lubrication oil required and the size of the turbine bearing and the generators. T e spectrum of the various projects ranges from 25 l/min to 3,000 l/min at pressures of 3 to 8 bar in the recirculation circuit. T e oil temperature can rise to up to 60°C due to the friction heat in the bearing, which means that pump confi gurations were chosen which are designed for up to 120°C.

COMPLEX DRIVES CONTROL TURBINE PERFORMANCE However, screw pumps are not just used for bearing lubrication, but also for controlling turbine speed. T is permanent control is essential 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

Notos pumps were used in the Brazilian project

Hydroelectric power is booming in Brazil: it has some of the largest hydroelectric power stations in the world

the spirals, the diameter of the spindles and the shape of the spindle profi le. 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 overfl ow valve protects the system against overload.

lubrication oil circulation. T e enormous weight of the turbines that 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 fi lm at all between the rotating and static components. Gear pumps are used for this, which can generate 100 to 250 bar. T is means the moving components of the dry bearing can easily be raised and reliably lubricated. Injection is stopped as soon as a

stable fi lm of oil is established. From this point onwards, the continuous supply of lubricant and the feedback to cooling and fi ltration are taken over by special screw pumps. T ese comprise two spindle- shaped rotors whose helical profi les are exactly attuned to one another and to the housing geometry. T is 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. T e capacity is substantially determined by the incline of

ROBUST PUMP TECHNOLOGY To achieve the longest possible service life and a high level of durability over the whole lifecycle, the screws are made of hardened nitrided 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. In addition, other materials are also available for special usage conditions, for example with chromium oxide or titanium coated screws or pump bodies and bushes made of cast steel, PTFE graphite or aluminium alloys. On the other hand, individual lubrication between the screw and housing is not required, as this is already provided by the conveyed oil. As well as at Estreito, Netzsch systems

are also in use in many other Brazilian hydroelectric power plants, for example at Santo Antônio and at Jirau on the Rio Madeira. T e pumping capacity of the pumps that have been installed varies from site to site, depending on the volume of

torque on the generator shaft. With the Kaplan turbines fi tted at Estreito,

Jirau and Santo Antônio, the appropriate settings are carried out using adjustable blades on the impeller and on the idler. T ese can be set via hydraulic drives, either making them fl atter or steeper, entirely according to requirements and operating conditions and that then regulates the volume of water hitting the rotor. T is not only determines the quantity of electricity generated; the technology is also needed for the start-up and fast acceleration of the turbine. Netzsch do Brasil designed and supplied a complex speed regulation system for this, including a control unit. Lubricant oil according to ISO VG 68 is used as a hydraulic fl uid and this is channelled into the drives on the blades and returned by screw pumps. T e pumps involve a model with three screws, one of which functions as a drive spindle. A three-phase motor is connected and this spindle transmits the power of the motor to the two auxiliary spindles. T e pressure of 68 bar that this generates is suffi cient for precise adjustment of the huge turbine blades while they are running. In this way every variation in speed that is recorded by the regulator can be compensated via the servo-unit by correcting the position of the blades.

Michael Groth is with Netzsch 35

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