1、BRITISH STANDARD BS 7816-3: 1998 IEC 61244-3: 1998 Long-term radiation ageing in polymers Part 3: Procedures for in-service monitoring of low-voltage cable materials ICS 29.035.20BS7816-3:1998 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board, was pu
2、blished underthe authority of the Standards Board and comes into effect on 15 July 1998 BSI 05-1999 ISBN 0 580 30035 8 National foreword This Part of BS 7816 reproduces verbatim IEC 61244-3:1998 and implements it as the UK national standard. NOTEIEC 61244-3:1998 is a Technical Report type 2, issued
3、as a “prospective standard for provisional application”. It is not to be regarded as an “International Standard”. A review will be carried out not later than three years after its publication, with the options of its extension for a further three years, or conversion to an International Standard, or
4、 withdrawal. The UK participation in its preparation was entrusted by Technical Committee GEL/15, Insulating materials, to Subcommittee GEL/15/5, Methods of test, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any en
5、quiries on the interpretation, or proposals for change, 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 subcommittee can be obtained on request to its secretary. From 1 January 1997
6、, all IEC publications have the number 60000 added to the 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 The British Stan
7、dards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standa
8、rd 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 of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, a
9、n inside front cover, pages i and ii, theCEI IEC title page, pages ii to iv, pages 1 to 30 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since
10、publication Amd. No. Date CommentsBS7816-3:1998 BSI 05-1999 i Contents Page National foreword Inside front cover Text of CEI IEC 61244-3 1ii blankBS7816-3:1998 ii BSI 05-1999 Contents Page Introduction 1 1 Scope 1 2 Requirements of a monitoring technique 1 3 Techniques available 1 3.1 Local tests wi
11、thout sampling 2 3.1.1 Indenter 2 3.1.2 Sonic velocity 3 3.1.3 Near infrared reflectance 3 3.1.4 Torque tester 4 3.2 Local tests with microsampling 4 3.2.1 Infrared spectroscopy (IR) 4 3.2.2 Oxidation induction time (OIT) 5 3.2.3 Plasticizer content 5 3.2.4 Density 6 3.3 Global tests with spatial re
12、solution 6 3.3.1 Time domain reflectometry (TDR) 6 3.3.2 Partial discharge (PD) 7 3.4 Global tests without spatial resolution 7 3.4.1 Time domain spectrometry (TDS) 7 3.4.2 Dielectric loss 7 3.4.3 Pass/fail tests 8 3.5 Paced tests 8 4 Summary 9 Annex A (informative) Bibliography 29 Figure 1 Cross-se
13、ction of the indenter 1 11 Figure 2 Effect of jacket temperature on indenter modulus of EPR/CSPE after thermal ageing 4 12 Figure 3 Results with indenter on EPR/CSPE cable 13 Figure 4 Results with indenter on kerite KR cable 14 Figure 5 Schematic diagram showing the operating principles of the sonic
14、 velocity meter 6 15 Figure 6 Sonic velocity test results 16 Figure 7 Variation in IR absorbance with wavelength for PVC material and the use of first derivative to eliminate baseline shifts 6 17 Figure 8 Correlation of first derivative of IR absorbance at 1640nm to 1650nm and elongation at break fo
15、r thermal ageing of PVC at110C 6 18 Figure 9 Schematic diagram of prototype device for torque measurement of cables 8 18 Figure 10 Elongation at break versus torque value for flame-retardant PVC cables thermally aged at158C 8 19 Figure 11 Elongation at break versus torque value for PVC cables expose
16、d to sequential radiation ageing to0,5MGy and thermal ageing at120C 8 19 Figure 12 Elongation at break versus torque value for PVC cables thermally aged at120C 8 20 Figure 13 Carbonyl absorbance as a function of the radiation dose for XLPE 11 20 Figure 14 Carbonyl absorbance as a function of thermal
17、 ageing for XLPE 10 21BS7816-3:1998 BSI 05-1999 iii Page Figure 15 Correlation between elongation at break and oxidation induction time for unfilled XLPE insulation thermally aged at130C 9 21 Figure 16 Correlation between elongation at break and oxidation induction time for EPR insulation thermally
18、aged at140C 9 22 Figure 17 Correlation between elongation at break and plasticizer content for PVC insulation thermally aged at120C 9 22 Figure 18 Correlation between elongation at break and density for radiation-aged cable insulation 15 23 Figure 19 Correlation between elongation at break and densi
19、ty for radiation-aged cable jackets 15 23 Figure 20 Density profiles through the thickness of unaged and radiation-aged XLPE 15 24 Figure 21 Time domain signature files for a lighting circuit with switches on and off, showing location of first switch 24 Figure 22 Schematic representation of a partia
20、l discharge signal propagating in a shielded cable and the signals recorded by the detection instrument 19 25 Figure 23 Spatial distribution of discharge pulses along a cable length (unshielded) containing a known defect at6,1m 20 25 Figure 24 Schematic diagram of the measuring set-up for time domai
21、n spectrometry 19 26 Figure 25 Time domain spectrometry measurements on thermally aged EPDM/CSPE cables 19 26 Figure 26 Effect of cable temperature on a tan versus frequency spectrum of an EVA cable 23 27 Figure 27 Effect of radiation dose rate on the tan versus frequency spectrum of XLPE insulation
22、 23 27 Figure 28 Effect of radiation ageing on the tan versus frequency spectrum of a PVC insulated cable 23 28 Figure 29 Correlation between tan at specific frequencies and elongation at break for PVC cables 23 28 Table 1 Summary of currently available techniques for cable condition monitoring 10 T
23、able 2 Current status of the most developed monitoring techniques 11iv blankBS7816-3:1998 BSI 05-1999 1 Introduction Polymers are widely used as electrical insulating materials (e.g. in cables for control, instrumentation and power) in environments in which they are exposed to radiation. In such app
24、lications, these materials may well be required to survive the full working life of the plant, which may be more than40 years, and accident conditions at the end of working life. Although considerable data are available on the behaviour of polymeric insulating materials under irradiation, there is s
25、till some uncertainty on the effects of long-term low dose rate irradiation, such as would be experienced by cables. There is therefore a requirement for techniques for monitoring the state of degradation of cable materials in situ throughout the lifetime of the plant. Suitable cable monitoring tech
26、niques would also be important to surveillance programmes in support of plant life extension and licence renewal. Although this report is primarily aimed at cable condition monitoring in nuclear power plants, it can also be applied to other polymeric components. Many of the techniques are equally ap
27、plicable to thermal-only ageing of polymeric components in conventional power plants. 1 Scope This technical report summarizes the main cable monitoring techniques which are currently being assessed worldwide. These techniques are primarily aimed at monitoring degradation of low-voltage cables. Most
28、 of the methods are at the development stage and require in-plant evaluation before they could be recommended as standard techniques. The advantages and disadvantages of each method, and its current state of development, are outlined in the following sections. There are two aspects of cable monitori
29、ng that need to be taken into account techniques suitable for ageing evaluation and techniques suitable for monitoring faults in cables. The methods discussed may, in some cases, be more suitable for monitoring faults than for evaluating the degree of degradation of the cable materials. 2 Requiremen
30、ts of a monitoring technique There is a range of requirements which the ideal cable monitoring technique would need to satisfy. In practice, no one technique will satisfy all of the requirements and a range of techniques is likely to be needed. In each case, baseline data (i.e. data on unaged materi
31、al of the same formulation and manufacturer) are needed to make full use of the techniques. The ideal monitoring technique would have the following attributes: non-destructive; capable of use during normal operation; not require disconnection of equipment; related to an identifiable degradation crit
32、erion; applicable to a wide range of cable materials and configuration; applicable at accessible locations; capable of identifying hot-spots; reproducible and capable of compensating for environmental conditions (temperature, humidity); less expensive to implement than periodic cable replacement; re
33、adily available reference data. 3 Techniques available There is a wide range of possible techniques being considered for cable monitoring. A few are already in use in-plant, others are only at the laboratory evaluation stage. The methods can be grouped together under generic types, as follows. Local
34、 tests without sampling indenter sonic velocity near infrared reflectance torque testing Local tests with micro-sampling infrared oxidation induction time (OIT) plasticizer content density Global tests with spatial resolution time domain reflectometry (TDR) partial discharge Global tests without spa
35、tial resolution dielectric loss time domain spectrometry (TDS) pass/fail tests dielectric strength, insulation resistance Paced tests elongation at break Each of these types of test is described in more detail in the following subclauses.BS7816-3:1998 2 BSI05-1999 3.1 Local tests without sampling Th
36、e term “local” refers to techniques which give information on the state of the cable at the measuring point only and are thus likely to miss defective spots. These methods can only be applied in man-accessible areas and are generally limited to tests of the cable jacket material except at terminatio
37、ns where the insulation is exposed. Where the techniques have been cross-correlated with changes in elongation at break, these methods have a predictive capability. This type of test will provide immediate data in-plant on the state of the cable. Where the cable jacket is more likely to degrade than
38、 the insulation (which is often true) the methods provide early warning of cable failure. Local bend tests by manipulation of the cable by hand can give qualitative information when carried out by experienced personnel. 3.1.1 Indenter The indenter is a portable device developed by the Franklin Insti
39、tute which measures a property related to the modulus of elasticity of cable jacket and insulation materials 1 2 1) . A schematic diagram of the indenter is shown in Figure 1. An instrumented probe of known shape is driven against the outside of the cable at a fixed velocity(12,7mm/min) and the slop
40、e of the force versus distance is obtained over a force range of2N to9N. The probe shape used is the same as that used in the ASTM standard for hardness testing 3, i.e. a truncated cone, but with an end area equal to half that of the ASTM cone. The indenter modulus values measured with the portable
41、indenter have to be corrected for temperature to obtain comparable data sets when used in-plant. The amount of temperature compensation required varies with the ageing of the cable material 4, see Figure 2. Practical tests of the unit in nuclear power plants have shown that the indenter can be succe
42、ssfully used in situ to test cables in trays, panels and junction boxes, provided that about7,5cm of exposed cable are accessible 4. In accelerated ageing tests, good correlation has been obtained between modulus measurements and elongation at break for polyvinyl chloride (PVC) jacketed cables, chlo
43、rosulphonated polyethylene (CSPE) and a range of elastomers 4 5 6. Examples are shown inFigure 3 andFigure 4 for an ethylene propylene (EPR)/CSPE cable and for an EPR based cable (kerite FR) respectively. The indenter does not appear to be suitable for use with polyolefins and radiation aged PVC bec
44、ause their modulus changes very little with ageing. More recent indenter data indicates that the method may be usable with these materials with a modified technique 7. Limitations: By its very nature, the indenter can only measure the properties of the cable material over a limited area in the vicin
45、ity of the probe. The indenter modulus values obtained can show a marked variation if the jacket thickness is variable, increasing as the thickness decreases. The construction of the cable, for example the presence of armouring or shielding, is also likely to affect the modulus value. Because of thi
46、s, extensive baseline data would be required to cover the range of cable materials and construction types used in a typical power plant. The indenter is limited to those materials which harden or soften significantly during ageing; this includes many of the types of cables used in older plants. In m
47、ost of the cable areas which are accessible to the indenter, only the properties of the jacket material can be measured. Since the jacket materials in most cable constructions tend to degrade more rapidly than the insulation materials, indenter measurements can still give early warning of cable degr
48、adation. 1) Figures in square brackets refer to the bibliography given in Annex A.BS7816-3:1998 BSI 05-1999 3 3.1.2 Sonic velocity This technique is at an early stage of development and at present has only been tested on PVC based cables 6. Sonic velocity testing is based on the fact that the veloci
49、ty of sound in a solid medium is dependent on both the density and the modulus and is given by: where C is the sonic velocity; E is the elastic modulus; is the polymer density. Since both modulus and density can change during ageing of cable materials, changes in sonic velocity would be expected to occur on ageing. The tester uses piezoelectric transducers to transmit and rec
