At the start of the year GUGLER Water Turbines GmbH from Austria successfully completed its first project in Vietnam with the commissioning of the completely revised Nam Tha 4 power plant.

The powerhouse of the operator Phuc Khanh Energy Development and Construction Investment JSC had been badly affected by a flood and was newly fitted out with state-of-the-art technology by the engineers from Upper Austria. At its core, the contract comprised two identically designed Francis spiral turbines with directly coupled synchronous generators as well as the associated hydraulic equipment and inlet valves. At full load, the new machines produce a maximum output of more than 17.4 MW, and the electricity which is generated is fed into the public power grid. Thanks to the new equipment, both the operational reliability and the efficiency of the plant were increased significantly.

In Vietnam, a country with a population of around 90 million people, hydropower generation is one of the most important pillars of the country‘s electricity supply. Over a third of the electricity generated in the country is obtained from the renewable resource of water, with the rest of the electricity being produced primarily from coal, natural gas or nuclear power. With hydropower potential of around 120,000 GWh each year – less than half of which is utilised to produce energy today – Vietnam is one of the most interesting markets for hydropower in South-East Asia. Some of the most efficient plants can be found in northern Vietnam on the Red River. This originates in neighbouring China and, passing through the capital city of Hanoi down to its mouth feeding into the Gulf of Tonkin, it forms one of the main waterways in this coastal state. Over the years, a whole series of hydropower plants of different designs and power classes have also been constructed on the numerous tributaries of this major river.

POWERHOUSE RAVAGED
One of the tributaries of the Red River that has been most heavily utilised for hydropower in the recent past is the Nam Tha in the north-western province of Lào Cai. The Nam Tha 4 power plant, which is designed as a discharge plant and is run by the operator Phuc Khanh Energy Development and Construction Investment in the mountainous district of Văn Bàn, only started operating around four years ago. However, power generation came to an abrupt end after just a comparatively short period of time. A devastating storm during the rainy season in 2018 caused widespread flooding in the region which also affected the Nam Tha 4 power plant. The upstream storage reservoir for the plant was unable to cope with the vast quantities of rainfall, which caused the body of water to slosh over the concrete dam with immense force. This then caused serious damage to the power plant infrastructure. For example, some sections of the underground penstock were completely destroyed by the masses of water. The impact was even worse on the powerhouse, whose basement and ground floor was flooded and covered in mud. The sensitive electromechanical equipment was so badly affected by the huge quantities of water and mud that getting the plant back up and running quickly was out of the question.

AMBITIOUS TIMETABLE
To get the power plant connected to the grid again as quickly as possible, the operating company commissioned the Vietnamese project developer and automation specialist Ocean Industry Corporation (OCI) to completely revitalise the plant. As part of the tender that was drawn up by OCI, the Austrian company GUGLER Water Turbines GmbH was able to secure the contract to supply the two turbines and the associated equipment. For the turbine manufacturer that operates internationally and can cite a large number of reference projects in South-East Asia in particular, the project was the first order it had received in Vietnam. GUGLER project manager Roland Fleischmann points out that the timeframe for the contract was extremely tight: “Usually a project of this magnitude takes around a year. But as the plant could not be out of operation for too long following the total failure and the power generation losses associated with this, the engineering, production and installation of all the equipment had to be completed in the space of just eight months.”

COMPLEXITY REDUCED
To be able to meet the ambitious timetable, GUGLER started engineering the turbines as soon as the contract was signed at the beginning of 2019. According to Fleischmann, one of the key challenges of the project was adapting the new turbines to the existing infrastructure at the plant. Among other things, this related to the design of the two identically configured Francis spiral turbines. Owing to the existing route of the penstock, the inlet of the spiral turbines had to be desig­ned to be at an angle at the bottom, which in turn required special apparatus for installation. In addition, the designers placed great importance on coming up with a design for the turbines and the associated infrastructure that was as simple and easy to maintain as possible. “Essentially the complete revitalisation made the plant less complex and susceptible to faults. We installed our tried-and-tested cooling system in place of the bearing cooling system which previously featured separate units, pumps, filters and a vast quantity of lines and cables. In principle, our system is a closed-loop cooling circuit which uses heat exchangers installed in the tailwater to keep the oil used to lubricate the generator bearings at the optimum temperature,” explains Fleischmann, adding that the spiral housings of the turbines were provided with a special zinc-based protective coating (ZINGA system) to protect them from the water containing lots of sediment.

BOOST IN PERFORMANCE
Following the factory acceptance test at the end of July 2019, the turbines, which were manufactured at a Slovenian partner company, were ready to make the journey to Vietnam. To make installation on site as straightforward as possible, the guide vane mechanisms were already installed and preset at the factory. Including the obligatory customs formalities, the journey by sea and land to north-western Vietnam took around two months. Once the turbines arrived at the construction site, work to install the hydroelectric equipment began in October of last year. The installation work was carried out by local specialists under the guidance of a GUGLER supervisor. The client OCI provided all the electrical and control engineering equipment. A new indoor crane was erected in the powerhouse to install the synchronous generators from the Spanish manufacturer GAMESA ELECTRIC, each weighing around 40 tonnes. The generators and turbines, which each have a horizontal axis, were directly coupled together, which meant that separate turbine bearings were not required. The forces which are produced on the runners by the rotation are absorbed by the oil-cooled bearings of the generators. To ensure that the used air from the air-cooled generators does not contribute to undesired heating of the powerhouse, it is discharged into the open air via a concrete shaft. When operating at full flow rate, each of the highly efficient turbines can utilise an extraction water quantity of 4.9 m³/s, with a gross drop of 194 m available. At full load, each of the turbines rotating at 1,000 rpm produces a bottleneck output of 8,734 kW. Thanks to the two turbines, the plant is ideally equipped to operate both at full load and at partial load. As an annual average, the turbine utilisation (plant factor) is around 60 percent, and at peak times the machines can even be operated with an output of 110 percent. The power which is generated is fed via an overhead transmission line directly into the public power grid, and the annual standard capacity of the power plant is around 47 GWh on aver­age.

FURTHER PROJECTS BEING IMPLEMENTED
Following the smooth fitting and the final electrical engineering installation work, the fully revitalised Nam Tha 4 power plant be­gan operating again in January of this year. Fleischmann points out that the efficiency of the plant has been significantly improved by its complete renewal. “The old turbine units never delivered the performance that was calculated by the operator even when operating at full flow, and their function was also compromised by persistent vibrations. Our turbines now work perfectly and achieve maximum levels of efficiency in all operating conditions and at all flow rates. The Nam Tha 4 power plant was the first GUGLER project in Vietnam; other assignments in the country are currently in the implementation phase. With this excellent reference, we are very confident that we will also be able to fit out more power plants in Vietnam in the future.”