1、- CENELEC *EN*bOL5b 95 = 3404583 OL7l105b 872 BRITISH STANDARD Insulating liquids - Determination of the breakdown voltage at power frequency - Test method The European Standard EN 60156 : 1995 has the status of a British Standard ICs 29.040.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED B
2、Y COPYRIGHT LAW 3s EN i0156 : 1996 EC 156 : 1995 BS EN 60166 : 1996 CENELEC +ENtbOL5b 95 34045133 OL7L057 709 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technicd Committee GW10, Flui the instrument then used shall be calibrated against
3、a standard up to the full voltage which it is desired to measure. A method of calibration which has been found satisfactory is the use of a transfer standard. This is an auxiliary measuring device which is connected in place of the test cell between the high-voltage terminals to which it presents th
4、e same impedance as the filled test cell. The auxiliary device is separately calibrated against a primary standard, for example, a sphere gap in accordance with IEC 52 (see also IEC 60). 4 Test assembly 4.1 Test cell The volume of the cell shall be between 350 ml and 600 ml. The cell shall be made o
5、f material that is electrically insulating, transparent and chemically inert, resistant to the insulating liquid and the cleaning agents which may be used. The cell shall be provided with a cover and shall be designed to permit easy removal of the electrodes for cleaning and maintenance. Examples of
6、 suitable cell designs are given in figures 1 and 2. 4.2 Electrodes The electrodes shall be made either of brass, bronze or austenitic stainless steel. They shall be polished and, in shape, either spherical (123 mm to 13,O mm diameter) as shown in figure 1 or partially spherical of the shape and dim
7、ensions given in figure 2. The axis of the electrode system shall be horizontal, and at least 40 mm below the surface of the test liquid in the cell. No part of the electrode shall be closer than 12 mm to the cell wall or stirrer. The gap between the electrodes shall be 250 mm * 0,05 mm. CENELEC *EN
8、*h015b 75 W 3404583 OL7LObb 711 = Page 7 EN 60156 : 1995 The electrodes shall be examined frequently for pitting or other damage, and shall be maintained or replaced as soon as such damage is observed. 4.3 Stirring (optional) The test may be conducted with or without stirring. Differences between te
9、sts with or without stirring have not been found statistically significant. A stirrer, however, may be convenient especially with apparatus capable of automatic operation. Stirring may be achieved by means of a two-bladed impeller of effective diameter 20 mm to 25 mm, axial depth 5 mm to 10 mm, rota
10、ting at a speed of 250 r.p.m to 300 r.p.m. The impeller shall not entrain air bubbles and preferably rotate in such a direction that the resulting liquid flow is directed downward. It shall be constructed so that it is easily cleaned. Stirring by means of a magnetic bar (20 mm to 25 mm in length and
11、 5 mm to 10 mm in diameter) is an acceptable alternative when there is no risk of removing magnetic particles. The dimensions of the stirring device shall conform to the ctearance requirements in 4.2. 5 Preparation of electrodes New electrodes, pitted electrodes, electrodes which have not been prope
12、rly stored for a considerable time shall be cleaned by the following procedure: - clean all surfaces with a suitable volatile solvent and allow the solvent to evaporate; - polish with fine abrasive powder (for example, jewellers rouge) or abrasive paper or cloth (for example, crocus cloth); - after
13、polishing, clean with petroleum spirit (reagent quality: boiling range 60 OC - 80 OC) followed by acetone (reagent quality); - assemble the electrodes in the cell, fill with a clean, unused insulating liquid of the type to be tested next, and raise the electrode voltage to breakdown 24 times. 6 Test
14、 assembly preparation It is recommended that a separate test cell assembly be reserved for each insulating liquid tY Pe- Test assemblies shall be stored in a dry place, covered and filled with dry insulating liquid of the type in regular use in the cell. On change of the type of liquid under test, r
15、emove all residues of the previous liquid with an appropriate solvent, rinse the assembly with clean, dry liquid of the same type as that to be tested, drain and refill. CENELEC *EN*bO156 95 = 3404583 0173067 658 Page 8 EN 60156 : 1995 7 Sampling 7.1 Sample containers Sample size should be approxima
16、tely three times the capacity of the test cell. Appropriate sample containers shall comply with IEC 475. An amber glass bottle is the preferred container. Clear glass bottles may be used but they shall be shielded from direct light until ready to be tested. Plastic containers which are not attacked
17、by the liquid to be tested may be used, but these shall not be used more than once. For sealing, screw caps with polyolefine or polytetrafluoroethylene insert are preferred. . Containers and caps shall be cleaned by washing with a suitable solvent to remove residues of an earlier sample. Containers
18、shall next be rinsed with acetone, traces of which shall be removed by blowing with warm air. After cleaning, containers shall be immediately capped and kept sealed until used. 7.2 Sampling technique Sampling of new and used insulating liquids shall be carried out in full compliance with procedures
19、detailed in IEC 475. When sampling, containers should be almost filled with sample, leaving about 3 70 of the container volume as free air space. Breakdown voltage is extremely sensitive to the slightest contamination of the sample by water and particulate matters. Special reference is made to preca
20、utions necessary to avoid contamination of the sample and the need for trained personnel and experienced supervision. Unless otherwise required, the sample is taken where the liquid is likely to be most contaminated, usually at the lowest point of the container holding it. 8 Condition of the sample
21、The test is carried out, unless otherwise specified, on the sample as received without drying or degassing. At the time of test, the temperatures of the test liquid and ambient air shall not differ by more than 5 OC and for referee tests the liquid temperature shall be 20 OC f 5 OC. 9 Test procedure
22、 9.1 Sample preparation Immediately before filling the test cell, the sample container is gently agitated and turned over several times in such a way as to ensure as far as possible a homogeneous distribution of the impurities contained in the liquid without causing the formation of air bubbles. Unn
23、ecessary exposure to the ambient air of the sample shall be avoided. Page 9 EN 60156 : 1995 CENELEC *EN*b015b 95 3YOY583 0171Ob8 594 H 9.2 Filling of the cell Immediately before commencing the test, drain the test cell and rinse the walls, electrodes and other component parts, with the test sample.
24、Drain and slowly fill with the test sample avoiding the formation of air bubbles. Measure and record the temperature of the liquid. Position the cell in the test equipment and start the stirrer if used. 9.3 Application of voltage The first application of voltage is started approximately 5 min after
25、completion of filling and checking that no air bubbles are visible in the electrode gap. Apply voltage to the electrodes and uniformly increase voltage from zero at the rate of 2,O kV s-l * 0,2 kV s-l until breakdown occurs. The breakdown voltage is the maximum voltage reached at the time the circui
26、t is opened either automatically (established arc) or manually (visible or audible discharge detected). Record the value. Carry out six breakdowns on the same cell filling allowing a pause of at least 2 min after each breakdown before re-application of voltage. Check that no gas bubbles are present
27、within the electrode gap. If a stirrer is used, it shall run continuously throughout the test. Calculate the mean value of the six breakdowns in kilovolts. 10 Report Report the mean value, in kilovolts, of the six breakdowns as the test result. The report shall also include: the sample identificatio
28、n, the value of each individual breakdown, the type of electrodes used, the frequency of the test voltage, the temperature of the liquid, the use of a stirrer (if any). 11 Test data dispersion The scatter of individual breakdown voltages has been found to be very dependent on the value of the result
29、. The graphical representation of figure 3 indicates the values of standard deviation/mean ratio which have been found in a large body of test data in several laboratories using transformer oil. The full line in the graph shows the distribution of the median value of SD/mean as a function of the val
30、ue of the mean. The dotted lines indicate the expected 95 % range of values of SD/mean as a function of the value of the mean. CENELEC *EN*bOLSb 95 = 3404583 OL7LOb 420 Page 10 EN 60156 : 1995 110 - Rsine poxyde Epoxy resin 100 II I . -112- Figure 1 - Exemple dune cellule et dlectrodes sphriques app
31、ropries Example of suitable cell and spherical electrodes Mthacrylate de mthyle Methyl methacrylate Figure 2 - Exemple dune cellule et dlectrodes hmisphriques appropries Example of suitable cell and partially spherical electrodes Page 11 EN 60156 : 1995 Figure 3 - Reprsentation graphique du coeffici
32、ent de variation (rapport de lcart type a ia valeur moyenne) en fonction de la moyenne de tension de claquage Graphical representation of coefficient of variation (standard deviation/ mean ratio) versus mean breakdown voltage CENELEC *EN*b02Sb 95 3404583 0171071 089 Page 12 EN 60156 : 1995 Annex ZA
33、(normative) Normative references to international publications with their corresponding European publications Thjs European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publ
34、ications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including a
35、mendments). NOTE. When an international publication has been modified by CENELEC Common modifications, indicated by (mod), the relevant EN/HD applies. Publication Year Title E“D Year IEC 52 1960 Recommendations for voltage memurernent by - - IEC 60 series High-voltage test techniques m 588.1 s1 1991
36、 IEC 475 1974 Method of sampling liquid dielectrics - mans of sphere-gaps (one sphere earthed) EN 60060-2 1994 - O BSI 1996 CENELEC +ENxbOLSb 95 rn 3404583 0373072 T35 rn BS EN 60156 : 1995 List of references See national foreword. CENELEC tENtb015b 95 m 3YOY583 0171073 951 m BS EN 60156 : 1996 IEC
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