Look behind the scenes
Electricity is generated in hydroelectric power plants using turbines. For example the largest Kaplan turbines in the country so far are running at the new Estreito power station on the Rio Tocantins. Their rotor alone weighs 470 tonnes. NETZSCH lubrication systems are being used at Estreito, so as to ensure the turbine support bearings and the guide bearing to the generators run consistently and without any wear or overheating.
In addition to pumps, the systems developed for this also include filters, heat exchangers, instruments, control units and pipes and comprise two essential sub-areas: an injection unit and the actual lubrication oil circulation. The enormous weight of the turbines which rests on the bearings means that the lubricant has to be applied at very high pressure, above all when starting up and switching off, so as to be able to create any lubricating film at all between the rotating and static components. From this point onwards, the continuous supply of lubricant and the feedback to cooling and filtration are taken over by special NOTOS® multi screw pumps. However, multi screw pumps are not just used for bearing lubrication, but also for controlling turbine speed. This permanent control is essential in order to be able to react to changes in the quantity of water in the river being used and it also prevents spinning when there is falling torque on the generator shaft.
NOTOS® multi screw pumps which can generate a high pressure, are used here. These comprise two spindle-shaped rotors whose helical profiles are exactly attuned to one another and to the housing geometry. This means the screws intermesh as they rotate and sealed conveying chambers are formed in which the medium is conveyed from the inlet to the discharge side. The capacity is substantially determined by the incline of the spirals, the diameter of the spindles and the shape of the spindle profile. Due to the hydraulic thrust compensation of the pump, the axial forces here are close to zero even for high pressures. In addition, an integrated spring-loaded overflow valve protects the system against overload. To achieve the longest possible service life and a high level of durability over the whole lifecycle, the screws are made of hardened nitride steel and the pump housing from cast iron. Furthermore, the precise adjustment of the interplay of the spindles is ensured over the long term by special bushes made of bronze.