1、BRITISH STANDARD BS6522:1984 Method for Determination of percentage water saturation of insulating oil UDC 621.315.615.2:665.767:543.812:536.423.45BS6522:1984 This BritishStandard, having been prepared under the directionof the General Electrotechnical Engineering Standards Committee, was published
2、under the authority ofthe Board of BSI and comes intoeffect on 31August1984 BSI 11-1999 The following BSI references relate to the work on this standard: Committee referenceGEL/115 Draft for comment80/29335DC ISBN 0 580 13950 6 Committees responsible for this BritishStandard The preparation of this
3、BritishStandard was entrusted by the General Electrotechnical Engineering Standards Committee (GEL/-) to Technical CommitteeGEL/115 upon which the following bodies were represented: Association of Consulting Engineers Beama Transmission and Distribution Association British Railways Board ERA Technol
4、ogy Ltd. Electricity Supply Industry in England and Wales Institute of Petroleum Institution of Electrical Engineers London Transport Executive The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Lubricants Federation Limited Electric
5、 Cable Makers Confederation Electric Cable Makers Confederation Supertension Cables Group Amendments issued since publication Amd. No. Date of issue CommentsBS6522:1984 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Apparatus 1 4 Sample pr
6、eparation 1 5 Procedure 1 6 Calculation of results 2 7 Precision 2 Figure 1 Arrangement of equipment for the measurement of dew-point 3 Publications referred to Inside back coverBS6522:1984 ii BSI 11-1999 Foreword This BritishStandard has been prepared under the direction of the General Electrotechn
7、ical Engineering Standards Committee. The degradation of cellulosic materials used in oil filled equipment such as transformers is affected by their water content. This can only be estimated from a measurement of the water content of the oil. The presence of water also adversely affects the electric
8、al insulating properties of the oil and cellulose, and it is therefore desirable to maintain the water content at a low level. The determination of absolute water content in insulating oil has in recent years generally been carried out by the Karl Fischer method. This determination requires consider
9、able care and skill and may present additional difficulties if carried out on site. Moreover, the information obtained has to be interpreted in the light of experience; a moderate water content may suggest potential trouble with an unoxidized oil but may be innocuous when found in an oxidized oil. T
10、he method described in this standard determines the percentage saturation of the oil rather than its absolute water content. If the percentage saturation of a sample of oil from a transformer is determined at, say, three temperatures, this will enable a curve to be drawn, using extrapolation if nece
11、ssary, showing the percentage saturation as a function of oil temperature over the range of temperatures found in the oil of that transformer in operation. This immediately reveals whether water condensation is likely, i.e.whether100% saturation may be approached; such conditions may arise at the co
12、ldest regions of the oil, e.g.in the conservator. This information is independent of the age or state of the oil. In addition, since if oil and cellulose are in water equilibrium and at the same temperature their percentage saturations are approximately equal, the curve produced as described above,
13、showing percentage saturation against temperature for the oil, may be regarded as applying also to the paper, etc. in the transformer over the range of temperature found in the paper. While this application to the paper is subject to several sources of error, the indication of paper condition so giv
14、en is much more revealing than can possibly be obtained from an absolute water determination by the Karl Fischer method. NOTEIt has been assumed in the drafting of this BritishStandard that all users of this standard will, if not themselves fully trained, at least be under the supervision of a respo
15、nsible trained person who will be familiar with all normal laboratory practice and engineering practice as appropriate and safety precautions, and that all such precautions will be observed. A British Standard does not purport to include all the necessary provisions of a contract. Users of British S
16、tandards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, an inside back cover and a back cover. This s
17、tandard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6522:1984 BSI 11-1999 1 1 Scope This BritishStandard describes a method of test for the determination of the percentage water saturation o
18、f insulating oil. The method and apparatus described enables the percentage saturations of oil to be determined at temperatures up to60 C provided the dew-point does not exceed ambient temperature. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2
19、 Principle The method relies on the fact that if a volume of air and a volume of oil are in water equilibrium and at the same temperature then their percentage water saturations are equal. In the apparatus described, a small volume of air is circulated through a tubular semi-permeable membrane, imme
20、rsed in a sample of the oil to be examined. After a short time, the air has the same percentage saturation as the oil. The dew-point of the air is measured and converted to percentage saturation; this value is then the percentage saturation of the oil sample with water at that temperature. The oil m
21、ay be heated to obtain percentage saturation at a number of temperatures. 3 Apparatus 3.1 Air-tight test vessel, for a sample of oil sufficient to immerse the membrane completely. NOTEA test vessel of volume500mL has been found satisfactory. 3.2 Dew-point hygrometer, to measure the dew-point down to
22、 40 C. NOTEA suitable instrument has an accuracy of about 0.5 C from ambient temperature down to20 C but the accuracy may fall at lower dew-points. A suitable hygrometer uses a light beam directed on to a cooled mirror and reflected on to a photo-transistor. Attenuation of the light beam by a deposi
23、t of dew on the mirror changes the current in the photo-transistor, and this change is amplified to control the mirror temperature at the dew-point temperature of the enclosed air. (SeeFigure 1.) 3.3 Semi-permeable tubular membrane, attached to a system of minimum volume for circulating air past the
24、 hygrometer. 3.4 Electromechanical diaphragm pump, to circulate air through the system at a rate of approximately0.5L/min. 3.5 Bypass drying chamber, containing desiccant. 3.6 Magnetic stirrer, with glass or polytetrafluoroethylene covered stirrer bar. 4 Sample preparation Sampling containers, test
25、vessels and all items coming into contact with the oil shall be cleaned and dried in accordance with BS5263. Sampling of the oil shall be in accordance with BS5263 and BS5574. Transfer the oil to the test vessel with minimum contact with air. NOTEMany potential errors introduced by the use of interm
26、ediate sampling containers may be avoided by sampling directly into the test vessel. 5 Procedure 5.1 Ensure that the desiccant in the drying chamber is dry. This may be checked by using the apparatus to circulate air through the drying chamber and past the mirror with the membrane in an empty test v
27、essel. If the desiccant is dry the dew-point will be lower than30 C. 5.2 Operate the circulating pump for5min to pass air through the system and desiccant with the membrane in the atmosphere; this will raise the mirror temperature a little and help avoid major upswing of temperature when the membran
28、e is immersed in oil, should this be particularly wet. 5.3 Change the bypass valve to isolate the drying chamber. Place the test vessel containing the oil sample into position, ensuring that the membrane is completely immersed and leaving no more than10% space above the oil. It is necessary that the
29、 test vessel sealing is air-tight. 5.4 Stir the oil at approximately300r/min for30min with the pump continuing to circulate air. Record the dew-point temperature and the oil temperature at25min and30min. If these readings differ by more than1 C check the apparatus for leaks and if necessary retest w
30、ith a second filling. NOTEIn the apparatus described the mirror temperature cannot exceed ambient temperature. A dew-point indication of approximately ambient temperature is likely to be incorrect. 5.5 Determine the saturation vapour pressure corresponding to the dew-point temperature from standard
31、tables 1) . Record the value. 5.6 Determine the saturation vapour pressure corresponding to the sample temperature from the standard tables 1) . Record the value. 1) Standard tables of the vapour pressure of water at various temperatures can be found in the following: CRC Handbook of Chemistry and P
32、hysics, published annually by the Chemical Rubber Company Inc., Boca Raton, Florida, USA; Handbook of Chemistry, edited by N.A.Lange, published by McGraw-Hill International Publications Co. Ltd., 34 Dover Street, London W1.BS6522:1984 2 BSI 11-1999 5.7 The test may be repeated with the sample at one
33、 (or preferably more) temperatures above ambient to enable the percentage saturation versus temperature curve to be drawn. From this the percentage saturation at the various temperatures found in operation may be seen. NOTETo aid extrapolation and interpolation, note that a plot of temperature on a
34、linear scale against percentage saturation on a logarithmic scale normally approximates to a straight line. 6 Calculation of results The percentage saturation of the sample under test with water at the temperature noted is obtained by the following formula. 7 Precision The accuracy of determination
35、of percentage saturation depends on the accuracy which the dew-point is determined and, if this accuracy is 0.5 C as specified, then percentage saturation will be obtained within about2% at about10% saturation and1% at the highest saturations within the range of the apparatus. where A is the saturat
36、ion vapour pressure corresponding to the dew-point temperature (see5.5); B is the saturation vapour pressure corresponding to the sample temperature (see5.6). A B -100 BS 6522:1984 BSI 11-1999 3 Figure 1 Arrangement of equipment for the measurement of dew-point4 blankBS6522:1984 BSI 11-1999 Publicat
37、ions referred to BS5263, Method for sampling liquid dielectrics. BS5574, Guide for the sampling of gases and of oil from oil-filled electrical equipment and for the analysis of free and dissolved gases. BS6522:1984 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the in
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