1、 International Telecommunication Union ITU-T K.46TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2012) SERIES K: PROTECTION AGAINST INTERFERENCE Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges Recommendation ITU-T K.46 Rec. ITU-T K.46 (0
2、5/2012) i Recommendation ITU-T K.46 Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges Summary Recommendation ITU-T K.46 gives a procedure to protect telecommunication lines using metallic symmetric conductors (i.e., twisted pair cables) agains
3、t overvoltages and overcurrents imposed on the lines due to nearby lightning flashes. The procedure is based on the representation of the line by a sequence of sections and nodes, and the evaluation of each node exposure to the lightning-induced surges. Based on the node exposure, the ground flash d
4、ensity and the earth resistivity, the annual number of surges above a given voltage level is calculated. If the voltage level considered is the impulse withstand voltage of the node, then the number of surges above this level corresponds to the annual number of damages to the node. This number shall
5、 be multiplied by the loss due to induced surges in order to obtain the risk of failure due to indirect lightning flashes. The highest risk of all nodes is the risk of the line. The risk of failure due to indirect lightning flashes (RZ) can be used in the risk assessment of a larger system to which
6、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 calculated risk (RZ) shall be compared
7、 with the tolerable risk due to indirect flashes (RTi), 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
8、 or equal to the tolerable limit. The appendices are organized as follows: Appendix I provides data on the electrical characteristics of cable shields, Appendix II presents an algorithm to guide the elaboration of software based on this Recommendation, Appendix III presents the calculation of the co
9、llection area for flashes near the line and Appendix IV shows some examples of calculation. History Edition Recommendation Approval Study Group 1.0 ITU-T K.46 2000-12-08 5 2.0 ITU-T K.46 2003-07-29 5 3.0 ITU-T K.46 2008-04-13 5 4.0 ITU-T K.46 2012-05-29 5 Keywords Earthing resistance, lightning-indu
10、ced surges, lightning protection, refraction factor, risk assessment, shielding factor, surge protective device, telecommunication lines. ii Rec. ITU-T K.46 (05/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications,
11、 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 with a view to standardizing telecommunications on
12、 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 Recommendations is covered by the procedure laid do
13、wn 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 conciseness to indicate both a telecommunication
14、 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 Recommendation is achieved when all of these mandator
15、y 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 party. INTELLECTUAL PROPERTY RIGHTS ITU draws atte
16、ntion 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 Rights, whether asserted by ITU members or other
17、s 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, implementers are cautioned that this may not represent
18、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 permission of ITU. Rec. ITU-T K.46 (05/2012) iii
19、 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 4 5 Reference configuration 4 6 General requirements 5 6.1 Impulse withstand voltage levels 5 6.2 Surge protective devices (SPDs)
20、6 6.3 Earthing and bonding . 6 7 Indirect lightning performance of a telecommunication line . 7 7.1 Number of damages and risk assessment . 7 7.2 Tolerable risk 8 8 Node exposure to lightning-induced surges . 8 8.1 Unshielded nodes 8 8.2 Shielded nodes 9 8.3 Effect of surge protective devices 9 Anne
21、x A Environmental factor and installation factor . 11 Annex B Refraction factor 12 Annex C Shielding factor 14 Appendix I Shield resistance of cables with metallic symmetric conductors . 15 Appendix II Algorithm for computer code . 16 Appendix III Collection area for flashes near a telecommunication
22、 line . 17 Appendix IV Examples of calculation 18 IV.1 Italian survey 18 IV.2 Japanese survey 21 IV.3 German survey 23 IV.4 American survey . 26 IV.5 Final remarks 28 Bibliography. 29 Rec. ITU-T K.46 (05/2012) 1 Recommendation ITU-T K.46 Protection of telecommunication lines using metallic symmetric
23、 conductors against lightning-induced surges 1 Scope This Recommendation gives a procedure in order to protect telecommunication lines using metallic symmetric conductors (i.e., twisted pair cables) against overvoltages and overcurrents imposed on the lines due to nearby lightning flashes. Its calcu
24、lation procedure allows the assessment of the expected annual number of damages (NZ) and the risk of damage due to indirect lightning flashes (RZ). The risk of damage due to indirect lightning flashes can be used in the risk assessment of a larger system to which the telecommunication line is a part
25、, 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 (RZ) shall be compared with the tolerable risk due to indi
26、rect flashes (RTi), 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 the tolerable limit. De
27、pending on the users desire, the resistibility of the external port of network terminal equipment (e.g., exchange line card, modem, POTS telephone set, etc.) may or may not be included in the calculation. This decision implies the selection of the appropriate impulse withstand voltage (UW) of the re
28、levant line node and the result shall be limited to the damage caused to the external port of the equipment. However, the protection of other equipment ports (e.g., power port) and of equipment that does not have a direct interface with the line is outside the scope of this Recommendation and should
29、 be evaluated using the risk assessment applied to the exchange or to the customers structure. The protection of persons using telecommunication equipment inside the exchange or the customers structure from dangerous situations caused by touch voltages is outside the scope of this Recommendation and
30、 should be evaluated using the risk assessment applied to the exchange or to the customers structure. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publicati
31、on, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation 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 cu
32、rrently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not 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 te
33、lecommunications installations. ITU-T K.27 Recommendation ITU-T K.27 (1996), Bonding configurations and earthing inside a telecommunication building. ITU-T K.28 Recommendation ITU-T K.28 (2012), Parameters of thyristor-based surge protective devices for the protection of telecommunication installati
34、ons. ITU-T K.47 Recommendation ITU-T K.47 (2012), Protection of telecommunication lines against direct lightning flashes. 2 Rec. ITU-T K.46 (05/2012) ITU-T K.66 Recommendation ITU-T K.66 (2011), Protection of customer premises from overvoltages. ITU-T K.67 Recommendation ITU-T K.67 (2006), Expected
35、surges on telecommunications and signalling networks due to lightning. ITU-T K.72 Recommendation ITU-T K.72 (2011), Protection of telecommunication lines using metallic conductors against lightning Risk management. IEC 62305-2 IEC 62305-2 (2010), Protection against lightning Part 2: Risk management.
36、 3 Definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 conversion factor: Ratio between the line-to-shield voltage and the line-to-earth voltage arriving at the transition from an unshielded section to a shield
37、ed section. 3.2.2 downstream direction: Direction from the first node to the last node of the line. 3.2.3 impulse withstand voltage (UW): Peak value of the maximum common-mode impulsive voltage (10/700 s waveform) that can be applied to an external equipment port or cable insulation without causing
38、damage. 3.2.4 lightning flash near a line: Lightning flash striking close enough to a line so that it may induce dangerous overvoltages on the line. 3.2.5 loss (L): Annual mean amount of loss (humans and goods) consequent to a specified type of damage due to a dangerous event, relative to the total
39、value (humans and goods) of the object to be protected. 3.2.6 loss due to lightning-induced surges (Li): Annual mean amount of loss (to the public and economic value) consequent to damage in a telecommunication line due to lightning-induced surges, relative to the total value of the service (accordi
40、ng to IEC62305-2, Li= Lo). 3.2.7 metallic symmetric conductors: Transmission media consisting of a pair of twisted wires balanced with respect to earth, usually assembled in groups in order to form a telecommunication cable. 3.2.8 node: Point between two sections of a telecommunication line. 3.2.9 n
41、ode exposure: Value assigned to a line node (in km) that represents the exposure of this node to the effects of the lightning-induced voltages. 3.2.10 number of damages (NZ): Expected annual number of damages in the telecommunication line due to lightning-induced surges. 3.2.11 protection factor of
42、SPD (PSPD): Factor taking into account the effect of surge protective device (SPD) installation at a given node. 3.2.12 protection measures: Measures to be adopted in a telecommunication line to reduce its risk of damage. 3.2.13 refraction factor: Ratio between the common-mode surge voltage travelli
43、ng in the line after passing through a discontinuity in its surge impedance and the surge that would travel in the line if there were no discontinuity in its surge impedance. Rec. ITU-T K.46 (05/2012) 3 3.2.14 risk (R): Value of probable average annual loss (humans and goods) due to lightning, relat
44、ive to the total value (humans and goods) of the object to be protected. 3.2.15 risk of damage from indirect flashes (RZ): Risk component related to failure of lines and connected equipment caused by surges induced on the line by indirect lightning flashes. 3.2.16 rural environment: Area with a low
45、density of buildings. “Countryside“ is an example of rural environment. 3.2.17 section of a telecommunication line: Part of a telecommunication line with homogeneous characteristics where only one set of parameters is involved in the assessment of a risk component. 3.2.18 shielded node: Reference po
46、int of the telecommunication line where at least one cable is shielded. A node at the transition between a shielded and an unshielded cable is shielded. 3.2.19 shielded section: Section of the line where the cable is made of one or more pairs of twisted wires balanced with respect to earth, assemble
47、d together and covered by a metallic sheath. 3.2.20 shielding factor: Ratio between the voltage at a point of the line when the shield is present and the voltage at the same point when the shield is absent. 3.2.21 suburban environment: Area with a medium density of buildings. “Town outskirts“ is an
48、example of suburban environment. 3.2.22 surge: Temporary excessive voltage or current, or both, coupled on a telecommunication line from an external electrical source. 3.2.23 surge impedance (Z): Impedance presented by a line section to the surge propagation. It is generally given by the square root
49、 of the ratio between line-to-earth inductance and line-to-earth capacitance. 3.2.24 surge protective device (SPD): A device that is intended to mitigate surge overvoltages and overcurrents of limited durations. It may consist of a single component or have a more complex design, where several functions are integrated. It contains at least one non-linear component. 3.2.25 telecommunication line: Transmission medium intended for communication between equipment that may be located in separate structures, such as a phone line
