1、 International Telecommunication Union ITU-T K.97TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2014) SERIES K: PROTECTION AGAINST INTERFERENCE Lightning protection of distributed base stations Recommendation ITU-T K.97 Rec. ITU-T K.97 (02/2014) i Recommendation ITU-T K.97 Lightning protection
2、of distributed base stations Summary Recommendation ITU-T K.97 deals with lightning protection of a distributed base station (DBS) on the tower site. A DBS is a new type of radio base station which consists of a remote radio unit (RRU) located on the tower, and a base band unit (BBU) inside the shel
3、ter at the bottom of the tower. Lightning protection of DBS is not fully covered by Recommendation ITU-T K.56. The main objective of this Recommendation is the lightning protection of RRU and rectifier interfaces with direct current (DC) power cable, and bonding of the DBS. Protection of these inter
4、faces is achieved by installing a protection module. Possible protection schemes for such installations are also described. This Recommendation indicates when these protection modules should be used, and provides indication of their withstand current. The surge protective device (SPD) needed on the
5、feeder cable is also indicated. Bonding configurations of the protection module and of the optical fibre cable are also illustrated. Appendix I shows an example of an isolated protection solution. History Edition Recommendation Approval Study Group Unique ID*1.0 ITU-T K.97 2014-02-13 5 11.1002/1000/
6、12130 _ *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.97 (02/2014) FOREWORD The International Telecommunication Union (ITU
7、) 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 issu
8、ing 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 top
9、ics. 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, the expression
10、 “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)
11、 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 Recomm
12、endation 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
13、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 received notice of intellectual property, protected by patents, which may be required to implement this Recomm
14、endation. 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 2014 All rights reserved. No part of this publication may be reproduced, by any means whatsoever,
15、without the prior written permission of ITU. Rec. ITU-T K.97 (02/2014) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviations and acronyms 2 5 Reference configuration 2 6 Protections of DBS . 3 6
16、.1 Protection need . 3 6.2 RRU protection . 4 6.3 Protection of rectifier 7 6.4 The need of feeder SPD 7 7 Bonding of DBS . 7 7.1 Bonding RRU and protection module 7 7.2 DC power cable 8 7.3 Bonding configuration of protection module at rectifier side 9 7.4 BBU bonding 12 7.5 Bonding of optical fibr
17、e cable 13 Appendix I Isolated protection solution: Example . 14 Appendix II Assessment of the energy delivered to clamping type SPC used in RRU protection module . 16 Rec. ITU-T K.97 (02/2014) 1 Recommendation ITU-T K.97 Lightning protection of distributed base stations 1 Scope This Recommendation
18、addresses distributed base stations (DBSs) composed of a shelter or an outdoor cabinet to house equipment, and a nearby tower for antennas and equipment. The tower will prevent lightning from hitting the shelter or outdoor cabinet. The purpose of this Recommendation is to give criteria for the defin
19、ition of procedures that will protect DBSs against lightning discharges. 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 we
20、re 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 currently valid ITU-T Recommend
21、ations 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.27 Recommendation ITU-T K.27 (1996), Bonding configurations and earthing inside a telecommunication building. ITU-T K.39 Recommen
22、dation ITU-T K.39 (1996), Risk assessment of damages to telecommunication sites due to lightning discharges. ITU-T K.40 Recommendation ITU-T K.40 (1996), Protection against LEMP in telecommunications centres. ITU-T K.56 Recommendation ITU-T K.56 (2010), Protection of radio base stations against ligh
23、tning discharges. ITU-T K.85 Recommendation ITU-T K.85 (2011), Requirements for the mitigation of lightning effects on home networks installed in customer premises. IEC 62305-2 IEC 62305-2 ed2.0 (2010), Protection against lightning Part 2: Risk management. 3 Definitions 3.1 Terms defined elsewhere T
24、he definitions contained in the referenced documents apply to this Recommendation. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 base band unit (BBU): The base band module of a radio base station (RBS) which can be installed separated from the remote
25、 radio unit (RRU). NOTE Optical fibre is commonly used to connect the base band unit (BBU) to the remote radio unit (RRU). 3.2.2 cable tray: Rigid structural system used to securely fasten or support cables. 2 Rec. ITU-T K.97 (02/2014) 3.2.3 distributed base station (DBS): One kind of radio base sta
26、tion (RBS), where the remote radio unit (RRU) and the base band unit (BBU) can be installed separated. 3.2.4 radio base station (RBS): Installation intended to provide access to the telecommunication system by means of radio waves. 3.2.5 remote radio unit (RRU): The radio frequency module of a radio
27、 base station (RBS) which can be installed separated from the base band unit (BBU). NOTE 1 Optical fibre is commonly used to connect the base band unit (BBU) to the remote radio unit (RRU). NOTE 2 The radio frequency module is also called remote radio head (RRH). 4 Abbreviations and acronyms This Re
28、commendation uses the following abbreviations and acronyms: AC Alternating Current BBU Base Band Unit DBS Distributed Base Station GDT Gas Discharge Tube MEB Main Earthing Bar MET Main Earth Terminal MOV Metal-Oxide Varistor LPL Lightning Protection Level LPZ Lightning Protective Zone ODF Optical fi
29、bre Distribution Frame RBS Radio Base Station RRH Remote Radio Head RRU Remote Radio Unit RTN Return SPC Surge Protective Component SPD Surge Protective Device 5 Reference configuration Figure 1 shows the reference configuration considered in this Recommendation. In this figure, three lightning prot
30、ective zones (LPZs), as described in ITU-T K.40, can be seen. In Figure 1, RRU is installed very close to the antenna and is, in general, connected to the antenna by a coaxial feeder cable and to BBU by an optical fibre cable. RRU is powered from the rectifier by a shielded or unshielded direct curr
31、ent (DC) power cable. Both optical fibre and DC power cables run along the tower and enter the shelter. Rec. ITU-T K.97 (02/2014) 3 K.97(14)_F01LPZ0AAntennaRRU LPZ0BShelterProtectionmoduleRectifier BBULPZ1Bonding ring conductorFeeder cableDC power cableOptical fibre cableFigure 1 Reference configura
32、tion for a DBS 6 Protections of DBS The main difference between distributed base station (DBS) and traditional radio base station (RBS) is that RRU (RRH) is separately installed from BBU. RRU can be installed very close to the antenna and powered by the inverter located inside the shelter or outdoor
33、 cabinet. Therefore, the emphasis of DBS lightning protection are the RRU and inverter interfaces with DC power cable. The DC power cable to RRU should not be exposed to direct lightning strikes and, therefore, should be located in lightning protection zone LPZ0B. ITU-T K.56 is the basic Recommendat
34、ion that a DBS should comply with. Requirements for DBS protection not included in ITU-T K.56 are described in the following clauses. 6.1 Protection need The protection need shall be evaluated by the risk assessment of loss of services (R2) according to IEC 62305-2. When the risk is greater than the
35、 tolerable risk RT, defined by the network operator, protection measures are necessary. The comparison between the risk and the tolerable risk allows determining the lightning protection level (LPL) that the protection measure at each equipment interface has to withstand to reduce the risk below the
36、 tolerable risk. For the particular application, this Recommendation presents a simplified approach for the evaluation of the protection need based on IEC 62305-2. In this approach, the protection needs can be evaluated by considering the frequency of damage (F), as described in ITU-T K.39 and ITU-T
37、 K.85, instead of the risk of loss of services. In general, the frequency of damage is the sum of the frequencies of damage due to: direct flashes to (FD) and near (FN) the tower, direct flashes to (FSD) and near (FSN) the services entering the DBS. Considering that the protective measures contained
38、 in ITU-T K.56 are applied in the services entering the DBS, the frequency components FSDand FSNcan be neglected. Furthermore, considering the RRU protection module, the damages due to flashes near the tower (FN) are negligible in comparison with damages caused by direct flashes to the tower (FD). T
39、hen: 4 Rec. ITU-T K.97 (02/2014) SPDDDPNFF = (1) where: NDnumber of direct flashes to the tower per year PSPDprotection factor of the protection module When the frequency of damage is greater than the tolerable value (F FT), then protection measures are necessary. The tolerable frequency of damage v
40、alue should be defined by the network operator. For example, FT= 0.05 means that, in average, 1 damage in 20 years (1/20) is acceptable. The number of direct flashes to the tower can be calculated by: gtDNhcN =29 (2) where c exposition factor (equal to 1 for flat ground and 2 for mountain top) httow
41、er height (km) Ngground flash density (flashes km2 year1) The ratio between the tolerable (FT) and expected number of direct flashes to the tower (ND) gives the probability associated with the lightning peak current to be considered (PSPD): DTSPDNFP /=(3) The value of PSPDshall be used in Table 1 in
42、 order to determine the LPL to be considered in the protection design. In doing so, the PSPDvalue calculated by Equation 3 shall be converted to the next lower value in Table 1, e.g., a value PSPD= 0.03 shall be converted to PSPD= 0.02. Table 1 Lightning protection level (LPL) as function of PSPDLPL
43、 I kA PSPDIII-IV 100 0.05 II 150 0.02I 200 0.01SPDs having better characteristics (see IEC 62305-2 Table B.3 for more information). 0.005-0.001 6.2 RRU protection 6.2.1 RRU protection module The protection module of RRU port with DC power cable can be a box outside RRU, or can be a protection circui
44、t inside RRU, as shown in Figures 2 and 3. The SPD protection level should be selected in order to achieve that the effective protection level should be less than the resistibility of the RRU and the rectifier (see clause 8 of ITU-T K.56). K.97(14)_F02ProtectionmoduleRRUDC power cableTowerFigure 2 P
45、rotection module on DC power cable outside RRU Rec. ITU-T K.97 (02/2014) 5 K.97(14)_F03ProtectionmoduleRRUDC power cableTowerFigure 3 Protection circuit integrated inside RRU Possible protection schemes of the protection module are illustrated in Figure 4. Figures 4-a, 4-b and 4-c are suitable for d
46、.c.-I configuration; Figure 4-d is suitable for d.c-C configuration. These configurations are described in ITU-T K.27. K.97(14)_F04a dbc 48 V 48 V 48 V 48 VRTN RTNRTN RTNSPC SPCSPC SPC SPCSPC SPCBonding bar Bonding barBonding bar Bonding barSPCFigure 4 Possible protection schemes of RRU protection m
47、odule 6.2.2 Need of protection module at RRU port with dc power cable When unshielded DC power cable is used where RRU is installed on the tower, the DC protection module upstream RRU (or protection circuit inside RRU) is necessary, as shown in Figure 2 or Figure 3. When shielded DC power cable (or
48、unshielded DC power cable inside a metallic duct along the total length) is used, the shield (or the metallic duct) shall be connected to the tower (or to the metallic shell of RRU) and to the equipotential bonding bar of the BBU shelter or cabinet (see ITU-T K.56). The peak value of the current tha
49、t enters the DC power cable (IDC) can be calculated by: FTLPLDCII = (4) where: ILPLis the peak lightning current associated with the LPL Tis the shielding factor of the tower Fis the shielding factor of the cable tray The values of Tcan be calculated from the tower and cable tray geometry. The approximate values are: Tubular tower (0.5 m radius): T= 0.10 Tubular tower (0.15 m radius): T= 0.30 Three-legged tower: T= 0.20 Four-legged tower: T= 0.15 6 Rec. ITU
