1、 International Telecommunication Union ITU-T K.47TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2012) SERIES K: PROTECTION AGAINST INTERFERENCE Protection of telecommunication lines against direct lightning flashes Recommendation ITU-T K.47 Rec. ITU-T K.47 (05/2012) i Recommendation ITU-T K.47
2、Protection of telecommunication lines against direct lightning flashes Summary Recommendation ITU-T K.47 gives a procedure in order to protect telecommunication lines using metallic components (symmetric pair, coaxial or optical fibre cables) against direct lightning flashes to the line itself or to
3、 structures that the line enters. The procedure is based on the representation of the line by a sequence of sections and the evaluation of the annual number of damages due to direct flashes for each section and for the structures connected to the line. This number shall be multiplied by the relevant
4、 loss in order to obtain the risk of failure due to direct lightning flashes. The sum of the risk of each line section and also the risk associated with the structures connected to the line gives the total risk of the line. The risk of damage due to direct lightning flashes can be used in the risk a
5、ssessment of a larger system to which the telecommunication line is a part, according to IEC 62305-2. The calculated risk can also be used by the line owner (e.g., telecommunication operator) in order to evaluate the need of implementing additional protection measures on the line. In this case, the
6、calculated risk (Rd) shall be compared with the tolerable risk due to direct flashes (RTd), the latter calculated based on Recommendation ITU-T K.72. If the calculated risk is lower than the tolerable limit, the line is adequately protected. Otherwise, it is necessary to implement additional protect
7、ion measures until the risk of damage is lower than or equal to the tolerable limit. Several parts of this Recommendation make reference to the cable sheath breakdown current (Is) and test current (It), so that the assessment of these parameters are given in Annex A and Annex B, respectively. The ap
8、pendices are organized as follows: Appendix I provides some guidance for the evaluation of the expected loss per damage (L), and Appendix II presents a rationale for the protective effect of guard-wires. History Edition Recommendation Approval Study Group 1.0 ITU-T K.47 2000-12-08 5 2.0 ITU-T K.47 2
9、008-04-13 5 3.0 ITU-T K.47 2012-05-29 5 Keywords Direct flashes, direct lightning performance, guard-wire, lightning protection, risk assessment, sand-box test, sheath breakdown current. ii Rec. ITU-T K.47 (05/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations speci
10、alized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them w
11、ith a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Re
12、commendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for
13、 conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Reco
14、mmendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any p
15、arty. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property
16、 Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implem
17、enters are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2012 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written
18、 permission of ITU. Rec. ITU-T K.47 (05/2012) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 3 5 Reference configuration 3 6 Line performance for direct flashes 3 6.1 Annual
19、number of damages 3 6.2 Risk of damage . 4 6.3 Tolerable risk 4 7 Collection area 5 7.1 Aerial cable . 5 7.2 Buried cable 5 7.3 Structure connected to the cable . 5 8 Protection factor . 6 9 Protection factor of cables 7 9.1 Requirements for cable installation 7 9.2 Optical fibre cable 7 9.3 Cables
20、with internal conductors . 8 10 Protective measures applied to the line 9 10.1 To bury an aerial cable . 9 10.2 Guard-wire on buried cable 9 10.3 Overhead ground wire on aerial cable 11 10.4 Installation of SPDs along the line . 12 11 Protective measures applied to the line-structure interface 13 11
21、.1 Tubular shield . 13 11.2 Shielding by parallel conductors 14 11.3 Use of SPDs at structure entrance 15 Annex A Evaluation of the sheath breakdown current (Is) . 17 Annex B Evaluation of the test current (It) . 18 Appendix I Expected loss per damage (L) 21 Appendix II Rationale for the protective
22、effect of guard-wires 22 Bibliography. 25 Rec. ITU-T K.47 (05/2012) 1 Recommendation ITU-T K.47 Protection of telecommunication lines against direct lightning flashes 1 Scope This Recommendation gives a procedure to protect telecommunication lines using metallic components against direct lightning f
23、lashes to the line itself or to the structures that the line enters. Lines made by the following types of cables are covered by this Recommendation. Symmetric cable: Cable with a core made of one or many metallic symmetric pairs, which may have a metallic sheath, and/or a plastic covering, and/or a
24、supporting wire. Coaxial cable: Cable with metallic inner and outer conductors separated by a dielectric, which may have a plastic covering and/or a supporting wire. Optical fibre cable: Cable with optical fibres, which may also have metallic components such as an inner strength member and/or an out
25、er metallic sheath. Its calculation procedure allows the assessment of the expected annual number of damages (Nd) and the risk of damage due to direct lightning flashes (Rd). The risk of damage due to direct lightning flashes can be used in the risk assessment of a larger system to which the telecom
26、munication line is a part, according to IEC 62305-2. The calculated risk can also be used by the line owner (e.g., telecommunication operator) in order to evaluate the need of implementing additional protection measures on the line. In this case, the calculated risk (Rd) shall be compared with the t
27、olerable risk due to direct flashes (RTd), the latter calculated based on ITU-T K.72. If the calculated risk is lower than the tolerable limit, the line is adequately protected. Otherwise, it is necessary to implement additional protection measures until the risk of damage is lower than or equal to
28、the tolerable limit. The protection against direct flashes for equipment connected to the line is not considered by this Recommendation and it should be evaluated using the risk assessment applied to the structure where the equipment is located (i.e., exchange, customers building or remote site). Th
29、e protection of persons using telecommunication equipment inside a structure from dangerous situations caused by direct flashes (e.g., touch voltages) is outside the scope of this Recommendation and should be evaluated using the risk assessment applied to the relevant structure. 2 References The fol
30、lowing ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Rec
31、ommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does no
32、t give it, as a stand-alone document, the status of a Recommendation. ITU-T K.12 Recommendation ITU-T K.12 (2010), Characteristics of gas discharge tubes for the protection of telecommunications installations. ITU-T K.46 Recommendation ITU-T K.46 (2012), Protection of telecommunication lines using m
33、etallic symmetric conductors against lightning-induced surges. ITU-T K.72 Recommendation ITU-T K.72 (2011), Protection of telecommunication lines using metallic conductors against lightning Risk management. 2 Rec. ITU-T K.47 (05/2012) IEC 62305-2 IEC 62305-2 (2010), Protection against lightning Part
34、 2: Risk management. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 shielded cable ITU-T K.46: Group of one or more pairs of twisted wires balanced with respect to earth, assembled together and covered by a continuous metallic sheath.
35、3.1.2 unshielded cable ITU-T K.46: Group of one or more pairs of twisted wires balanced with respect to earth and assembled together without a metallic sheath. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 breakdown voltage (Ub): Impulse breakdown vo
36、ltage between metallic components in the core and the metallic sheath of a telecommunication cable. 3.2.2 failure current (Ia): Minimum peak value of the lightning return stroke current that causes damage in a telecommunication line. 3.2.3 ground flash density (Ng): Average number of lightning flash
37、es to earth per square kilometre per year. 3.2.4 guard-wire: Metallic wire buried above a cable in order to reduce physical damage due to direct lightning flashes to the cable. 3.2.5 lightning protective cable: Special cable with increased dielectric strength, whose metallic sheath is in continuous
38、contact with the soil either directly or by the use of conducting plastic covering. 3.2.6 lightning protective cable duct: Cable duct of low resistivity in contact with the soil (for example, concrete with interconnected structural steel reinforcements or a metallic duct). 3.2.7 loss (L): Annual mea
39、n amount of loss (humans and goods) consequent to a specified type of damage due to a dangerous event, relative to the total value (humans and goods) of the object to be protected. 3.2.8 loss due to direct lightning flashes to the line (Ld): Annual mean amount of loss (service to the public and econ
40、omic value) consequent of damage in a telecommunication line due to direct lightning flashes to the line, relative to the total value of the service. 3.2.9 loss due to direct lightning flashes to the structure (Ls): Annual mean amount of loss (service to the public and economic value) consequent of
41、damage in a telecommunication line due to direct lightning flashes to a structure connected to the line, relative to the total value of the service. 3.2.10 number of damages due to flashes to the line (Nd): Expected annual number of damages in the telecommunication line due to direct lightning flash
42、es to the line. 3.2.11 number of damages due to flashes to the structure (Ns): Expected annual number of damages in the telecommunication line due to lightning flashes to a structure connected to the line. 3.2.12 protection factor (Kp): Factor that quantifies the capacity of a line to receive a dire
43、ct flash without suffering damage. It usually takes into account the effect of protective measures. 3.2.13 risk (R): Value of probable average annual loss (humans and goods) due to lightning, relative to the total value (humans and goods) of the object to be protected. Rec. ITU-T K.47 (05/2012) 3 3.
44、2.14 risk of damage from direct flashes (Rd): Risk component related to failure of lines and connected equipment caused by direct lightning flashes to the line or to the structure connected to the line. 3.2.15 sheath breakdown current (Is): Minimum current flowing in the metallic sheath which causes
45、 breakdown voltages between metallic elements in the cable core and the metallic sheath, thus leading to damage. 3.2.16 striking distance (D): Distance from the line that, when multiplied by 2 by the line length (L) and the ground flash density (Ng) gives the number of direct flashes per year that h
46、it the line. 3.2.17 test current (It): Minimum current injected by arc in the cable sheath that causes a damage due to thermal or mechanical effects. 3.2.18 tolerable risk of damages (RT): Maximum value of risk of damages not requiring additional protective measures. 3.2.19 tolerable risk due to dir
47、ect flashes (RTd): Maximum value of risk that can be tolerated for the line due to direct lightning flashes to the line or to a structure connected to the line. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: GDT Gas Discharge Tube OGW Overhead Ground
48、Wire SPD Surge Protective Device 5 Reference configuration In order to evaluate the risk of line damage (Rd), the line may have to be segmented in such a way that each section has the same characteristics regarding the type of cable installation (aerial or buried), ground-flash density, average soil
49、 resistivity, type of cable, and environment (urban, suburban or rural). It is also important to identify the structures that the line or its branches enter. The value of Rdhas to be evaluated for each section, and the value for the line is the sum of section values, including the values corresponding to discharges to the structures that the line enters. Figure 1 shows an example of a line with different types of cable installation. The risk of damage shall be evaluated for all transmission media of a cable (twisted pair or coaxial
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