1、STD-ITU-T RECMN K-4D-ENGL L99b 4b2571 Ob32731 738 m INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU K.40 (1 0/96) SERIES K: PROTECTION AGAINST INTERFERENCE Protection against LEMP in centres telecommunications ITU-T Recommendation K.40 (Previously CCITT Re
2、commendation) STD-ITU-T RECMN KSqO-ENGL L79b 48b257L Ob32732 b74 ITU-T K-SERIES RECOMMENDATIONS PROTECTION AGAINST INTERFERENCE For further details, please refir to ITU-T List of Recommendations. STD-ITU-T RECMN K-LiO-ENGL 177b m idb2591 Ob32933 500 m FOREWORD The IT-T (Telecommunication Standardiza
3、tion Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunicatio
4、n Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resol
5、ution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation K.40 was prepared by IT-T Study Group 5 (1993-1996) and was approved by the WTSC (Geneva, 9-18 October 1996). NOTES 1. telecommunication administration and a recognized operating agency. 2. follows: In this Recommendation, the expression
6、“Administration” is used for conciseness to indicate both a The status of annexes and appendices attached to the Series K Recommendations should be interpreted as - - an annex to a Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation does not form part of the
7、Recommendation and only provides some complementary explanation or information specific to that Recommendation. O IT 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, withou
8、t permission in writing from the ITU. Recommendation K.40 (10/96) i 8 STDSITU-T RECMN K.40-ENGL 299b 48b2591 Ob32934 447 CONTENTS Introduction Scope and purpose . References Definitions Reference configuration . Need for protection Protective measure . 7.1 General principles: Lightning Protection Zo
9、nes (LPZs) . 7.2 Earthing 7.3 Bonding: Minimum CBN . 7.4 Cabling routing . Additional protective measures 8.2 Shielding . 8.1 General Appendix I . Simulation of LEMP effects . Test setup Appendix II - Protection management . 11.1 New telecommunications centres . 11.2 Existing telecommunications cent
10、res Bibliography Page 1 1 1 2 2 2 3 3 5 5 7 7 7 7 7 10 10 10 12 11 Recommendation K.40 (10196) STD-ITU-T RECMN K-Liu-ENGL 1996 W 48b257L Ob32735 383 SUMMARY Guidelines for the design of an effective protective system for a telecom structure against LEMP are proposed. The concept of lightning protect
11、ion zones is introduced as a framework where the specific protective measures are merged: earthing, bonding, cable routing and shielding. Information about simulating the LEMP effects and a shopping-list for the protective measures in existing and new buildings are also given. . Recommendation K.40
12、(10/96) 111 STD-ITU-T RECMN K-40-ENGL L79b LiBb2591 Ob3293b 2LT = Recommendation K.40 PROTECTION AGAINST LEMP IN TELECOMMUNICATIONS CENTRES (Geneva, 1996) 1 Introduction This Recommendation is aimed at setting out the installation and testing principles necessary to protect a telecom structure again
13、st Lightning ElectroMagnetic Pulse (LEMP). It focuses on the design of an effective protective system for the telecom structure environment. The installation engineering guidelines that this Recommendation lays down are based on the following standards, produced by IEC TC 81: “Protection of structur
14、es against lightning, Part 1 - General principles” (IEC 1024-1) and “Protection against lightning electromagnetic impulse, Part 1 - General principles” (IEC 13 12-1). The basic principles for protecting a structure against LEMP: earthing, shielding and bonding can be found in Recommendations K.27 an
15、d K.35. if after applying those principles to a structure, the result of the risk assessment as stated in Recommendation K.39 is that additional protective measures should be taken, this Recommendation gives advice on these special measures. A telecom site with antennas at the top or nearby a teleco
16、m site having more risk of damage by a direct lightning stroke, special attention has been paid herewith to these structures. 2 Scope and purpose This Recommendation addresses new and existing structures, such as telecommunication centres, large installations at subscribers premises, remote sites an
17、d gives advice for the design and the installation of protective measures against LEMP in order to reduce damages to the equipment and cabling inside these structures. 3 References The following IT-T Recommendations and other references contain provisions which, through reference in this text, const
18、itute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of th
19、e Recommendations and other references listed below. A list of the currently valid IT-T Recommendations is regularly published. IEC 1024-1-1:1993, Protection of structures against lightning, Part I: General principles - Section I: Guide A - Selection ofprotection levels for lightning protection syst
20、ems. IEC 13 12- 1 : 1995, Protection against lightning electromagnetic impulse, Part I: General principles. IEC 13 12-4: 1995, Application guide for protection against LEW ITU-T Recommendation K.27 (1 996), Bonding con$gurations and earthing inside a telecommunication building. ITU-T Recommendation
21、K.35 (1996), Bonding configurations and earthing at remote electronic sites. IT-T Recommendation K.39 (1996), Risk assessment of damages to telecommunication sites due to lightning discharges. ITU-T Lightning Handbook (1 978), The protection of telecommunication lines and equipment against lightning
22、 discharges. Recommendation K.40 (10/96) 1 STD-ITU-T RECMN K-9O-ENGL L99b 48b259L b32937 L5b m 4 Definitions All terms and definitions already defined in the standard IEC 1024-1 are applicable also for this Recommendation. The following additional terms and definitions apply as well. 4.1 bonding: A
23、measure to establish a direct or indirect (through an SPD) contact between metallic parts. 4.2 CBN: The Common Bonding Network is the principal means for effecting bonding and earthing inside a telecommunications building. It is the set of metallic components that are intentionally or incidentally i
24、nterconnected to form the principal BN (Bonding Network) in a building. These components include: structural steel or reinforcing rods, metallic plumbing, a.c. power conduit, PE (protective conductor), cable racks and bonding conductors. The CBN always has a mesh topology and is connected to the ear
25、thing network (for further information, refer to Recommendation K.27). 4.3 MCBN: The Minimum Common Bonding Network against LEMP configuration required for protection against LEMP at a telecom centre. Additional bonding may be installed to improve the behaviour against LEMP to reduce the risk of dam
26、age. As stated in various clauses of this Recommendation, the efficiency of these enhancements may be estimated with Recommendation K.39. 4.4 LPS: Lightning Protection System. 4.5 LPZ: Lightning Protection Zone. 4.6 currents. It contains at least one non-linear component. surge protection device (SP
27、D): A device that is intended to limit transient overvoltages and divert surge 5 Reference configuration As a reference configuration - that is, to what type of telecommunication environment should the guidelines suggested in this Recommendation be considered - structures with telecommunication towe
28、rs on the roof or adjacent to the structure should be taken into account. In this configuration a direct lightning stroke to the telecommunication tower is the source of the LEMP phenomena. As the lightning current flows through the tower, it creates a strong electromagnetic field; this field couple
29、s with the internal and external cabling of the equipment inside the telecommunication structure, inducing overvoltages and overcurrents that can destroy electronic components of the equipment. A resistive coupling mechanism takes place as well due to the earth potential rise; partial lightning curr
30、ent will flow in the cable screens resulting in voltages between the conductors and the screen. The resistive coupling may cause also a firing of the SPDs installed at the telecom cables entrance, the LEMP disturbance is then propagated through the core of the telecom cable and may cause damages to
31、the cable when the isolating breakdown voltage between shield and core is surpassed, not only in the telecom cables but in a large extent in the mains conductors and may cause problems for mains connected equipment if their resistibility is lower than the protective level given by the mains SPD. See
32、 Figure 1. 6 Need for protection In order to estimate the need of protection of a given structure against LEMP, Recommendation K.39 should be used to evaluate the risk due to direct stroke to the structure itself ( connection between the nng conductor of each floor with vertical bonding conductors,
33、approximating a Faraday cage; the distance between the vertical conductors should not be about 5 m or less; at the ground floor, connection of the ring conductor to the ring earth electrode. - - Figure 5 illustrates the MCBN. Recommendation K.40 (10/96) 5 STD-ITU-T RECMN K-LiO-ENGL L97b = 4Ab257L Ob
34、3274L bA7 Bonding -8- earth electrode electrode if needed T0507150-96/d04 Figure 4LK.40 - Example of meshed earthing Bonding T0507160-%/do5 To earth conductors Figure 5K40 -Minimum common bonding network MCBN 6 Recommendation K.40 (10196) STD-ITU-T RECMN K.40-ENGL 199b 48b2591 Ob32942 513 D 7.4 Cabl
35、ing routing For the reduction of the overvoltages and overcurrents induced on cabling and bonding conductors, it is recommended to reduce the loop dimensions by a close routing of signal and power cabling and bonding conductors. Constraints due to the structure and equipment locations should be take
36、n into account. 8 Additional protective measures 8.1 General The following subclauses propose additional protective measures to those defined in clause 7, that are recommended when the resistibility of equipment interfaces are not defined. 8.2 Shielding Shielding is the basic measure to reduce elect
37、romagnetic interference including magnetic field effects. 8.2.1 The structure In order to improve the electromagnetic environment, all metal parts of significant dimension associated with the structure should be bonded together and to the LPS, i.e. metal skin roofs and facades, metal reinforcement o
38、f the concrete and metal frames of doors and windows. With regard to telecom buildings, shielded and unshielded structures can be found in practice. - Unshielded buildings, e.g. made of wood or bricks, where an internal bonding system should then be installed to distribute equalizing currents among
39、a greater number of conducting objects creating a reference plane for the entire communication installation. - Shielded buildings made of well interconnected reinforced concrete of steel that have excellent shielding qualities and where all the metallic parts shall be utilized as reference for the i
40、nstallation. 8.2.2 The cabling It is recommended to use shielded cables within the volume to be protected. They should be bonded at least at both ends as well as at the LPZ boundaries. Cabling shielding using a low impedance metallic duct connected in several points to the MCBN, provides a strong re
41、duction (about one hundred times) of the induced voltages and currents to levels that the equipment can resist. The metallic duct should be divided in two parts by a metallic septum: in one side the signal conductors are placed, in the other the power cabling and bonding conductors. The metallic duc
42、t should be connected at each floor ring conductor in order to be merged in the MCBN. Appendix I Simulation of LEMP effects - Test setup For the purposes of analytical estimation of current distribution in theLPS and bonded installation, the lightning current source may be considered as a constant c
43、urrent generator injecting a lightning current, consisting of several strokes, into the conductor of the LPS and its bonded installation. This conducted current, as well as the current in the lightning channel causes electromagnetic interferences. Recommendation K.40 (10/96) 7 STD.ITU-T RECMN K.40-E
44、NGL 1996 m 4b2591 b32943 45T In order to measure the induced voltages due to the lightning stroke in a telecom centre, a test surge current as defined inIEC 1024-2, should be fed into the building. The surge generator is connected to a specific point of the building metallic structure, i.e. the cent
45、re pillars, so that the current could be distributed and directed to earth through the parallel paths provided by the metallic structure of the building. The lightning current returns to the generator via the grounding ring and return conductors joined to the ring. Figures 1.1 and 1.2 show that the
46、induced voltage in a measuring loop inside the building depends on the geometry of the current injection circuit. The distance of the return conductor is responsible for the current disibution in the building and therefore also responsible for the induced voltage (Position a). In order to simulate a
47、pproximately the real lightning current distribution, we need to install the return conductor so far that its position does no longer have a significant influence on the induced voltage (Position by c or d). From practical experience, reasonable conditions for flat buildings are: Figure 1.2 d: 1 45“
48、 and d 2 2/3a. For tower-like structures, a reasonable homogeneous current distribution can be obtained by spacing the return conductor fiom the structure in a distance of 2 3 times the diameter of the structure. A single return conductor configuration is suitable to simulate a lightning strike into
49、 an edge or corner of a building, which is in reality the worst case. If several return conductors were used (a spider-like configuration), they shall be installed also in a distance from the roof which is at least 10 times larger than the spacing between the lightning interception wires on the roof (e.g. 2 m above a reinforced concrete sealing, when the reinforced bars are used for lightning current distribution). Otherwise the current distribution in the horizontal part of the building would be governed by these conductors, which would produce unrealistic results. Simulated
