ITU-T K.46-2008 使用金属对称导体抗闪电感应电涌的电信线路保护 K系列：干涉保护 Protection of telecommunication lines using metallic symmetric conductors against lightning-induced
I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU U n i o n K.46 (04/2008) SERIES K: PROTECTION AGAINST INTERFERENCE Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges Recommendation ITU-T K.46 Recommendation ITU-T K.46 Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges Summary Recommendation ITU-T K.46 specifies a procedure to protect telecommunication lines using metallic symmetric conductors against overvoltages and overcurrents imposed on the lines due to nearby lightning discharges. The protection procedure is related to the exposure of the line to the effects of nearby lightning discharges, and includes the earthing and bonding of the cable shield and the installation of surge protective devices (SPDs). This Recommendation follows the risk management procedure which requires that the expected risk of damage due to both direct flashes and flashes near a telecommunication line shall be not greater than the tolerable risk. The user shall refer to Recommendation ITU-T K.72 for the risk management procedure. The risk assessment is limited to the failure of insulation of telecommunication lines (buried or aerial cables, shielded or unshielded cables) which can cause the loss of service. The user shall refer to Recommendation ITU-T K.47 for evaluating the expected risk of damage due to direct lightning discharges, either to the line itself or to the structures where the line enters, and, if necessary, in order to select the protection measures to reduce the risk of damage due to direct flashes. Examples of application of this Recommendation are reported in Appendix IV. Source Recommendation ITU-T K.46 was approved on 13 April 2008 by ITU-T Study Group 5 (2005-2008) under Recommendation ITU-T A.8 procedure. Keywords Conventional length, exposure factor, induced overvoltages, installation factor, lightning near a line, node, protection, risk, risk assessment, shielding factor, SPD. Rec. ITU-T K.46 (04/2008) i FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized 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 with 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 Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-T's 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 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 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 party. 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 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, implementers 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 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ii Rec. ITU-T K.46 (04/2008) CONTENTS Page 1 Scope ......................................................................................................