hydraulic solution for Mexican dam

Hydraulic solution for Mexican dam
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July 2016

 

At the Mexican Malpaso Dam, Bosch Rexroth engineers replace worn out electromechanical drives on the spillway gates. The hydraulic solution is a blueprint for the future retrofitting of dams.

A crane with a huge iron plate on its hook stands on the dam wall at Nezahualcóyotl Lake in southern Mexico. The crane operator carefully lowers it into the lake in front of a spillway gate in the dam. The water masses push the plate against the concrete wall as it slowly sinks down, closing the opening. The spillway gate then opens and the water between it and the iron plate drains off. The way is now clear for the Bosch Rexroth employees: The spillway gate, which usually prevents the dam from overflowing, is now dry. Manuel Schuhmann, technical project manager at Bosch Rexroth, is enthusiastic: “It is fascinating: The plate, or the so-called stop lock, is held in place solely by the reservoir’s water pressure.” The task of the engineers is to modernize the old drives on the dam’s spillway gates.

Cautious innovation

Built between 1958 and 1966, the 138-meter-high dam, which is officially known as the Nezahualcóyotl Dam, holds back a lake with more than 10 million cubic meters of water and a surface area of around 110 square kilometers. On the one hand, the construction protects the lowlands of the Federal State of Tabasco against yearly flooding, and on the other hand, six Francis turbines in the dam generate sustainable energy for the region. The Comisión Federal de Electricidad (CFE) operates the dam and invests regularly in the safety and availability of all its technical equipment. In 2015, the drives of three out of a total of seven spillway gates, which regulate the water level of the reservoir, were to be modernized: Each spillway had an electric motor driving two pinion gear drives via a mechanical shaft. The motor had been raising the 170-ton spillway gate using chains on each side – and that since the dam went into operation in the 1960s. Martín Gómez, project manager at Bosch Rexroth in Mexico, recalls the CFE’s invitation to tender for this project: “We initially proposed a solution with long-travel hydraulic cylinders as a drive for the gates.” The team that also includes Hector Vazquez and Hector De Reza had already frequently used this proven type of drive in new constructions, such as the La Yesca Dam, which is also in Mexico. However, the concrete structure at the Malpaso Dam proved to be unsuitable. Without reinforcement, the wall would not have been able to withstand the forces of the cylinders. And converting the concrete structure would have been a lengthy and complex process. “So we developed a solution that uses the existing chain hoist, but with all the advantages of hydraulics.” His colleague Schuhmann adds: “In steel construction for hydraulic engineering, the most important factor is safety. When we were able to show that similar hydraulic systems were already being successfully used in other dams, we got the contract.”

Bosch Rexroth employees Manuel Schuhmann, Martín Gómez und Abraham Huerta (from left) pose in front of the modernized spillway gates. Magnifier

Bosch Rexroth employees Manuel Schuhmann, Martín Gómez und Abraham Huerta (from left) pose in front of the modernized spillway gates.

 
A Hägglunds radial piston motor drives the chain directly. The soft startup of the motor significantly extends the service life of the chain. Magnifier

A Hägglunds radial piston motor drives the chain directly. The soft startup of the motor significantly extends the service life of the chain.

Hydraulic units on the dam: The housings are air-conditioned and protect the system against the tropical weather. Magnifier

Hydraulic units on the dam: The housings are air-conditioned and protect the system against the tropical weather.

 

Really safe

The Malpaso solution has a hydraulic unit permanently installed in each gate, which drives two slow-running heavy-duty radial piston engines. These Hägglunds motors from Rexroth replace the mechanical gear and drive the drive pinions of the chains directly. Gómez explains: “The hydraulic system has natural overload protection. If, for example, a tree trunk gets wedged in the gate and the chain load becomes greater than calculated, a pressure relief valve dissipates the pressure without damaging the drive. This would cause a mechanical drive to break down. Our hydraulic solution offers a clear safety advantage. “In order to further increase safety, the Bosch Rexroth hydraulic engineers mounted a special spring pressure disk brake on each motor, which remains open due to the hydraulic pressure. If the control pressure fails, the brake closes automatically with enough force to stop the spillway. So it can never shut in an uncontrolled manner.

Gentle tension

The new hydraulic drive protects the chains. The electric motor used to be jerky when started, where it yanked and tugged at the chains before moving the spillway. This not only placed a lot of stress on the chain links but also on all the mechanical parts involved, which meant they needed to be serviced frequently. “The hydraulic drive, on the other hand, starts up very slowly and steadily and gently tightens the chain,” says Gómez. “This considerably reduces the maintenance measures required.” Bosch Rexroth not only took over the whole engineering and installation, but also the electrical control system, including software programming. Schuhmann explains: “Each hydraulic unit has its own electrical control system. All three can also be optionally controlled via a panel. The operator can conveniently make adjustments on the touchscreen so that the spillway opens one meter, for example.” Compared with the buttons and levers, this is a huge improvement in ease of use. The decisive factor, however, lies elsewhere: The spillway now transmits data and indicates whether it is closed or to what degree it is open, not to mention the temperature and water pressure. The Bosch Rexroth engineers worked three months with their backs to the reservoir. The retrofit project was completed in June 2015 where the crane lifted out the stoplogs again: Three spillway gates now have a new, safer drive. The remaining four are soon to follow. Schuhmann: “We already have inquiries from India, where they want to know more about the hydraulic chain hoist drive. This could be a new standard solution for retrofits!”