1、BRITISH STANDARD BS EN 61868:1999 IEC61868: 1998 Mineral insulating oils Determination of kinematic viscosity at very low temperatures The European Standard EN61868:1999 has the status of a BritishStandard ICS29.040.10BSEN61868:1999 This BritishStandard, having been prepared under the directionof th
2、e ElectrotechnicalSector Committee, was published underthe authority of the Standards Committee and comesinto effect on 15 April1999 BSI02-2000 ISBN 0 580 32187 8 National foreword This BritishStandard is the English language version of EN61868:1999. It is identical with IEC61868:1998. The UK partic
3、ipation in its preparation was entrusted to Technical Committee GEL/10, Fluids for electrotechnical applications, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for c
4、hange, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. From1 January1997, all IEC publications have the number60000 added to t
5、he old number. For instance, IEC27-1 has been renumbered as IEC60027-1. For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems. Cross-references Attention is drawn to the fact that CEN and CENELEC Standards normally
6、include an annex which lists normative references to international publications with their corresponding European publications. The BritishStandards which implement these international or European may be found in the BSI Standards Catalogue under the section entitled “International Standards Corresp
7、ondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not
8、of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theEN title page, pages2 to7 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be ind
9、icated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBSEN61868:1999 BSI 02-2000 i Contents Page National foreword Inside front cover Foreword 2 Text of EN61868 3ii blankEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN61868 January1999
10、 ICS17.220.99; 29.035.40 Descriptors: Liquid electrical insulatingmaterials, mineral oils, insulating oils, viscosity measurements, kinematic viscosity, low temperature tests, computation English version Mineral insulating oils Determination of kinematic viscosity at very low temperatures (IEC61868:
11、1998) Huiles minrales isolantes Dtermination de la viscosit cinmatique trs basse temprature (CEI61868:1998) Isolierle auf Minerallbasis Bestimmung der kinematischen Viskositt bei sehr niedrigen Temperaturen (IEC61868:1998) This European Standard was approved by CENELEC on1999-01-01. CENELEC members
12、are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application t
13、o the Central Secretariat or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has t
14、he same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingdom. CENE
15、LEC European Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels 1999 CENELEC All rights of exploitation in any form and by any means reserved worldwid
16、e for CENELEC members. Ref. No. EN61868:1999 EEN61868:1999 BSI 02-2000 2 Foreword The text of document10/443/FDIS, future edition1 of IEC61868, prepared by IEC TC10, Fluids for electrotechnical applications, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN61868 on1999
17、-01-01. The following dates were fixed: Endorsement notice The text of the International Standard IEC61868:1998 was approved by CENELEC as a European Standard without any modification. Contents Page Foreword 2 Introduction 3 1 Scope 3 2 Normative references 3 3 Definitions 3 4 Principle 3 5 Apparatu
18、s 3 6 Calibration 4 7 Procedure 5 8 Expression of results 6 Figure 1 Viscometer bath and accessories 7 latest date by which the ENhas to be implemented at national level by publication of an identical national standard or by endorsement (dop) 1999-10-01 latest date by which the national standards co
19、nflicting with the EN haveto be withdrawn (dow) 2001-10-01EN61868:1999 BSI 02-2000 3 Introduction Non-Newtonian behaviour and significant increases in viscosity at very low temperatures have been observed in some mineral insulating oils as a result of microcrystalline growth, with a potential risk o
20、f failure for electrical equipment re-energized under very cold weather conditions. Microcrystalline formation is a slow process, which can take relatively long periods of low-temperature soaking to show its full effects, and which can also be destroyed by inducing movement in the oil, possibly as a
21、 result of heat producing friction or shear forces. This standard presents the adaptations to be made to ISO3104 to take into account these effects and to allow the measurement of kinematic viscosity at very low temperatures, without subjecting the oil sample to warming or undue movement during meas
22、urement, and with the application of a soaking period, in order to adequately simulate the flow of oil in electrical equipment, for example in the small cooling passages and timing mechanisms of transformers. 1 Scope This International Standard specifies a procedure for the determination of the kine
23、matic viscosity of mineral insulating oils, both transparent and opaque, at very low temperatures, after a cold soaking period of at least20h, by measuring the time for a volume of liquid to flow under gravity through a calibrated glass capillary viscometer. It is applicable at all temperatures to b
24、oth Newtonian and non-Newtonian liquids having viscosities of up to20000mm 2 s 1 . It is particularly suitable for the measurement of the kinematic viscosity of liquids for use in cold climates, at very low temperatures(40 C) or at temperatures between the cloud and pour-point temperatures(typically
25、20 C) where some liquids may develop unexpectedly high viscosities under cold soak conditions. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edit
26、ions indicated were valid. All normative documents are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and ISO maintain re
27、gisters of currently valid International Standards. ISO3104:1994, Petroleum products Transparent and opaque liquids Determination of kinematic viscosity and calculation of dynamic viscosity. ISO3105:1994, Glass capillary kinematic viscometers Specification and operating instructions. 3 Definitions F
28、or the purpose of this International Standard, the following definitions apply: 3.1 kinematic viscosity the ratio between the viscosity and the density of the liquid. It is a measure of the resistance to flow of a liquid under gravity NOTEIn the SI, the unit of kinematic viscosity is the square metr
29、e per second (m 2 s 1 ). 3.2 newtonian liquid a liquid having a viscosity that is independent of the shear stress or shear rate. If the ratio of shear stress to shear rate is not constant, the liquid is non-Newtonian 4 Principle The time is measured, in seconds, for a fixed volume of liquid to flow
30、under gravity through the capillary of a calibrated viscometer under a reproducible driving head and at a closely controlled temperature. The kinematic viscosity is the product of the measured flow time and the calibration constant of the viscometer derived by direct calibration with a certified ref
31、erence oil according to ISO3104. 5 Apparatus 5.1 Viscometers Viscometers of the glass capillary type, calibrated and capable of measuring kinematic viscosity within the limits of precision given in8.2, are acceptable(seenote1). The viscometers listed in ISO3105 meet these requirements(seenote2). Use
32、 only calibrated viscometers with constants measured and expressed to the nearest0,1% of their respective values. It is not intended to restrict this standard either to the use of only those viscometers or to the use of U tube viscometers; however, glass capillary viscometers of the Cannon Fenske Ro
33、utine type (series500 and600), with constants between8mm 2 s 2and20mm 2 s 2 , have been found particularly suitable at very low temperatures. NOTE 1Procedures for the calibration of viscometers are given in ISO Standard3105.EN61868:1999 4 BSI 02-2000 NOTE 2The calibration constant C is dependent upo
34、n the gravitational acceleration at the place of calibration and this shall, therefore, be supplied by the calibration laboratory together with the instrument constant. Where the acceleration of gravity g in the two locations differs by more than0,1%, correct the calibration constant as follows: whe
35、re the subscripts1 and2 indicate respectively the calibration laboratory and the testing laboratory. 5.2 Viscometer holders The holder shall allow the viscometer to be suspended in a position similar to that adopted for calibration. The proper alignment of a vertical datum part may be confirmed by u
36、sing a plumb line. 5.3 Viscometer bath and accessories A suitable set-up, placed in a freezer tank, is described in Figure 1. Any transparent liquid bath may be used provided that it is of sufficient depth that at no time during the measurement will any portion of the sample in the viscometer be les
37、s than20mm below the surface of the bath liquid or less than20mm above the bottom of the bath. Methanol has been found appropriate as a bath medium. However, any liquid which is clear, does not freeze at operating temperature, and does no harm to the silicone-based caulking material used for the gla
38、ss bath construction, can be used instead of methanol, for example2-propanol. The temperature control shall be such that the temperature of the bath medium does not vary by more than0,03 C over the length of the viscometers, or between the position of each viscometer, or at the location of the therm
39、ometer. 5.4 Temperature measuring device Calibrated liquid-in-glass thermometers of a minimum accuracy after correction of0,02 C may be used, or any other thermometric or battery-operated device of equal accuracy. All readings and corrections shall be made at least to the nearest0,02 C. IP Standard
40、thermometer68C or ASTM standard thermometer73C (corresponding to ASTM specification E1), containing a suitable mercury thallium alloy, have been found appropriate. These thermometers have0,05 C graduations, but allow interpolations to be made by good operators down to0,01 C. 5.5 Timing device Any ti
41、ming device may be used provided that the readings can be taken by the operator with a discrimination of0,2s or better, and that it has an accuracy of less than0,01% when tested over intervals of15min. Electrical timing devices may be used if the current frequency is continuously controlled to an ac
42、curacy of0,01% or better. Alternating currents, as provided by some public power systems, are intermittently rather than continuously controlled. When used to activate electrical timing devices, such control can cause large errors in viscosity flow measurements. Synchronous clocks, dependent on powe
43、r frequency, should meet this accuracy requirement, as should a high quality mechanical stopwatch, although a quartz-based stopwatch, checked against a broadcast time standard, or a synchronous clock that is driven by a large interconnected power system would be preferred. 6 Calibration 6.1 Viscomet
44、ers Use only calibrated viscometers with constants measured and expressed to the nearest0,1% of their respective values. 6.2 Thermometers Calibrated liquid-in-glass thermometers shall be checked to the nearest0,02 C by direct comparison with a suitable certified reference thermometer. 6.2.1 Calibrat
45、ed thermometers shall be checked for accuracy at total immersion, which means immersion to the top of the mercury-thallium alloy column, with the remainder of the stem and the expansion chamber at the top of the thermometer exposed to the freezers temperature; the expansion bulb should not be immers
46、ed in the liquid. 6.2.2 The ice point of calibrated thermometers shall be determined periodically and the certified correction shall be adjusted to conform to any change in the ice point. The possible change in the ice point reading of new thermometers may require checking every week. Checking at th
47、e ice point has been found most appropriate and sufficient. However, checking at the operating temperature against a traceable device may also be used, provided it has the required accuracy. 6.2.3 Thermocouples or other electrical temperature measuring devices may also be used, provided they have th
48、e required accuracy and are suitably calibrated. 6.3 Timers Standard time signals available in some countries may be used for checking the accuracy of timing devices. C 2 g 2 g 1 -C 1 =EN61868:1999 BSI 02-2000 5 6.4 Viscosity oil standards Viscosity oil certified standards, when available, or a suit
49、able reference oil may be used as confirmatory checks on the procedure in the laboratory. If the measured kinematic viscosity does not agree within 0,5% of the certified or reference value, each step in the procedure shall be rechecked, including thermometer and viscometer calibration, to locate the source of anomalous result. 7 Procedure 7.1 The specific details of operation vary for the different types of viscometers listed in ISO3104. In all cases, however, proceed in accordance with7.2 to7.4 inclusive. 7.2 Mainta
