1、BRITISH STANDARD BS 903C4: 1983 BS 2782-2: Methods220 and221:1983 Methods of testing vulcanized rubber Part C4: Determination of electric strength Methods of testing plastics Part 2: Electrical properties Method 220: Determination of electric strength: rapidly applied voltage method Method 221: Dete
2、rmination of electric strength: step-by-step method IMPORTANT NOTE. When using this method in order to test plastics, readers are reminded that the foreword, general introduction and instructions toBS2782-0:1982 contain important information on the testing of plastics. However, it should be noted th
3、at the conditioning requirementsgiven in clause8 of this Part replace those in Part0. UDC 678.01:537.226.7BS903-C4:1983 BS2782-2:Methods 220 and 221:1983 This British Standard, having been prepared under the directionof the Plastics StandardsCommittee and theRubber Standards Committee,was published
4、underthe authority of the BoardofBSI and comes intoeffecton 30September1983 BSI 03-2000 BS 903-C4 first published July1957 First revision jointly with BS2782:Methods220 and221 September1983 The following BSI references relate to the work on this standard: Committee referencePLC/RUC/9 Drafts for comm
5、ent76/52548 DC 76/52549DC ISBN 0 580 13317 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics Standards Committee (PLC/-) and the Rubber Standards Committee (RUC/-) to Technical Committee PLC/RUC/9 upon which the following bodies
6、 were represented: British Plastics Federation British Rubber Manufacturers Association Electrical and Electronic and Insulation Association (BEAMA) Ministry of Defence Rubber and Plastics Research Association of Great Britain Telecommunication Engineering and Manufacturing Association (TEMA) Amendm
7、ents issued since publication Amd. No. Date of issue CommentsBS903-C4:1983 BS2782-2:Methods 220 and 221:1983 BSI 03-2000 i Contents Page Committees responsible Inside front cover Foreword ii 0 Introduction 1 1 Scope 1 2 Definitions 1 3 Identification of method 1 4 Form of test pieces 1 5 Number of t
8、est pieces 2 6 Electrodes and test assemblies 2 7 Electrical apparatus 4 8 Conditioning 4 9 Conditions of test 4 10 Procedure 5 11 Expression of results 5 12 Test report 6 Appendix A Criterion of breakdown 7 Figure 1 Electrodes for sheet materials 7 Figure 2 Typical example of electrode apparatus fo
9、r tests on tape 7 Figure 3 Electrodes for tests on round tubes 8 Figure 4 Typical electrode arrangement for tests parallel to the surface 8 Figure 5 Typical electrodes for tests on flexible tube including sleeving 9 Table 1 Identification of method 2 Table 2 Successive voltages to be applied (kilovo
10、lts peak/2) 5 Publications referred to Inside back coverBS903-C4:1983 BS2782-2:Methods 220 and 221:1983 ii BSI 03-2000 Foreword This revision of this Part of this British Standard which has been published under the direction of the Plastics Standards Committee and the Rubber Standards Committee supe
11、rsedes the previous edition of BS903-C4 and methods201A to201G of BS2782, which are being withdrawn. The standard includes information from IEC243:1967. In BS2782:1970 only the step-by-step methods were described. In preparing this standard to cover the testing of both vulcanized rubber and plastics
12、, there was some difficulty in reconciling the requirements for the period of conditioning the test pieces prior to testing. The internationally agreed period for vulcanized rubber is a minimum of16h (seeBS903-A35) but for plastics a minimum of88h is used (seeISO291). However, for most rubber and pl
13、astics, it is considered that16h is adequate in the climatic conditions prevailing in theUK. 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 no
14、t of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1to10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will
15、be indicated in the amendment table on the inside front cover.BS903-C4:1983 BS2782-2:Methods 220 and 221:1983 BSI 03-2000 1 0 Introduction The electric strength measured in accordance with this standard is not the intrinsic electric strength,i.e. the electric stress at which the material will fail u
16、nder ideal conditions, but a value which may be considerably less than this and which is usually controlled by such factors as the presence of discharges in the ambient gas or liquid or in gaseous inclusions in the material. It is meaningless to quote the electric strength of a material without comp
17、lete details of the test conditions, because the electric strength may be affected by many factors including: a) the frequency, waveform and time of application of the voltage; b) the thickness and homogeneity of the test piece and the presence of mechanical strain; c) the ambient temperature, press
18、ure and humidity; d) the presence of gaseous inclusions, moisture or other contamination; e) the dimensions and thermal conductivity of the test electrodes; f) the electrical and thermal characteristics of the ambient medium. The results given by different methods are not directly comparable and it
19、should be noted that the electric strength of many materials decreases as the thickness of the test piece between the electrodes increases and with increasing time of voltage application. Material with a high electric strength measured by the tests described in this standard will not necessarily res
20、ist long-term degradation processes such as erosion or chemical deterioration by discharges, or electrochemical deterioration in the presence of moisture, which may cause eventual failure in service at much lower stresses. On the other hand, if discharges in insulation are eliminated by appropriate
21、design and construction, the values obtained by the tests described in the standard may be exceeded. Thus, these tests are only of limited value to the insulation designer for comparative purposes although they are useful for routine and quality control tests, and as specification tests. 1 Scope Thi
22、s Part of this British Standard gives two methods of determining the short-time electric strength (breakdown voltage) of insulating vulcanized rubber (including ebonite) and of solid plastics materials using a voltage with a nominal frequency of50Hz. One method of determining electric strength is by
23、 rapidly increasing the voltage until breakdown occurs and the other is by a steady increase in the applied voltage step-by-step at20s intervals. Test pieces and electrode systems are specified to provide tests on a variety of materials and forms of material. Tests are carried out normal and paralle
24、l to the planes of sheet materials and tubes and parallel to the axes of rods. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard, the following definitions apply. 2.1 voltage the peak value of
25、the alternating voltage applied to the electrodes divided by2 2.2 breakdown voltage the voltage at which breakdown occurs in the rapidly applied voltage test or the highest voltage withstood for20s in the step-by-step method 2.3 electric strength the breakdown voltage divided by the dimension of the
26、 test piece across which the voltage was applied 2.4 central value the middle value of an odd number of results, or the mean of the middle two when arranged in order of magnitude 3 Identification of method Methods are identified according to the mode of applying the voltage and the nature of the mat
27、erial under test as indicated inTable 1. 4 Form of test pieces 4.1 General. If applicable the test piece shall be prepared under the conditions specified in the relevant British Standard for the material. The dimensions shall be as specified in4.2 to4.8; increases in the stated minimum dimensions ma
28、y be necessary to avoid breakdown through the surrounding medium,i.e. flashover. 4.2 Test pieces for MethodsC4.1A,C4.2A,220A and221A. The test piece shall be a disc not less than100mm in diameter or a square of side not less than100mm. Where the material is supplied in sheet form the thickness shall
29、 be the thickness of the sheet.BS903-C4:1983 BS2782-2:Methods 220 and 221:1983 2 BSI 03-2000 For rigid moulded or cast materials the average thickness of the test piece shall be3 0.2mm. In addition, on any one test piece the thickness shall not vary by more than0.2mm. For flexible moulded or cast ma
30、terials the average thickness of the test piece shall be1.25 0.2mm. Inaddition, on any one test piece the thickness shall not vary by more than0.1mm. 4.3 Test pieces for MethodsC4.1B,C4.2B,220B and221B. The test piece shall be a narrow strip or tape, at least250mm long, the width and thickness of th
31、e material except when the width needs to be reduced to fit any jig such as that shown inFigure 2. NOTEFor narrow tapes flashover may present difficulties, Flashover may be unavoidable with narrow tapes of some materials so that the maximum width should always be used. 4.4 Test pieces for Methods C4
32、.1C,C4.2C,220C and221C. The test piece shall be a rigid tube not less than100mm long. The wall thickness of the test piece shall be that of the tube from which it is cut. 4.5 Test pieces for MethodsC4.1D,C4.2D,220D and221D. The test piece shall be a flexible tube not less than100mm in length. The wa
33、ll thickness of the test piece shall be that of the tube from which it is cut. 4.6 Test pieces for MethodsC4.1E,C4.2E,220E and221E. The test piece shall be flexible tubing not less than350mm in length. The wall thickness of the test piece shall be that of the tube from which it is cut. 4.7 Test piec
34、es for MethodsC4.1F,C4.2F,220F and 221F. The test piece shall be flexible tubing not less than100mm in length. The wall thickness of the test piece shall be that of the tube from which it is cut. 4.8 Test pieces for MethodsC4.1G,C4.2G,220G and221G. The test piece ends shall be parallel smooth planes
35、 perpendicular to the plane of the sheet or axis of the rod or tube and25 0.2mm apart. The test piece shall be cut from the material without reduction in thickness. For sheet material the test piece shall be approximately100mm long. For rods and tubes up to100mm outer diameter or external side dimen
36、sion, the test piece shall be a complete ring or length of rod. For tubes over100mm outer diameter or external side dimension, the test piece shall be a portion of a ring approximately100mm circumferential length. 5 Number of test pieces The number of test pieces for the step-by-step method shall be
37、 two or as required by the specification for the material. Additional test pieces may be required if some tests are invalid (see10.3). The number of test pieces required for the rapidly applied voltage method shall be at least two or as required by the specification for the material, except in refer
38、ence cases when at least five test pieces shall be tested. In both cases additional test pieces may be required for preliminary tests. 6 Electrodes and test assemblies 6.1 General. The electrodes shall be kept clean and free from pitting including pitting caused by arcing. Table 1 Identification of
39、method Material under test Mode of applying voltage Direction of applying voltage BS903 reference BS2782 reference Sheet C4.1A 220A Narrow strip and tape C4.1B 220B Rigid tube Rapidly applied Normal to plane of the sheet or axis of tube C4.1C 220C Flexible tube including sleeving C4.1D, E and F 220D
40、, E andF Rigid sheet, tube and rod Parallel to the plane of the sheet or axis of tube or rod C4.1G 220G Sheet C4.2A 221A Narrow strip and tape C4.2B 221B Flexible tube including sleeving Step-by-step Normal to plane of the sheet or axis of tube C4.2C 221C C4.2D, E andF 221 D, EandF Rigid sheet, tube
41、 and rod Parallel to the plane of the sheet or axis of tube or rod C4.2G 221G BS903-C4:1983 BS2782-2:Methods 220 and 221:1983 BSI 03-2000 3 The lead to the upper electrode shall not tilt or otherwise move this electrode or affect the pressure on the test piece and the leads to the electrodes shall n
42、ot appreciably affect the electric field configuration in the neighbourhood of the test piece. 6.2 Electrodes for MethodsC4.1A,C4.2A,220A and221A. For sheet materials the lower electrode shall consist of a solid cylinder of brass or stainless steel75 1mm in diameter and approximately15mm thick. The
43、upper electrode shall consist of a solid cylinder of brass or stainless steel25 1mm in diameter and approximately25mm thick. The sharp edges shall be removed from the electrodes, the radius at the edges being approximately3mm. (SeeFigure 1.) 6.3 Electrodes for MethodsC4.1B,C4.2B,220B and221B. For na
44、rrow strips and tapes the electrodes shall be two brass or stainless steel rods, each6 0.2mm in diameter mounted vertically one above the other in a jig so that the test piece is held between the ends of the rods. The upper and lower electrodes shall be coaxial. The sharp edges of the ends shall be
45、removed to give a radius of approximately1mm. The upper electrode shall weigh50 2g. Figure 2 shows a convenient arrangement. NOTE 1To prevent flashover around the edges of narrow tapes the test piece may be clamped using strips of tape overlapping the edges of the test piece. Alternatively, gaskets
46、surrounding the electrodes may be used provided there is an annular space between electrode and gasket of about1.5mm. If test pieces are to be tested while extended they shall be clamped in a frame holding them in the required position relative to the assembly shown inFigure 2. NOTE 2Wrapping one en
47、d of the test piece round a rotatable rod is one convenient way of achieving the required extension. 6.4 Electrodes for MethodsC4.1C,C4.2C,220C and221C. For rigid round tubes and rigid rectangular tubes, having an internal diameter or minor dimension not exceeding100mm, the outer electrode shall be
48、a band of metal foil25 1mm wide wrapped tightly around the tube. The inner electrode shall be a closely fitting internal conductor,e.g. rod, tube, metal foil, making good contact with the inner surface. In each case, the ends of the inner electrode shall extend for at least25mm beyond the ends of th
49、e outer electrode. SeeFigure 3(a). For round tubes, having an internal diameter exceeding100mm, the internal electrode shall consist of a disc of metal foil251mm in diameter, sufficiently flexible to conform to the curvature of the inner surface of the tube. The external electrode shall consist of a band of metal foil75 1mm wide wrapped tightly round the outside of the tube symmetrically with respect to the internal electrode. SeeFigure 3(b). 6.5 Electrode
