GB2033092A - Detecting coolant circuit leaks in an electrical machine - Google Patents

Abstract

Leakages in electrical machine windings (3) which are coolant-cooled at least in the stator, are determined by moisture measurement within a closed machine housing (1), in which a cooling gas flow cooled by recooling units (8) is additionally circulated. To produce and maintain a normally stationary moisture state in the gas flow within the machine housing (1), the dew point is fixed by a special heat sink (20, 21) in the region of the cooling gas flow, and then any moisture changes deviating from the stationary state are measured to indicate leakages. In order to distinguish between leakages in the windings (3) and other leakages such as in the units (8), an easily detectable indicator is added to the coolant for the windings (3), and the condensate formed in the heat sink (20,21) is monitored for the possible presence of this indicator. A moisture measuring unit 27 in a gas by pass circuit 26 provides information regarding any leak in either of the two coolant circuits through windings 3 and units 8. <IMAGE>

Description

SPECIFICATION Determining leakages in coolant-cooled dynamoelectrical machine windings The invention relates to determining water leakages in coolant-cooled dynamo-electrical machine windings.

In our British patent application No. 32814/77 there is disclosed a dynamo-electrical machine which is water-cooled at least in the stator. For additional cooling, a circulating cooling gas flow, cooled by recooling units, is maintained within a closed machine housing which encases the rotor and stator windings. To produce and maintain a normally unchanging moisture state in the gas flow within the machine housing, the dew point is fixed by a special heat sink in the region of the cooling gas flow. The flow is then monitored for any moisture variations deviating from the normally unchanging state and any detected moisture changes which may then occur can give unequivocal conclusions regarding the existence of cooling water leakages.Besides detecting cooling water leakages, when this method is used it is also possible to obviate substantially moisture precipitations on endangered machine parts. The leakages which are determinable through moisture changes which occur may take place in the water-cooled windings of the electrical machine, in the water-cooled stator windings or where appropriate in water-cooled rotor windings. In addition to these, the occurrence of leakages in the cooling coils of the recooling units for the cooling gas can also give rise to detectable moisture variations. Thus, information as to the occurrence of a leakage cannot determine whether the detected leakage is due to leakage points in the water-cooled windings or in the recooling units.

The present invention accordingly provides an improvement in the invention of British patent application No. 32814/77.

According to the invention from one aspect there is provided a method of determining leakages in dynamo-electrical machine windings, which are coolant-cooled at least in the stator, by means of moisture measurement within a closed machine housing, which encases the rotor and stator windings and in which additional cooling is provided by a circulating cooling gas flow cooled by recooling units, in which method to maintain a normally unchanging moisture state in the gas flow within the machine housing, the dew point is fixed by a heat sink in the region of the cooling gas flow, any moisture deviations from the normally unchanging state are measured, so as to indicate any leakages in the machine, and the condensate formed in the heat sink is monitored for the possible presence of an indicator added to the coolant for the coolant-cooled windings, whereby to determine whether or not any detected leakage is in the coolant-cooled windings.

According to the invention from a second aspect there is provided a dynamo-electrical machine com prising a closed machine housing which encases the rotor and stator windings of which at least the rotor windings are coolant-cooled, means arranged to maintain a circulating flow of cooling gas within the housing to provide additional cooling, cooling units arranged to cool the circulating flow, a gas drier, including an evaporator, connected so as to be in parallel with the cooling gas flow and arranged to act as a heat sink as the coldest point in the circulating cooling gas flow, so as to fix the dew point and thereby maintain a normally unchanging moisture state within the machine housing, a unit for measuring any moisture deviations frm the normally unchanging state, so as to indicate any leakages in the machine, an indicator feeding-in device connected to the coolant circuitforthe coolant-cooled windings, a condensate collection container connected with the gas drier, and a detector which is situated in the condensate collection container and which is responsive to indicator in the condensate so as to determine whether or not any detected leakage is in the coolant-cooled windings.

For a better understanding of the invention and to show the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing in which the single figure is greatly simplified diagrammative view in longitudinal section, of a dynamo-electrical machine in the form of a generator, with a schematic connection diagram of the cooling arrangements.

As the drawing shows, a stator core 2 with a water-cooled stator winding 3 and also a rotor 4 are arranged in a generator housing 1 which is of pressure-tight and gas-tight construction. The rotor 4 which is driven through the agency of a shaft 5 by a turbine not shown here can also be water-cooled, as will be discussed in more detail at a later stage. For supplementary cooling of the stator core 2 and other machine parts the housing 1 is filled with hydrogen to act as a cooling gas. This cooling gas is circulated by means of fans 6 and 7 arranged on the shaft 5, and recooled in recooling units 8 arranged at the ends of the generator within the housing 1. The flow of cooling gas is indicated by full-line arrows 9 for the recooled gas and by broken-line arrows 10 for the heated branch of the stream of cooling gas.

Two separate cooling water circuits are provided for discharging the heat loss. In the first cooling water circuit, primary water is supplied by a water preparation plant 11 through a supply conduit 12 to a ring main 13 from which the primary water is introduced into the individual hollow conductors of the stator winding 3. At the other side of the stator core 2, the primary water flowing out of the stator winding 3 is conducted by way of a further ring main 14 and an outlet 15 into a cooling water expansion vessel 16 arranged above the housing 1. From this cooling water expansion vessel 16 the primary water is then conducted back through a conduit 17 to the water preparation plant 11, comprising also coolers and pumps not shown here, and from there again recycled to the stator winding 3.In the second cooling water circuit secondary water is conducted through the individual cooling coils to tubing 18 of the coolers 8. As indicated in the drawing, the second cooling water circuit may also be subdivided into several part-circuits. The cooling and preparation of the secondary water are not shown in detail.

So that any leak which may occur within the housing 1 in one of the two cooling water circuits can be detected in good time, an unchanging moisture state for the cooling gas is provided within the housing 1,so that measuring the moisture for ascertaining whether there are leakages of cooling water then gives unequivocal results. For this purpose there is provided within the cooling gas circuit a region in the form of a heat sink, which represents the coldest point of the system and thus defines a specific dew point below which the temperature of other machine parts cannot go in any operating state.For this purpose there is provided in a bypass conduit 19 of the cooling gas circuit a gas drier 20 with an evaporator 21 of conventional construction, in which moisture is precipitated in a well-defined manner and is conducted as condensate 22 by way of a conduit 23 into a condensate collection container 24. This condensate collection container 24 can be emptied from time to time by means of a discharge valve 25, and emptying can be effected automatically, using a suitable level indicating means. In a further bypass conduit 26 relatively to the cooling gas circuit there is arranged a moisture measuring unit 27 with which moisture fluctuations and absolute values can be ascertained.Measuring with the use of the moisture measuring unit 27 moisture changes deviating from the normally unchanged moisture state provides information regarding any leak occurring in either of the two cooling water circuits.

Thus with the use of the moisture measuring arrangement it is possible to determine whether a leak exists. But it does not provide information as to which cooling water circuit a detected leak is located in. But it would be important to have such information, since leaks occurring in the windings have to be taken particularly seriously and could lead to fairly considerable resulting damage.

So that a leak occurring in the first cooling water circuit of the windings can be distuiguished from leaks occurring at another region, the primary water of the first cooling water circuit has an indicator added to it, and the condensate formed in the gas drier 20 is monitored for the possible presence of this indicator. To this end, there is connected to the conduit 17, a feeding-in device 28 by means of which the primary water has added thereto radioactive tritium as an indicator. But it is also possible to introduce the tritium at some other point within the first cooling water circuit. In the event of a leak in the statorwinding 3 the tritium then passes through the cooling gas into the condensate 22 and can be detected there. To detect the tritium, conveniently a scintillator 29, giving a signal indicated by the arrow 30, is arranged in the condensate collection container 24.If a leak is detected by means of the moisture measuring unit 27, this signal 30 gives informaton as to whether tritium is present in the condensate 22 i.e.

whether the leakage ascertained is situated in the first cooling water circuit. If there is no indicator present in the condensate, a detected leakage is to be ascribed to other causes, more particularly leakage points in the recooling units. Thus, the measures described above allow a clear indication as to whether there is a leak in the water-cooled windings of the electrical machine or at another point. Since the causes of the leakage must be known in order to deal in good time with a fault, limit damage or eliminate a defect, knowledge of that kind regarding the origin of the leakage is extremely important.

As already mentioned hereinbefore, the rotor 4 of the generator may also be equipped with a watercooling winding. In this case, from the supply conduit 12 of the primary water some of the primary water is introduced into the shaft 4 by way of a branch conduit 31 and a cooling water connection head 32, and after flowing through the rotor winding is conducted again via the cooling water connection head 32 out from the rotor 4, and introduced by way of a further conduit 33 into the cooling water expansion vessel 16 together with the stator cooling water introduced through the outlet 15. Here again a leak in the winding of the rotor 4 or - as already described - in the statorwinding 3 is indicated by a suitable signal 30 from the scintillator 29.

With the use of radioactive substances as indicators, the scintillator allows also quantitative information regarding the amount of indicator present in the condensate. Then by means of this quantitative information it can also be possible to determine whether in addition to a leak detected in the windings there is a further leak at the same time in some other situation such as, for example, in one of the recooling units.

It is possible to use as indicators substances which can be readily detected chemically or physically.

Thus for example a luminescent colour substance could be used as indicator as described above.

Tritium is particularly suitable as indicator, since it is physiologically unobjectionable in the specific activity involved in this particular use and it can be easily detected even when in very small quantities.

With the help of the described measures it is possible to detect any leaks inside the housing of an electrical machine, indicating separately leakages in the stator winding or the rotor winding which have to be taken particularly seriously. Detecting such leaks at an early stage makes it possible to prevent reliably substantial damage to the machine.

Claims (7)

1. A method of determining leakages in dynamoelectrical windings, which are coolant-cooled at least in the stator, by means of moisture measurement within a closed machine housing, which encases the rotor and statorwindings and in which additional cooling is provided by a circulating cooling gas flow cooled by recooling units, in which method to maintain a normally unchanging moisture state in the gas flow within the machine housing, the dew point is fixed buy a heat sink in the region of the cooling gas flow, any moisture deviations from the normally unchanging state are measured, so as to indicate any leakages in the machine, and the condensate formed in the heat sink is monitored for the possible presence of an indicator added to the coolant for the coolant-cooled windings, whereby to determine whether or not any detected leakage is in the coolant-cooled windings.

2. A method according to claim 1, wherein a radioactive substance is used as indicator.

3. A method according to claim 2, wherein a radioactive isotope in the form of tritium is used as indicator.

4. A method of determining leakages in dynamoelectrical machine windings, substantially as hereinbefore described with reference to the accompanying drawing.

5. A dynamo-electrical machine comprising a closed machine housing which encases the rotor and stator windings of which at least the rotor windings are coolant-cooled, means arranged to maintain a circulating flow of cooling gas within the housing to provide additional cooling, cooling units arranged to cool the circulating flow, a gas drier, including an evaporator, connected so as to be in parallel with the cooling gas flow and arranged to act as a heat sink as the coldest point in the circulating cooling gas flow so as to fix the dew point and thereby maintain a normally unchanging moisture state within the machine housing, a unit for measuring any moisture deviations from the normally unchanging state, so as to indicate any leakages in the machine, an indicator feeding-in device connected to the coolant circuit for the coolant-cooled windings, a condensate collection container connected with the gas drier, and a detector which is situated in the condensate collection container and which is responsive to indicator in the condensate so as to determine whether or not any detected leakage is in the coolant-cooled windings.

6. A dynamo-electrical machine according to claim 5, wherein the detector is a scintillator.

7. A dynamo-electrical machine substantially as hereinbefore described with reference to the accompanying drawing.