1、BRITISH STANDARD BS 7713:1993 IEC 944:1988 Guide for the maintenance of silicone transformer liquidsBS 7713:1993 This British Standard, having been prepared under the directionof the Cables and Insulation Standards Policy Committee, was published underthe authority of the Standards Board and comes i
2、ntoeffect on 15November1993 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference CIL/10 Draft for comment 85/32912 DC ISBN 0 580 22582 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Cables
3、and Insulation Standards Policy Committee (CIL/-) to Technical Committee CIL/10 upon which the following bodies were represented: Association of Consulting Engineers Chemical Industries Association Electricity Industry in United Kingdom ERA Technology Ltd. Health and Safety Executive Institute of Pe
4、troleum Transmission and Distribution Association (BEAMA Ltd.) The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British (AC) Capacitor Manufacturers Association (BEAMA Ltd.) British Cable Makers Confederation British Lubricants Federation
5、Ltd. National Association of Waste Disposal Contractors Amendments issued since publication Amd. No. Date CommentsBS 7713:1993 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Tests and their significance 1 3 Frequency of examination of silicone
6、liquid in service 2 4 Sampling 2 5 Testing procedures 2 6 Classification of silicone transformer liquid in service 2 7 Treatment of silicone transformer liquid in Group2 3 8 Handling materials 3 List of references Inside back coverBS 7713:1993 ii BSI 10-1999 National foreword This British Standard h
7、as been prepared under the direction of the Cables and Insulation Standards Policy Committee. It is identical with IEC944:1988 Guide for the maintenance of silicone transformer liquids, published by the International Electrotechnical Commission (IEC). IEC944:1988 was prepared by IEC Technical Commit
8、tee No. 10, Fluids for electrotechnical applications. The United Kingdom participation in the drafting was provided by Technical Committee CIL/10, Fluids for electrotechnical applications. WARNING NOTE. This British Standard calls for the use of substances that may be injurious to health if adequate
9、 precautions are not taken. It refers only to technical suitability and does not absolve the user from legal obligations relating to health and safety at any stage. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible f
10、or their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-reference International Standard Corresponding British Standard IEC 836:1988 BS 7704:1993 Specifications for silicone liquids for electrical purposes (Implements CENELEC
11、HD565S1) (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendmen
12、t table on the inside front cover.BS 7713:1993 BSI 10-1999 1 1 Scope This standard is a guide to the maintenance of silicone liquids in transformers with rated voltages up to35kV and is intended to assist the equipment operator in assessing the quality of the liquid during use in the equipment and m
13、aintaining it in serviceable condition. Methods for reconditioning silicone transformer liquid are outlined. It deals only with silicone liquids used in equipment where liquid sampling is practicable and which has not previously been filled with any other liquid. 2 Tests and their significance There
14、 are several tests which can be applied to silicone transformer liquids to determine their suitability for further use or whether corrective action is necessary. The appropriate method of test is indicated by cross-reference to the relevant clause in IECPublication836, Section2 Test methods. 2.1 Col
15、our and appearance Cloudiness or visible solid particles indicate that the materials should be dried and/or filtered. A modification of the colour indicates contamination, and electrical tests should be carried out. 2.2 Density Changes in density normally indicate contamination by other liquids. 2.3
16、 Kinematic viscosity The viscosity of silicone transformer liquid rarely changes even after long periods of service. A value outside the normal values given in Section3 of IECPublication836 indicates contamination by other substances or possibly severe and prolonged overheating. 2.4 Flash-point Fire
17、-point Diminution of the flash-point or fire-point is normally due to contamination by other liquids. It may also occur as the result of severe degradation of the liquid, suggesting a fault in the transformer. In the latter case, other properties could also be affected. 2.5 Water content A value abo
18、ve that specified indicates undesirable operating conditions and the need for corrective action, such as circulating the liquid through a suitable drier and replacing drying tubes where fitted. 2.6 Breakdown voltage A reduced value may be due to the presence of water or to particulate contamination
19、of the liquid. Remedial treatment of the liquid should be considered. 2.7 D.C. resistivity A reduced value suggests contamination by water or soluble impurities. Remedial treatment of the liquid should be considered. 2.8 Dielectric dissipation factor An increased value may well indicate degradation
20、of the silicone liquid or contamination by water or other impurities. Remedial treatment of the liquid should be considered. Property Clause Colour and appearance 8 Density 9 Kinematic viscosity 10 Flash-point 11 Fire-point 12 Water content 16 Breakdown voltage 19 D.C. resistivity 20 Dielectric diss
21、ipation factor 20BS 7713:1993 2 BSI 10-1999 3 Frequency of examination of silicone liquid in service It is not possible to specify a frequency of examination which meets all service conditions. For air-breathing transformers, a simple visual inspection should be carried out at six-month intervals to
22、 ensure that drying devices are effective. When this condition is met, testing at five-year intervals is suggested. Completely sealed transformers should not require testing of the liquid more frequently than every five years. 4 Sampling Sampling should be carried out during or as soon as possible a
23、fter normal operation by the procedures described in Clause7 of IECPublication836. It is imperative that all precautions described be adhered to in order to avoid erroneous test results and retesting. Silicone transformer liquid has a relative density of less than unity at ambient and working temper
24、atures. Samples should be taken from the bottom of the equipment as this represents the least favourable condition. 5 Testing procedures 5.1 Field screening tests Field tests are usually limited to visual inspection and either volume resistivity and/or breakdown voltage. 5.2 Laboratory tests Laborat
25、ory tests may include most or all of the tests listed in Clause2 of this publication as these often enable the cause of degradation or the source of contamination to be recognized. 6 Classification of silicone transformer liquid in service Based on current industrial experience, silicone liquids in
26、service can be classified as follows: Group 1 This group consists of liquids that are in satisfactory condition for continued use. The following properties are considered to be satisfactory for35kV or lower voltage transformers: For compact high stress transformers (e.g.locomotives) higher limits ma
27、y be needed, for example: Group 2 This group consists of liquids which require treatment to restore them to usable condition: any liquid not meeting the above parameters. appearance clear, colourless breakdown voltage 30 kV d.c. resistivity at ambient temperature 1 10 117.m fire-point 300 C breakdow
28、n voltage 45 kV d.c. resistivity at ambient temperature 1 10 127.mBS 7713:1993 BSI 10-1999 3 7 Treatment of silicone transformer liquid in Group2 Reconditioning may be carried out by one of the two following methods, using equipment commensurate with the quantity of liquid to be processed. 7.1 Vacuu
29、m treatment and filtration The silicone, liquid, preferably heated to6080 C, should be sprayed into a vacuum chamber, or poured over baffle plates to give a large surface area of liquid. The pressure should be as low as possible;0.1kPa or less is attainable in practice. A filter of510 4m pore size s
30、hould be placed on the exit side of the unit. 7.2 Molecular sieve and filtration In this method the liquid is passed through a bed of thoroughly dried molecular sieve beads at ambient temperature, then passed through a filter of nominal5104m pore size. NOTEIf the material cannot be rendered usable a
31、fter reconditioning it should be disposed of as described in IECPublication836, Section1, Clause5. 8 Handling materials Precautions normally taken with dielectric liquids to prevent contamination from water, damp atmospheres and solid particles should be applied when handling silicone transformer li
32、quid. Steel, copper, aluminium, brass and bronze as well as a wide variety of conventional solid insulating materials may be used in contact with silicone transformer liquids. Unless shown to be suitable for the purpose, silicone elastomers should not be used with silicone liquids. Centrifugal pumps
33、 and gear pumps in which both gears are driven are recommended for use with silicone liquid. Pumps and other devices in which mild steel slides on mild steel cannot be used, although some hardened steels have been found to be satisfactory. WARNING NOTE: Small quantities of silicone liquid can cause
34、excessive foaming in mineral insulating oil. To avoid such contamination, the use of the same equipment to handle both silicone liquids and mineral oils should be avoided.4 blankBS 7713:1993 BSI 10-1999 List of references See national foreword.BS 7713:1993 IEC944:1988 BSI 389 Chiswick High Road Lond
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