With the construction of a new hydroelectric power plant, one of the main drinking water supply lines of the Iranian metropolis of Qom (Ghom) has been given an additional energy economy usage.

The project was commissioned by the Iranian “Roshd Sanat Co.”, a company that is primarily active in the energy, industrial and construction sectors. The order for the electromechanical implementation of the project was secured by the Austrian-based hydroelectric power specialist Geppert GmbH at the beginning of 2016. A Francis spiral turbine with a maximum output of nearly 3.5 MW is used as an energy generator. If everything goes as planned, the new power plant should already be generating power from the drinking water mains in only a few months.

The city of Qom is located in northern Iran and is the capital of the province of the same name with around one million inhabitants. The urban area is located around 130 km to the south of the Iranian capital of Tehran and is primarily known as a religious pilgrimage site. Due to the geographical location in an extremely dry region, Qom depends to a great extent on the neighbouring provinces for its water supply. “One of the main drinking water supply lines of the city was rebuilt around 10 years ago. The to-date unused energy potential should be converted into current by a power plant as early as 2017. For purposes of power generation, the drinking water is diverted through a newly built short bypass route with the dimension DN1200 and utilised by a Francis turbine”, is how Geppert project manager Stefan Veiter explains the basic principles of the project still in progress. In addition to the fulfilment of the technical task, the Austrian turbine builder couldn’t avoid a great deal of organisational effort for the official and financial processing. The reason for this is found in the economic sanctions in place against Iran being implemented by the EU. “Because only a few banks in the European region are able to enter into direct financial transactions with Iranian companies, these circumstances resulted in a complicated situation for all parties. An own export approval also had to be applied for with the responsible Austrian federal ministry with regard to the export of the hydroelectric equipment, for example. This procedure ­alone took several months”, is how Veiter ­describes a central aspect of the organisational work involved.

35 KM LONG DRINKING WATER LINE
Due to the enormous length of the drinking water line, extensive water hammer calculations were required, the project manager explains. The reason for this lies in the distance of the power plant control centre from the surge tank, which amounts to around 35 kilometres. With a line diameter of DN1800, the closed pipe system naturally contains a very large quantity of water, which, in the event of an abrupt cut-off procedure, can result in considerable hydraulic forces. In order to avoid damage to the mechanical equipment and the drinking water network, the closing time of the turbine guide vane amounts to approximately 200 seconds, and even 500 seconds for the main inlet valve in front of the machine.

COUNTER PRESSURE REQUIRES A ROBUST DRAFT TUBE
Another special feature of the turbine planned by the Geppert designer Lukas Zingerle involved the layout of the draft tube. Because a permanent counter pressure of approx. 2.5 bar is required on the “underwater side” of the turbine in order to maintain the drinking water supply, the draft tube had to be designed to be correspondingly robust. For the concluding pressure and leakage test, it was ascertained at the factory that the draft tube can also withstand potential water hammer of up to 12 bar undamaged. Veiter emphasises that the important steps of turbine manufacture, such as the production of the Francis runner and the guide vane took place in Gepperts new factory. The entire turbine was manufactured in Austria. Due to its usage in the drinking water system, the Francis runner is entirely made of corrosion-­resistant stainless steel. All interior surfaces of the turbine that come into contact with water were also provided with a food-­compatible special coating.
The plant has a net head of 96 m during normal operation, the water discharge is 4,040 l/s. At full flow the turbine can achieve a maximum output of 3,462 kW. A synchronous generator from the manufacturer GENET coupled directly with the horizontal axis turbine shaft serves as a power transformer. The air-cooled generator, like the turbine, turns at 1,000 RPM and has a connection voltage of 6,300 V, as well as a rated apparent power of 4,500 kVA. The entire generated energy is finally fed into the public power grid.

ELECTRICAL AND PROCESS CONTROL TECHNOLOGY FROM PRO INTEGRIS
Generally high security technology standards had to be taken into account for the electrical technology specifications, Stefan Veiter notes: “In the field of electrical technology, especially for the monitoring and control of turbines, standards must be met which in some cases even exceed the usually high European specifications.” Geppert commissioned the Croatian company PRO INTEGRIS for the implementation of the electrical technology equipment for the power plant. The delivery package includes the turbine governor, relay protection as well as the entire process control technology. The extensive electrical technology “package” on the one hand ensures effective current production, while on the other hand the maintenance of the drinking water supply is of course a high priority. The plant control system is based on a SCADA system and enables both fully automatic and manual operation, as well as the synchronisation with the public power grid. Through the use of the ETHERNET TCP/IP protocol, the control system software is possessed of extensive possibilities for remote control.

REGULAR OPERATION SHOULD START IN AUTUMN
The new power plant should commence operation for the first time in the coming months. The turbine and the electrical technology were just about to be installed at the end of April. Project manager Veiter can nonetheless already come to a positive interim summary: “From a technical perspective, valuable experience could be gathered due to the special circumstances involving the enormously long penstock and the related requirements of the machine. With these basic conditions, we have developed detailed new technical approaches that can be used in future for other projects.” When everything goes as planned, the plant can already start with trial operation in July. The handover to the end customer and the commencement of regular operation is planned for autumn.