ES292502A1 - Hydraulic pumps and reversible pump turbines - Google Patents

Abstract

A hydraulic pump or reversible pumpturbine includes means for suppressing at least partially the circulation of water in the suction tube immediately upstream of the impeller during priming of the pump or of the pumpturbine in operation as a pump, the means including retractable baffles which may be extended in planes transverse to the tangential direction of the suction tube during priming, and retracted during normal operation. Pumping operation of the pump or pump-turbine shown is started by first accelerating the impeller 11, as by means of an auxiliary motor, from rest to synchronous speed in air, the water being depressed down the suction tube 20 by introducing compressed air through a pipe 31 into a space 28 located between sealing rings 29, 30 and communicating with the suction tube through a bore 27 and a cavity 26 in the impeller. During this phase, water may be fed to the impeller seals to prevent seizure. At synchronous speed, the main driving motor is connected to the power supply, e.g. to the grid, and the auxiliary motor may be disconnected. The power absorbed has now risen to about 3 % of full load. Next, the impeller is progressively filled with water, centrifugal effect causing the water to extend progressively inwards from the outer periphery of the impeller. This may be done by gradually exhausting the air from the suction tube 20 through the pipe 31 to allow the water level to rise slowly into the impeller inlet. Alternatively, water is fed from the delivery pipe of the pump into the space between the impeller 11 and adjustable guide vanes 24 (or fixed diffuser vanes 25) and thence inwardly into the impeller. Or, water from the delivery pipe or an extraneous source may be directed in a jet or jets from the suction tube towards the impeller inlet. The inner boundary of the water may thus be brought inwards to substantially the radius of the smallest-diameter part of the front shroud 13, the power absorbed rising to about 10 % of full load in the case of a pump fitted with adjustable guide vanes 24, which are closed. At least by the time this phase is completed, baffles 41 should each be pivoted about a pin 42 by means of a hydraulic jack 43 from the retracted position to the position in which they each extend radially inwards into the suction tube 20. More of the air is then exhausted from the suction tube through the pipe 31, allowing water partially to fill the impeller eye. The power absorbed has now risen to about 17 % of full load for a pump with adjustable guide vanes 24, and to about 40 % for a pump having only fixed diffuser vanes 25. So far, the operation is stable. In the next phase, in which the remaining air is exhausted, the power absorbed rises rapidly at a rate which tends to be difficult to control. By destroying the circumferential component of the vortical flow adjacent the wall of the suction tube 20, the baffles 41 reduce the rate of power rise to an acceptable value, whereby this phase may be spread over a period of 20 seconds instead of a fraction of a second. At the end of this phase, the power absorbed has risen to about 27 % of full load for a pump having adjustable guide vanes 24, or about 60% for a pump having fixed diffuser vanes 25 only. Finally, by gradually opening the guide vanes 24 (or in their absence, a valve in the delivery pipe), the power absorbed is increased to full load. In normal operation, the baffles 41 are retracted.