1、STD-BSI BS EN bLb21-ENGL 1778 I Lb2LibbS b84723 015 9 BRITISH STANDARD Dry, solid insulating materials - Resistance test to high-voltage, low-current arc discharges The European Standard EN 61621 : 1997 has the status of a British Standard ICs 29.035.01 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PE
2、RMITTED BY COPYRIGHI LAW BS EN 61621 : 1998 IEC 61621 : 1997 BS EN 61621 : 1998 AmdNo. Date National foreword Text affected This British Standard is the English language version of EN 61621 : 1997. It is identical with IEC 61621 : 1997. The K participation in its preparation was entrusted by Technic
3、al Committee GEI15, Ins- materials, to Subcommittee GEI15/5, Methods of test, which has the responsibiliy to: - aid enquirem to undemtand the te - present to the responsible internationavEuropean committee any enquiries on the interpretation, or proposals for change, and keep the UK interests inform
4、ed; - monitor related international and European developments and promulgate them in the UK. This British Standard, having been prepared under the direction of the Eectrotechnicai Sector Board, was published under the authority of the Standards Board and comes into effect on 15 February 1998 O BSI 1
5、998 A list of organizations represented on this subcommittee can be obtained on request to its secretary. From 1 January 1997, all IEC publications have the number 6o added to the old number. For instance, IEC 27-1 has been renumbered as IEC 60027-1. For a period of time during the change over from
6、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 include an annex which lists nonnative references to intedonal publications with their corresponding European publication
7、s. The British Standards which implement these international or European publications may be found in the MI Standards Catalogue under the section entitled International Standards Correspondence Index, or by using the %in failure is also considered to have occurred if the arc causes a material to bu
8、rn and the burning continues when the arc is interrupted. NOTE 1 - When the arc disappears into the material, the circuit current usually changes and a noticeable change in sound takes place. NOTE 2 - For some materials, the trend towards failure increases over a fairly long interval of time before
9、all parts of the arc between the electrodes have disappeared. Failure only occurs when the entire arc has disappeared. NOTE 3 - For some materials, a persistent scintillation may be observed close to the electrodes after the arc has disappeared. This scintillation shall not be considered as part of
10、the arc. NOTE 4 - Burning of the material accompanying the arc is only considered as failure if the burning continues between arc interruptions. Otherwise the test is continued until a conducting path is formed. NOTE 5 - The first disappearance of the entire arc is considered as failure even if the
11、material recovers for subsequent arcing. 3.2 arc resistance total time in seconds from the start of test until specimen failure 4 Apparatus 4.1 Test circuit The principal components of the electrical circuit for the apparatus are shown in figure 1. NOTE - In the secondary circuit wiring the stray ca
12、pacitance should be less than 40 pF. Large stray capacitance may disturb the arc shape and influence the test results. 4.1.1 Transformer, T, A transformer with a rated secondary potential (on open circuit) of 15 kV, and a rated secondary current (on short circuit) of 60 mA, line frequency (48 Hz to
13、62 Hz). 4.1.2 Variable autotransformer, TC Rated 1 kVA and suitable for the line voltage. NOTE - A constant primary voltage supply f2 % is recommended. Page 6 EN 61621 : 1997 4.1.3 Voltmeter, VL AC voltmeter with an accuracy of +0,5 %, capable of reading line voltage :lg %. 4.1.4 Milliammeter, A A t
14、rue r.m.s. a.c. milliammeter capable of reading 10 mA to 40 mA with an accuracy of 15 %. Since this milliammeter is used only when setting up or making changes in the circuit, it may be shorted out by a bypass switch when not in use. NOTE - Although provision has been made for the suppression of rad
15、io frequency components of current in the arc, it may be desirable to check for their presence when the apparatus is first constructed. This is best done by use of a suitable thermocouple type r.f. milliammeter temporarily inserted in series with the milliammeter. 4.1.5 Current control resistors, Ri
16、o, R, R, and R, Four resistors are required in series with the primary of T,. These resistors must be adjustable, to some extent, to permit exact settings of the currents during calibration. RIO is always in the circuit to provide a 10 mA current. 4.1.6 Suppressing resistor, R, Rated at 15 khl i 1.5
17、 khl and at least 24 W. This resistor, along with the inductors (see 4.1.7) is used to suppress parasitic high frequency in the arc circuit. 4.1.7 Air core inductors, X, 1,2 H to 1,5 H NOTE - A single coil of this inductance is not practical. A satisfactory inductor may be constructed by connecting
18、in series eight coils of 3 O00 to 5 O00 turns of wire wound on insulating non-metallic cores of about 12,7 mm diameter and 153 mm inside length. 4.1.8 Breaker, 8 Motor driven or electronically operated interrupter used to give the required cycles for the three lower steps of the test by opening and
19、closing the primary circuit according to the schedule in table 1. with an accuracy of 10,008 s. 4.1.9 Timer, TT A stop watch or electric interval timer accurate to fl s. 4.1.10 Contactor C, When the draft shield, enclosing the electrode assembly, is in lowered position, it actuates a normally open (
20、NO) microswitch which, in turn, operates contactor C, and connects the transformer Tv to the circuit, allowing application of HV to the electrodes. With the draft shield raised, the transformer is disconnected and the operator is protected. STD-BSI BS EN bLb21-ENGL 1998 - Lb2LibbS Ub84732 191 Page 7
21、 EN 61621 : 1997 4.2 Electrodes and electrode assembly 4.2.1 Electrodes The electrodes are made from 2,4 mm f 0,05 mm diameter tungsten rod which is free from cracks, pits or rough spots. The free electrode length shall be a minimum of 20 mm. It is recommended that the electrodes are mounted in a sh
22、ank which allows correct orientation of the electrode tip after sharpening. The electrode tip shall be ground and polished to produce an angle of 30“ i 1“ to the axis, to achieve a fiat elliptical face. As an example, figure 2 shows the electrodes mounted in a suitable shank. NOTE 1 - Tungsten weldi
23、ng rods have been found to be suitable for use as electrodes. NOTE 2 - A steel jig for securing the electrodes during sharpening io ensure finishing the pointed tips to the proper geometry is helpful. 4.2.2 Electrode assembly This assembly provides a means of holding the electrodes and the test spec
24、imen at the proper angle for applying the arc to the top surface of the test specimen. It shall be constructed so that the top surface of each specimen is at the same height for each test. Each electrode shall be adjusted so that it rests independently on the test specimen with a force of 0,5 N f 0,
25、05 N. The test specimen shall be protected from air drafts, and shall be allowed venting of combustion products in cases where test specimens give off smoke or gases during the test. The electrodes shall be positioned so that when they are resting on a test specimen, they lie in the same vertical pl
26、ane and are both inclined 35“ f lo from the horizontal (thus the angle between the axis of the electrodes is 110“ i 2“), as shown in figure 3. The minor axes of the elliptical tip surfaces shall be horizontal with the spacing of the tips adjusted to 6,35 rnm f Oll mm. A clear view shall be provided
27、of the arc from a position slightly above the plane of the specimen. NOTE - Air flow requirement is under consideration. 4.2.3 Cleaning and sharpening electrodes 4.2.3.1 Cleaning a) After every test the electrodes shall be cleaned with a solvent such as acetone or ethanol applied with a lint-free la
28、boratory tissue. Finish the cleaning of the electrodes by wetting them with deionized water and wiping dry with a clean, dry, lint-free tissue. b) If an excessive amount of combustion material remains on the electrodes after the above cleaning, then the application of a continuous 40 mA arc for appr
29、oximately 1 min (without a test specimen in place) has proven to be effective in above. 4.2.3.2 Sharpening The electrodes shall be maintained in the condition where they show an original elliptical face, and have no burrs or rough edges when viewed under 15x magnification. If the conditions describe
30、d above are not met, then the electrodes need to be sharpened. c STD-BSI BS EN bLb2L-ENGL 1778 Lb24bb7 Ob84732 028 Page 8 EN 61621 : 1997 4.3 Test chamber In order to avoid air drafts, the test chamber shall be an enclosure without venting and with dimensions not smaller than 300 mm x 150 mm x 100 m
31、m. 4.4 Calibration 4.4.1 Open circuit operating voltage The voltage shall be adjusted in the open circuit to 12,5 kV. It is measured by the voltmeter VL using the ratio of primary to secondary voltage of the open circuit. 4.4.2 Adjustment of secondary current With the correctly spaced electrodes res
32、ting on a ceramic block and with the draft shield closed, the equipment shall be energized and the current adjusted by means of the variable resistors RI, R, R, and 5 Specimens 5.1 from each material. For standard comparison of materials, at least five tests shall be made on specimens 5.2 The test s
33、pecimen thickness shall be 3 mm 3,; mm. Use of other thicknesses shall be reported. 5.3 Each test specimen shall have the necessary dimensions so that the test shall be performed on a flat surface and the electrode assembly shall not be closer than 6 mm to the edge of the test specimen nor closer th
34、an 12 mm to a previously tested area. Test thin materials by first clamping them tightly together to form a test specimen of a thickness as close to the recommended thickness as possible. 5.4 When moulded parts are tested the arc shall be applied to a location deemed most significant. Comparison tes
35、ts of parts shall be made in similar locations. 5.5 Dust, moisture, finger prints, etc. should be removed before testing, using a suitable method. Warning: The cleaning procedure may affect the material. 6 Conditioning The test specimens shall be exposed to a standard atmosphere of 23 OC f 2 OC, 50
36、% f 5 % relative humidity (standard atmosphere B in accordance with IEC 60212) for a minimum of 24 h, unless otherwise specified. 7 Procedure 7.1 For determination of the arc resistance the test specimen is placed in the electrode assembly and the spacing of the electrodes is adjusted to 6,35 mm f O
37、ll mm. * vi * STDeBSI BS EN blb2L-ENGL 1798 9 Zb24bb7 0b81i933 Tb4 W Page 9 EN 61621 : 1997 7.2 Activate the test circuit and observe the initiation of the arc, tracking progress and any peculiarities of the material under test. If the first test at any test step proceeds in a normal manner, then it
38、 is not necessary to closely watch the subsequent tests. Warning: During observation of the arc the operator should use anti-UV spectacles or an UV- shield. The initial arcs are observed in order to determine if they remain flat and adjacent to the test specimen surface. If the top of the arc approa
39、ches approximately 2 mrn above the surface of the test specimen or the arc climbs up the electrode instead of remaining on the tip or flares irregularly, it is an indication that the circuit constants are not correct or the material is releasing gaseous products at an excessive rate. 7.3 At the end
40、of each minute the arc severity in sequence as shown in table 1 is to be increased until failure occurs as defined in 3.2. Upon failure the arc current shall be immediately interrupted and the interval timer stopped. The time to failure in seconds is recorded for each of the five tests. 8 Results 8.
41、1 The result of this test is the time to failure, expressed in seconds. NOTE - Materials often fail within the first few seconds after a change in severity. When comparing the arc resistance of materials, much more weight should be given to a few seconds that overlap two stages than to the same elap
42、sed time within a single stage. Thus there is much greater difference in arc resistance between 178 s and 162 s than between 174 8 and 178 s. 8.2 Four general types of failure have been observed. 8.2.1 Many inorganic dielectrics become incandescent, whereupon they are capable of conducting the curre
43、nt. Upon cooling, however, they return to their earlier insulating condition. 8.2.2 Some organic compounds burst into flame without the formation of a visible conducting path in the substance. 8.2.3 Others are seen to fail by “tracking“, that is, a thin wiry line is formed between the electrodes as
44、the arc disappears. 8.2.4 The fourth type occurs by carbonization of the surface until sufficient carbon is present to carry the current. 9 Report The report shall include the following information: 9.1 identification of the test material and thickness tested; 9.2 details of any cleaning and conditi
45、oning prior to test; 9.3 central value, minimum and maximum arc resistance times; 9.4 special observations, for example, burning and softening. STD-BSI BS EN bLb2L-ENGL 1998 = Lb24bb7 Ob84934 9TO Page 10 EN 61621 : 1997 1 14 1 12 10 20 Table 1 - Sequence of 1 min steps - 10 114 on, 314 off 120 10 11
46、4 on, 114 off 180 10 Continuous 240 20 Continuous 300 I Current I Time cycle ) 1 Total time I mA S S Step I I 1 I8 I 10 I 118 on, 7/8 off I 60 I I 30 I 30 I Continuous I 360 I I _ 40 40 Continuous 420 I In the first three steps, an interrupted arc has been specified to make the test less severe than
47、 with a continuous arc. A current of 10 mA is specified because a lower current would tend to produce an unsteady or flaring arc. STD.BSI BS EN bLb21-ENGL 1778 Lb24bb7 Ob84935 837 Page 11 EN 61621 : 1997 / Pecimen / 1,2 H 1,5 H Timer l-r and breaker B I . I d P1 I I IEC 1222/97 Figure 1 - Example fo
48、r electrical circuit STD-BSI BS EN bLb2L-ENGL 1998 D Lb2LibbS Ob493b 773 Page 12 EN 61621 : 1997 O Shank Electrode Dimensions in millimetres IEC 122W97 Figure 2 - Electrode mounted in a shank (example) STD-BSI BS EN bLb21-ENGL 1998 D Lb24bb9 b84937 bOT 9 Page 13 EN 61621 : 1997 adjustment 5 Table Sp
49、ecimen/ * * u) IEC 12241(17 Dimensions in millimetres Figure 3 - Electrode assembly (example) STD-BSI BS EN bLbZL-ENGL 1998 W Lb24bbS Ob84938 54b W Page 14 EN 61621 : 1997 Annex ZA (normative) Normative references to international publications with their corresponding European publications This 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 publications are listed
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