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.108 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2015) SERIES K: PROTECTION AGAINST INTERFERENCE Joint use of poles by telecommunication and solidly earthed power lines Recommendation ITU-T K.108 Rec. ITU-T K.108 (
2、11/2015) i Recommendation ITU-T K.108 Joint use of poles by telecommunication and solidly earthed power lines Summary Recommendation ITU-T K.108 provides protective procedures against accidental contacts between power lines and telecommunication lines, when these lines use the same poles. These proc
3、edures are primarily intended to reduce the risk of an accidental contact (power-cross). However, in the case of a power cross, the protective procedures mitigate its consequences. This Recommendation provides a set of clearance values between power and telecommunication lines at the joint-use pole
4、and the rules for achieving the insulation coordination between the lines. In the case of a power-cross, the earthing and bonding procedures are intended to assure the immediate tripping of the power line circuit breaker. As a backup protection, this Recommendation requires the use of surge protecti
5、ve devices at the customer premises whenever there is a joint-use of poles with medium voltage power lines. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.108 2015-11-29 5 11.1002/1000/12671 Keywords Clearances, earthing, insulation coordination, joint-use of poles, power
6、-cross, power lines. * 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.int/11.1002/1000/11830-en. ii Rec. ITU-T K.108 (11/2015) FOREWORD The International Telecommunica
7、tion 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 que
8、stions 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 Recommendatio
9、ns 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 standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation,
10、 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
11、 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
12、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 claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or app
13、licability 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 imp
14、lement 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 2016 All rights reserved. No part of this publication may be reproduced, by any
15、means whatsoever, without the prior written permission of ITU. Rec. ITU-T K.108 (11/2015) 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 2 5 General considerations 3 6 Pos
16、sible protection approaches . 3 6.1 Integrated protection . 3 6.2 Coordinated protection . 3 7 The power-cross problem . 3 8 Minimum clearances . 4 9 Installation of surge protective devices 5 10 Insulation coordination . 6 10.1 Insulation of the telecommunication cable outer sheath 6 10.2 Insulatio
17、n of splices and distribution boxes . 6 10.3 Insulation between the metallic supporting strand and the pole . 6 11 Bonding and earthing 7 11.1 Bonding 7 11.2 Earthing 8 Appendix I Rationale for the insulation coordination . 10 Bibliography. 12 Rec. ITU-T K.108 (11/2015) 1 Recommendation ITU-T K.108
18、Joint use of poles by telecommunication and solidly earthed power lines 1 Scope This Recommendation provides technical procedures in order to protect the telecommunication lines installed in poles that are also used by solidly earthed power distribution lines, with special reference to the accidenta
19、l contact between these lines (power-cross). For the protection regarding the interference produced by electric power lines on telecommunication lines, the user shall refer to b-ITU-T K.26. The telecommunication lines considered are those made of cables containing one or more twisted metallic pairs
20、with and without a metallic sheath and covered by an outer plastic sheath. These cables are supported by a steel or composite strand that may be incorporated in the same cable or may be independent. In the latter case, the steel strand may be bare or insulated by a plastic outer sheath, and the tele
21、communication cable is attached to the steel strand usually by a lashing wire. The power distribution lines considered are those operating in alternating currents with nominal voltages up to 25 kV (phase-to-phase). The lines may have one, two, or three phases, with and without a neutral conductor. I
22、t is considered that the power transformer at the distribution substation has its windings in the secondary side connected in Y configuration and that the neutral of the transformer (central point of the Y) is connected directly to earth (solidly earthed). Substation power transformers which are sec
23、ondary side-earthed through a resistor, non-earthed, or earthed by resonant systems (e.g., Petersen coil) are out of the scope of this Recommendation. NOTE The distribution substation referred above is the origin of the distribution medium voltage feeders that provide power to the medium voltage / l
24、ow voltage transformers. 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 publication, the editions indicated were valid. All Recommendations and other referenc
25、es 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 currently valid ITU-T Recommendations is regularly published. The reference to
26、a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.20 Recommendation ITU-T K.20 (2015), Resistibility of telecommunication equipment installed in a telecommunications centre to overvoltages and overcurrents. ITU-T K.21 Recommend
27、ation ITU-T K.21 (2015), Resistibility of telecommunication equipment installed in customer premises to overvoltages and overcurrents. ITU-T K.45 Recommendation ITU-T K.45 (2015), Resistibility of telecommunication equipment installed in the access and trunk networks to overvoltages and overcurrents
28、. ITU-T K.65 Recommendation ITU-T K.65 (2011), Overvoltage and overcurrent requirements for termination modules with contacts for test ports or surge protective devices. ITU-T K.66 Recommendation ITU-T K.66 (2011), Protection of customer premises from overvoltages. 2 Rec. ITU-T K.108 (11/2015) IEC 6
29、0060-1 IEC 60060-1 (2010), High-voltage test techniques Part 1: General definitions and test requirements. IEC 61643-21 IEC 61643-21 (2008), Low voltage surge protective devices Part 21: Surge protective devices connected to telecommunications and signalling networks Performance requirements and tes
30、ting methods. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 breakdown voltage b-IEC 60050: Voltage at which electric breakdown occurs under prescribed test conditions, or in use. 3.1.2 insulation coordination b-IEC 60050: Selection of
31、 the electric strength of equipment in relation to the voltages which can appear on the system for which the equipment is intended, and taking into account the service environment and the characteristics of the available protective devices. 3.1.3 low voltage b-IEC 60050: Voltage having a value below
32、 a conventionally adopted limit. NOTE For the distribution of AC electric power, the upper limit is generally accepted to be 1000 V. 3.1.4 medium voltage (MV) IEC 60050-601:2001, 601-01-28: (not used in the UK in this sense, nor in Australia). Any set of voltage levels lying between low and high vol
33、tage. NOTE 1 The boundaries between medium and high voltage levels overlap and depend on local circumstances and history or common usage. Nevertheless the band 30 kV to 100 kV frequently contains the accepted boundary. NOTE 2 The medium voltage is not a standardized term. It is specified as a system
34、 voltage class by IEEE b-Terms. NOTE 3 The preferred medium nominal (line-to-line) voltages in North America: 4.16 kV, 12.46 kV, 13.8 kV, 34.5 kV and 69 kV b-Terms. Typical MV system voltages for public distribution: in Europe 10 kV (mainly underground) 20 kV and 35 kV (mainly overhead) b-Lacroix, i
35、n Japan 6.6 kV. 3.1.5 solidly earthed (neutral) system b-IEC 60050: A system whose neutral point(s) is(are) earthed directly. 3.1.6 withstand voltage b-IEC 60050: Voltage applied to a specimen under prescribed test conditions which does not cause breakdown. 3.2 Terms defined in this Recommendation T
36、his Recommendation defines the following term: 3.2.1 power-cross: line-to-earth short-circuit in a power line whose current path to earth involves a telecommunication line. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: SPD Surge Protective Device VE
37、Phase-to-earth voltage of the power line Rec. ITU-T K.108 (11/2015) 3 5 General considerations Telecommunication operators that wish to use the poles already in use for power distribution lines are recommended, when national laws and regulations permit such an arrangement, to take the following gene
38、ral considerations into account: There are economic and aesthetic advantages to be derived from the joint-use of poles by telecommunication operators and power utilities. When suitable joint construction methods are used, there is, nevertheless, some increased likelihood of danger by comparison with
39、 non-joint-use lines, both to staff working on the telecommunication line and to the telecommunication installation connected thereto. Special training of personnel working on such lines is highly desirable, especially when the nominal power line voltage is above 1 kV. Special formal agreements are
40、desirable between the telecommunication operator and the power utility in the case of joint-use of poles, in order to define responsibilities. Joint-use of poles with power lines having nominal voltages above 25 kV is not recommended. 6 Possible protection approaches In order to protect the telecomm
41、unication lines against the likelihood of accidental contact with the directly-earthed power distribution lines in joint-use of poles (power-cross), there are two distinct approaches, which are briefly described in this clause. 6.1 Integrated protection In this approach, the telecommunication operat
42、or and the power utility develop together a set of procedures to be applied in both networks in order to achieve the desired level of protection against power-crosses. The resulting procedures may involve the joint-use of earthing connections and the bonding between metallic conductors of both lines
43、 (e.g., to bond the telecommunication line supporting strand to the power line neutral conductor). As this approach has to take into account the specificities of both networks, it is not considered in this Recommendation. NOTE This approach is used in North America, based on a comprehensive study th
44、at settled the procedures and responsibilities for both networks. 6.2 Coordinated protection In this approach, the telecommunication operator implements the protection procedures while taking into account some relevant parameters of the power line, but does not integrate its network with the power n
45、etwork. The resulting procedures do not involve the joint-use of earth connections nor the bonding between metallic conductors of both lines. This Recommendation considers this approach, where the characteristics of the power line are used in order to develop the protection procedures of the telecom
46、munication line in joint-use of poles, resulting in a coordinated protection scheme. 7 The power-cross problem The main source of danger in a joint-use installation between telecommunication and solidly earthed power lines is the power-cross, i.e., the accidental contact between the power line and t
47、he telecommunication line. As the power system is directly earthed, a power-cross leads to a very high short-circuit current. The power-cross may take place due to a number of reasons, some of which are summarized below: The clearance between the lines is too small, so that an overload on the power
48、conductor reduces its height (sag) and causes a contact with the telecommunication line installed below. This type of power-cross is more likely to involve low voltage power lines. 4 Rec. ITU-T K.108 (11/2015) The power conductor breaks and falls on the telecommunication line. This type of power-cro
49、ss is more common in rural areas, due to the longer spans used. The power line insulation fails and leads to a current path involving the telecommunication line. The insulation may fail due to several reasons, such as: cracks or pollution on the insulator, objects falling across the insulator (e.g., tree branches), and lightning surges. This type of power-cross is more likely to involve medium voltage power lines installed on conductive poles (e.g., concrete poles with steel framework). Figure 1 shows an exam
