1、 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 U n i o n ITU-T K.67 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2015) SERIES K: PROTECTION AGAINST INTERFERENCE Expected surges on telecommunication networks due to lightning Recommendation ITU-T K.67 Rec. ITU-T K.67 (12/2015) i R
2、ecommendation ITU-T K.67 Expected surges on telecommunication networks due to lightning Summary Recommendation ITU-T K.67 allows the assessment of the characteristics (waveshapes and peak values) of the expected lightning surges on metallic telecommunication lines. These characteristics are presente
3、d as a function of the lightning current parameters and the location on the telecommunication network. A set of formulas and tables are provided, alongside the relevant instructions. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.67 2006-02-13 5 11.1002/1000/8737 2.0 ITU-
4、T K.67 2015-12-14 5 11.1002/1000/12673 Keywords Lightning, overcurrent, overvoltage, surge, telecommunication line. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.in
5、t/11.1002/1000/11830-en. ii Rec. ITU-T K.67 (12/2015) 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
6、 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, es
7、tablishes 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-Ts purview, the necessary
8、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
9、 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 equival
10、ents 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 RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claim
11、ed 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 no
12、t 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/IT
13、U-T/ipr/. ITU 2016 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.67 (12/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defin
14、ed in this Recommendation . 1 4 Abbreviations and acronyms 2 5 Conventions 2 6 Reference configuration 2 7 Lightning parameters 3 8 Conducted surges due to direct flashes to a structure . 4 9 Induced surges due to flashes to or near to a structure . 5 10 Direct flashes to telecommunication lines 6 1
15、1 Flashes near telecommunication lines 6 Annex A Formulas for the loop inductances 7 A.1 Mutual inductance between a lightning flash and a loop . 7 A.2 Self-inductance of a loop 7 Appendix I Model to compute the lightning current in a telecommunication line due to a direct flash 8 I.1 Introduction 8
16、 I.2 Aerial line . 8 I.3 Buried line 9 Bibliography. 12 Rec. ITU-T K.67 (12/2015) 1 Recommendation ITU-T K.67 Expected surges on telecommunication networks due to lightning 1 Scope The scope of this Recommendation is to assess the overvoltages and overcurrents due to lightning at different points of
17、 the telecommunication access network, both outside and inside structures, i.e., exchanges, customer premises and remote sites. This Recommendation provides the tools that allow the user to obtain the peak values and waveshapes of the overvoltages and overcurrents. 2 References The following ITU-T R
18、ecommendations 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 Recommendation ar
19、e 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 not give it, as
20、a stand-alone document, the status of a Recommendation. ITU-T K.98 Recommendation ITU-T K.98 (2014), Overvoltage protection guide for telecommunication equipment installed in customer premises. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere:
21、3.1.1 lightning protection level (LPL): b-IEC 62305-1 Number related to a set of lightning current parameters values relevant to the probability that the associated maximum and minimum design values will not be exceeded in naturally occurring lightning. NOTE Lightning protection level is used to des
22、ign protection measures according to the relevant set of lightning current parameters. 3.1.2 surge: b-ITU-T K.46 Temporary excessive voltage or current, or both, coupled on a telecommunication line from an external electrical source. 3.2 Terms defined in this Recommendation This Recommendation defin
23、es the following terms: 3.2.1 front time or rise time (T1): The front time or rise time of an impulse voltage is defined as 1.67 times the time interval between the instants when the impulse is 30% and 90% of the peak value. The front time of an impulse current is defined as 1.25 times the interval
24、between the instants when the impulse is 10% and 90% of the peak value. 3.2.2 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
25、 integrated. 3.2.3 time to half value (T2): The time to half value of an impulse voltage or current is the time interval between the virtual origin and the first instant at which the voltage or current has decreased to half the peak value. NOTE The virtual origin of an impulse voltage or current is
26、the instant preceding that at which the voltage or current is 30% or 10% of the peak value by a time equal to 0.3 T1 or 0.1T1 respectively. 2 Rec. ITU-T K.67 (12/2015) 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: LPL Lightning Protection Level MDF M
27、ain Distribution Frame MET Main Earthing Terminal SPD Surge Protective Device 5 Conventions The keywords “is required to“ indicate a requirement which must be strictly followed and from which no deviation is permitted if conformance to this Recommendation is to be claimed. The keywords “is recommend
28、ed“ indicate a requirement which is recommended but which is not absolutely required. Thus this requirement need not be present to claim conformance. The keywords “is prohibited from“ indicate a requirement which must be strictly followed and from which no deviation is permitted if conformance to th
29、is Recommendation is to be claimed. The keywords “can optionally“ indicate an optional requirement which is permissible, without implying any sense of being recommended. This term is not intended to imply that the vendors implementation must provide the option and the feature can be optionally enabl
30、ed by the network operator/service provider. Rather, it means the vendor may optionally provide the feature and still claim conformance with this Recommendation. 6 Reference configuration Figure 1 shows the reference configuration for the telecommunication lines, where the nodes indicated have the f
31、ollowing descriptions: Node L: Transition between exchange equipment and external cabling. Node E: Entrance of the exchange building, e.g., the main distribution frame (MDF). Node P: Transition between paper-insulated and plastic-insulated buried cables. Node C: Transition between buried and aerial
32、cables. Node D: Transition between shielded and unshielded aerial cables. Node S: Entrance of the customers building. Node A: Transition between customer equipment and external cabling. Node M: Transition between exchange equipment and internal cabling. Node I: Transition between customer equipment
33、and internal cabling. Rec. ITU-T K.67 (12/2015) 3 Figure 1 Reference configuration 7 Lightning parameters The use of equipment with suitable characteristics is necessary in order to achieve equipment protection and limit its risk of damage. The inherent resistibility requirements of telecommunicatio
34、n equipment used at different points of telecommunication networks have been defined in b-ITU-T K.20, b-ITU-T K.45 and b-ITU-T K.21 for equipment installed in the exchange building, in the access network and in the customers building, respectively. The inherent resistibility allows the equipment to
35、withstand the majority of the induced surges caused by lightning. Because these surges are the most frequent, the use of additional protective measures (primary protection) is limited to the “exposed“ installations, which are determined according to b-ITU-T K.46 and b-ITU-T K.47. The use of primary
36、protection prevents excessive energy from reaching vulnerable parts of the telecommunication installations. Therefore, the rating of primary protectors shall be determined for a low-probability lightning flash, which is done by the selection of the appropriate lightning protection level (LPL) and it
37、s associated probability. These low-probability lightning parameters are given in Table 1 which has been adapted from b-IEC 62305-1. The data contained in Table 1 should be used for assessing the rating of primary protectors. For other assessments, the data related to the most common negative flashe
38、s should be used. With this aim, the parameters of the common negative first strokes and subsequent strokes according to b-Electra 69 are given in Table 2. These parameters are based on a comprehensive set of measurements and according to a recent study from Cigr b-Cigr TB549, they represent the mos
39、t reliable set of data of lightning parameters. 4 Rec. ITU-T K.67 (12/2015) Table 1 Parameters of return stroke currents according to b-IEC 62305-1 Current parameters Symbol Unit LPL (probability of being exceeded) I (1%) II (2%) III (5%) IV (5%) Positive first stroke Peak value Ip kA 200 150 100 Wa
40、veshape T1/T2 s/s 10/350 Negative subsequent stroke Peak value Ip kA 50 37.5 25 Rate of rise di/dt kA/s 200 150 100 Waveshape T1/T2 s/s 0.25/100 Table 2 Parameters of return stroke currents from negative flashes according to b-Electra 69 Current parameters Symbol Unit Probability of being exceeded 9
41、5% 50% 5% First stroke Peak value Ip kA 14 31 69 Front time T1 s 1.8 4.5 11 Time to half value T2 s 30 75 200 Subsequent stroke Peak value Ip kA 5.2 12 29 Front time T1 s 0.1 0.6 2.8 Time to half value T2 s 6.5 32 140 Rate of rise di/dt kA/s 10 40 162 8 Conducted surges due to direct flashes to a st
42、ructure The conducted surges due to direct flashes to a structure are relevant in order to assess the currents delivered at the entrance of the structures (Nodes E and S in Figure 1). The rationale for this assessment is described hereafter. The lightning current of a direct flash to a structure flo
43、ws into the earthing system of the structure as well as into the services connected to structure. Therefore, part of the lightning current enters the conductors of the telecommunication cable directly or via surge protective devices (SPDs) connected to them. As a first approximation, it is assumed t
44、hat 50% of the lightning current (I), flows into the earthing system and the remaining 50% is shared between the n services connected to the structure. The waveform of the surge current is assumed to be equal to that of the lightning stroke current. If the telecommunication line is unscreened and is
45、 not routed into a metallic conduit, each of the m conductors of the line carries an equal part (If), of the peak lightning current, which may be evaluated by: Rec. ITU-T K.67 (12/2015) 5 mn IIf 5.0for an unshielded line (1) For shielded lines or for those routed into a metallic conduit, it is assum
46、ed that the shield or the conduit is bonded to the structure earthing system. Therefore, the peak value (If) of the current entering each one of the m conductors is given by: cssf RRmn RII 5.0 for a shielded line (2) where: Rs = resistance for unit length of the shield or the metallic conduit Rc = r
47、esistance for unit length of the conductor n = number of services connected to the structure m = number of conductors of the telecommunication line. The voltage between a conductor and the main earthing terminal (MET) is approximately given by the product of the earthing resistance to half of the li
48、ghtning current. The magnitude of this voltage is likely to be sufficiently high to operate the primary protection or to cause breakdown of the conductor insulation, if there is no primary protection. Therefore, detailed procedures for calculating the peak voltage are not considered. 9 Induced surge
49、s due to flashes to or near to a structure A lightning flash to or near to a structure induces common mode surges into the loops formed by the telecommunication line inside the structure. These surges would stress the equipment connected to the nodes E, L, M, S, A and I of the reference configuration shown in Figure 1. For a relatively close flash and a short loop, the peak value Voc of the induced open circuit voltage is given by: dtdiMoc LV (3) where: LM = the mutual inductance between the induced loop an
