Device For Cooling Electric Machines, Particularly Turbogenerators

Abstract

To cool turbogenerators having water-cooled stator and rotor windings and a cooling-water connecting head at the end of the rotor shaft, an intermediate tank containing a gas cushion maintained at a pressure slightly higher than atmospheric is interposed between a main water tank that is at elevated pressure and a water chamber that is at reduced pressure and is located adjacent a cooling-water discharge chamber. Water accumulating in the intermediate tank is fed back to the main water tank by a booster pump.

Description

The invention of the instant application relates to a device for cooling electric machines, particularly turbogenerators, and more specifically to such machines having water-cooled stator and rotor windings. Such a cooling device is known, for example, from German Published Non-prosecuted Pat. Application DOS 2 016 169. In this heretofore known device, a cooling-water connecting head is mounted on the end of the rotor shaft, and includes a shaft pump driven by the shaft as well as cooling-water input and output chambers. Moreover, in the circulatory loop between the cooling-water chambers, there is connected a water tank which is subjected to a cushion of gas acting at elevated pressure.

The following problems generally arise with a cooling-water circulation system of this heretofore known type: first, the pump should have a self-contained drive, which is generally achieved by directly coupling the pump to the rotor. In addition, attention must be given to operating the cooling-water pump with minimal cavitation. Wear due to cavitation at the intake of the shaft pump increases, however, with increasing rotary speed and increasing water flow rate. In order to avoid excessive wear due to cavitation at the pump, an initial or prior pressure is required in the suction line, which can be 3 to 4 atmg (atmospheres excess pressure), depending upon the operating rotary speed and the water flow rate. This pressure is usually generated by a gas cushion introduced into the water tank. This entire gas cushion pressure, however, also acts on the outermost water chamber at the cooling-water connecting head that faces toward atmosphere, so that an undesirably high pressure occurs at the shaft seal.

To seal the shaft, a maintenance-free and wear-resistant seal that fulfills the requirement for turbogenerator design of a running time of at least 20,000 hours without stopping, is accordingly necessary. Contact-free slotted or split sleeve seals or labyrinth-type seals have been found to be most reliable and suitable, as they are also least costly from the technical standpoint. With such contact-free slotted or split sleeve seals, continuous water-leakage on the air side is unavoidable. This water leakage should, however, be kept as low as possible. Since this leakage water is chemically pure and accordingly has low electrical conductivity, the recovery or reclamation thereof in the course of continuous operation cannot be disregarded. This leakage water becomes enriched with oxygen, however, when in contact with air, which can cause corrosion in the conventionally hollow lines or passages located in the rotor and stator windings. Consequently, the leakage water is conducted through a collecting tank and over a palladium catalyzer wherein the oxygen entrained by the leakage water combines with the hydrogen therein to form additional water which is then returned to the main water tank. The necessity for keeping the water leakage as low as possible is dictated by the fact that the size of the ultra-expensive palladium catalyzer increases in proportion to the water flow rate.

It is accordingly an object of the invention to provide a device for cooling electric machines which has a cooling-water circulatory system with a water connecting head that has the least possible water leakage. Since the required suction pressure and, accordingly, the starting or prior pressure in the water tank must be maintained, on the one hand, for operating the pump with minimal cavitation, while, on the other hand, the amount of water leakage is dependent upon the pressure in the end-most water chamber at the air side, a further object of the invention is to provide means for markedly reducing this pressure without, however, sacrificing the integrity of the closed circulatory loop.

With the foregoing and other objects in view, there is provided in accordance with the invention, a device for cooling electric machines, particularly turbogenerators, having a rotor mounted on a shaft and water-cooled stator and rotor windings, comprising a cooling-water connecting head located at an end of the rotor shaft and having a cooling-water inlet chamber and a cooling-water outlet chamber, circulatory means interconnecting the inlet and outlet chambers, an external water tank connected in the circulatory means between the inlet and outlet chambers, means for maintaining a gas cushion at elevated pressure within the external water tank, a pressure-reducing water chamber located adjacent and communicating with the outlet chamber, an intermediate tank connected between the pressure-reducing water chamber and the external water tank and having an air cushion therein at a pressure slightly higher than atmospheric pressure, and booster pump means connected between the intermediate tank and the external water tank for recirculating water accumulating in the intermediate tank to the external water tank.

By means of this provision of an intermediate tank and the pressure-reducing effect thereof at the end-most sealing location of the cooling-water connecting head, the water leakage occurring at the air side of the connecting head is reduced to a minimum. Accordingly, it is possible also to employ a slotted or split sleeve seal at this location independently of the output of the machine and the operating rotary speed thereof. Due to this pressure reduction in the end-most water chamber of the connecting head, the sealing problems, which would have otherwise been difficult to solve and which result from the aforementioned lengthy running periods and from the axial expansion of the rotor shaft of about 60 mm or more for large machines, are greatly reduced.

In accordance with another feature of the invention, and in order to maintain a predetermined pressure of the gas cushion in the intermediate tank, means are provided connecting the external water tank and the intermediate tank so as to afford communication between the respective gas cushions therein, a safety valve being connected in the connecting means between the external water tank and the intermediate tank. In accordance with yet another feature of the invention, a safety valve is connected to the intermediate tank.

Tapped water escaping nevertheless from the pressure-reducing water chamber can be withdrawn in a conventional manner from a further chamber located, in accordance with yet another feature of the invention, adjacent the pressure-reducing water chamber and having a pair of opposite walls having respective ends, between which and the rotor shaft, shaft sealing means are interposed, the shaft sealing means admitting into the further chamber atmospheric air in addition to the tapped water. The tapped water withdrawn from the further chamber is then recirculated to the external water tank through circuit means connecting the further chamber with the external water tank and including a collecting tank, a pump and oxygen-removing catalyzer means connected therein.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in device for cooling electric machines, particularly turbogenerators, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the single FIGURE of the drawing which is a diagrammatic view of the device for cooling electric machines in accordance with the invention, schematically showing the circulatory system for cooling water and the cooling-water connecting head.

Referring now to the drawing FIGURE, there is shown therein a central cooling-water tank 1 wherein an initial or prior pressure of about 3 atmg is maintained by a gas cushion 2. Cooling water flows from the central or main tank 1 through a suction line 3 into an inlet or suction chamber 4 formed in a coolant-water connecting head 5. The cooling water is fed from the inlet chamber 4 by a shaft pump 7, which is mounted on the shaft 6 of an otherwise unillustrated electric machine such as a turbogenerator, through a line 8 and a cooler 9 to the schematically shown stator winding 10 of the machine and to an axial bore 11 formed in the shaft 6 of the machine rotor for cooling the schematically shown rotor winding 12. The warmed cooling water then flows back from the stator winding 10 through a line 13 directly to the external water tank 1 and from the cooling-water outlet chamber 14 in the cooling-water connecting head 5 out of the rotor and through a line 15 into the external water tank 1. The pressure in the cooling-water outlet chamber 14 is about 3.5 atmg, so that this pressure also prevails at the slotted or split sleeve or labyrinth seal 16 between the outlet chamber 14 and an adjacent chamber 17. In accordance with the invention, the adjacent chamber 17 is connected by a line 18 with an intermediate tank 19 wherein a pressure slightly above atmospheric pressure is maintained by a gas cushion 20, the pressure in the adjacent chamber 17 being from 350 mm water column to about 0.2 atmg. In the additional adjacent chamber 17, there prevails a pressure of 0.25 to about 0.4 atmg only, which is also simultaneously applied to the slotted or split sleeve seal 21 located at an end of the wall disposed between the water chamber 17 and the next-succeeding chamber 22. Due to this pressure reduction, the greatest part of the leakage water discharged from the cooling-water outlet chamber 14 is delivered to the intermediate tank 19, without having any connection to atmosphere, and only a relatively small quantity of leakage water flows into the leakage water chamber 22 which is partly filled with air and partly with hydrogen separated from the water. The pressure of the gas cushion 20 can then, in accordance with the invention, be adjusted without regard to any other matters so that, on the one hand, a minimal quantity of leakage water is obtained while, on the other hand, however, a breakthrough of air from the chamber 22 through the slotted or split sleeve seal 21 into the pressure-reducing adjacent chamber 17 under all operating conditions is avoided. The leakage water then flows in conventional manner into a lower lying collecting tank 23 and is pumped back into the external water tank through a palladium catalyzer 26, regulated with the aid of a water level control 24 and a return flow pump 25. The quantity of tapped water flowing into the intermediate tank 19 is also regulated by a water level control 27 and is returned to the main water tank 1 with the aid of a booster or pressure-raising pump 28. The gas cushion 2 formed in the main water tank 1 through a hydrogen supply line 29 and a pressure-reduction valve 30 is connected through another pressure-reduction valve 31 with the gas cushion 20 formed in the intermediate tank 19. In addition, a safety valve 32 set to 0.1 to 0.2 atmg ensures that the gas cushion pressure is not exceeded in the intermediate tank 19.

Accordingly, in a relatively simple manner, the aforedescribed device of the invention assures reliably and economically, that only a very small amount of leakage water escapes from the cooling-water connecting head and is mixed with entering air. Moreover, due to the consequent pressure reduction, relatively simple slotted or split sleeve or labyrinth seals can be employed at all sealing locations.

Claims

We claim:

1. In a system for cooling electric machines of the type having a rotor mounted on a shaft and water-cooled stator and rotor windings, comprising a cooling-water connecting head located at an end of the rotor shaft and having a cooling-water inlet chamber and a cooling-water outlet chamber, circulatory means interconnecting said inlet and outlet chambers, an external water tank connected in said circulatory means between said inlet and outlet chambers, and means for maintaining a gas cushion at elevated pressure within said external water tank: a pressure-reducing water chamber located adjacent and communicating with said outlet chamber, an intermediate tank connected between said pressure-reducing water chamber and said external water tank and having an air cushion therein at a pressure slightly higher than atmospheric pressure, and booster pump means connected between said intermediate tank and said external water tank for recirculating water accumulating in said intermediate tank to said external water tank.

2. Device according to claim 1 including means connecting said external water tank and said intermediate tank so as to afford communication between the respective gas cushions therein, and a pressure-reducing valve connected in said connecting means between said external water tank and said intermediate tank.

3. Device according to claim 1 including a safety valve connected to said intermediate tank.

4. Device according to claim 1 including water-level control means for regulating outflow of water accumulated in said intermediate tank to said external water tank.

5. Device according to claim 1 including a further chamber adjacent said pressure-reducing water chamber and having a pair of opposite walls, shaft sealing means disposed between respective ends of said walls and the rotor shaft and being adapted to admit atmospheric air and water tapped from said outlet chamber into said further chamber, and circuit means connecting said further chamber and said external water tank for recirculating the tapped water received in said further chamber to said external water tank, said circuit means including a collecting tank, a pump and oxygen-removing catalyzer means connected therein.