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.110 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2015) SERIES K: PROTECTION AGAINST INTERFERENCE Lightning protection of the dedicated transformer for radio base station Recommendation ITU-T K.110 Rec. ITU-T K.110
2、(12/2015) i Recommendation ITU-T K.110 Lightning protection of the dedicated transformer for radio base station Summary Recommendation ITU-T K.110 addresses lightning protection of the dedicated transformer for a radio base station (RBS). RBSs are usually powered by the local power utility with a de
3、dicated power line operating at medium voltage (e.g., from 10 kV to 20 kV). A dedicated transformer is installed at the RBS for transforming the medium voltage (MV) to low voltage (LV) (e.g., 380 V or 240 V), which is then used to power the RBS. Frequently, the dedicated transformer is installed on
4、a pole, and thus the associated overhead lines (medium and low voltage) have poor earthing conditions. Therefore, these transformers are exposed to lightning effects and, consequently, the power interruptions caused by lightning flashes can severely affect normal operations of the RBS. The main obje
5、ctive of this Recommendation is to reduce the risk of damage to an RBS dedicated transformer due to lightning flashes, which will improve the safety and reliability of the RBS itself and its related equipment. This Recommendation includes the following features: 1) need of protection for dedicated t
6、ransformer; 2) earthing and bonding of transformer and RBS; 3) direct lightning protection for transformers; 4) transformer insulation requirements; 5) MV/LV arresters and LV surge protective devices (SPDs); 6) protection of ancillary facilities. History Edition Recommendation Approval Study Group U
7、nique ID* 1.0 ITU-T K.110 2015-12-14 5 11.1002/1000/12669 * 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.110 (12/2015) FOR
8、EWORD 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 studyin
9、g 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
10、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 standards are prepared on a collaborative basis with ISO
11、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
12、(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 wo
13、rds 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 claimed Intellectual Property Right. ITU takes no position con
14、cerning 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
15、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 2016 All rights reserved. No part of this p
16、ublication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T K.110 (12/2015) 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 acrony
17、ms 3 5 Conventions 3 6 Need for protection . 3 7 Earthing network for transformer and RBS 5 7.1 Basic principles 5 7.2 Common earthing network . 5 7.3 Separated earthing network 5 8 Direct lightning protection 6 9 Transformer insulation level . 6 10 MV/LV arresters requirements . 6 11 MV/LV arrester
18、s installation 7 11.1 Protection schemes . 7 11.2 Bonding of the transformer 8 12 Protection of ancillary facilities 10 12.1 Power meters 10 12.2 Power conductors . 10 Annex A Calculation for lightning risk factors . 12 A.1 Lightning risk analysis . 12 A.2 Calculation examples 13 Appendix I Analysis
19、 on the reasons of lightning damage 15 I.1 Analysis of the processes that may lead to damage . 15 I.2 Reasons for transformer damage 16 I.3 Forward transformation overvoltage (FTO) . 17 I.4 Inverse transformation overvoltage (ITO) 17 Appendix II Selection and installation of MV/LV arresters . 19 II.
20、1 Solidly earthed power distribution systems 19 II.2 Non-solidly earthed power distribution systems 19 II.3 Installation of MV/LV arresters and drop-out fuse 19 Bibliography. 21 Rec. ITU-T K.110 (12/2015) 1 Recommendation ITU-T K.110 Lightning protection of the dedicated transformer for radio base s
21、tation 1 Scope This Recommendation addresses the lightning protection of dedicated transformers used to provide electrical power for radio base stations (RBSs). It contains procedures for earthing, bonding and direct lightning protection of the dedicated transformer, including protection methods for
22、 the associated power lines, requirements for surge arresters (medium voltage (MV) and low voltage (LV) arresters), and protection procedures for ancillary facilities. Transformers used for powering an RBS and other components (i.e., shared transformers) are not covered in this Recommendation. The l
23、ightning protection of these shared transformers is contained in b-ITU-T K.111. 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 indic
24、ated were 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 Re
25、commendations 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.56 Recommendation ITU-T K.56 (2010), Protection of radio base stations against lightning discharges. ITU-T K.97 Recommenda
26、tion ITU-T K.97 (2014), Lightning protection of distributed base stations. ITU-T K.112 Recommendation ITU-T K.112 (2015), Lightning protection, earthing and bonding: Practical procedures for radio base station sites. IEC 60076-3 IEC 60076-3 (2013), Power transformers Part 3: Insulation levels, diele
27、ctric tests and external clearances in air. IEC 60076-4 IEC 60076-4 (2002), Power transformers Part 4: Guide to the lightning impulse and switching impulse testing Power transformers and reactors. IEC 60099-4 IEC 60099-4 (2014), Surge arresters Part 4: Metal-oxide surge arresters without gaps for a.
28、c. systems. IEC 61643-11 IEC 61643-11 (2011), Low-voltage surge protective devices Part 11: Surge protective devices connected to low-voltage power systems Requirements and test methods. IEC 62305-1 IEC 62305-1 (2010), Protection against lightning Part 1: General principles. IEC 62305-2 IEC 62305-2
29、(2010), Protection against lightning Part 2: Risk management. IEC 62305-3 IEC 62305-3, (2010), Protection against lightning Part 3: Physical damage to structures and life hazard. 2 Rec. ITU-T K.110 (12/2015) 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defin
30、ed elsewhere: 3.1.1 continuous operating voltage of an arrester (Uc) IEC 60099-4: Designated permissible r.m.s. value of power-frequency voltage that may be applied continuously between the arrester terminals in accordance with Ur. 3.1.2 non-solidly earthed power distribution systems b-IEC 60050-601
31、: System generally refers to neutral point ungrounded via arc suppression coil or high-impedance to ground. When short-current fault occurs, the system can not constitute a current loop, the fault current is very small, also known as small current grounding system. 3.1.3 rated voltage of an arrester
32、 (Ur) IEC 60099-4: Maximum permissible RMS. value of power-frequency voltage between its terminals at which is designed to operate correctly under temporary overvoltage conditions as established in operating duty tests. 3.1.4 residual voltage of an arrester (Ures) IEC 60099-4: Peak value of voltage
33、that appears between the terminals of an arrester during the passage of discharge current. 3.1.5 solidly earthed neutral system b-IEC 60050-601: System whose neutral point(s) is (are) earthed directly. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 ar
34、rester disconnector: Device for disconnecting an arrester from the system in the event of arrester failure, to prevent a persistent fault on the system and to give visible indication of the failed arrester. NOTE Eliminate the fault current through the arrester during disconnection generally is not a
35、 function of the device. 3.2.2 dedicated transformer: Power transformer used exclusively to provide electrical power to a radio base station. 3.2.3 drop-out fuse: Fuse used in MV power line and distribution transformers for overload and short circuit protection. 3.2.4 earthing network: The part of a
36、n earthing installation that is restricted to the earth electrodes and their interconnections. 3.2.5 heat-blast disconnector: Device that uses the explosion of a component in order to disconnect a circuit and interrupt the current flow. 3.2.6 high current impulse of an arrester: Peak value of discha
37、rge current having a 4/10 impulse shape which is used to test the stability of the arrester on direct lightning strokes. 3.2.7 lightning protection insulator: An insulator body comprising an upper part and a lower part connected series. When subjected to a lightning overvoltage, the nonlinear resist
38、ance of the lower part decreases and the overvoltage is concentrated at the upper part, causing a flashover. After the lightning current is over, the nonlinear resistance of the lower part rapidly rises and limits the flow of power frequency current. 3.2.8 metal-oxide surge arrester without gaps: Ar
39、rester having non-linear metal-oxide resistors connected in series and/or in parallel without any integrated series or parallel spark gaps. 3.2.9 nominal discharge current of an arrester (In): Peak value of lightning current impulse (8/20 s current impulse) which is used to classify an arrester. Rec
40、. ITU-T K.110 (12/2015) 3 3.2.10 non-linear metal-oxide resistor: Part of the surge arrester which, by its non-linear voltage versus current characteristics, acts as a low resistance to overvoltage, thus limiting the voltage across the arrester terminals, and as a high resistance at normal power-fre
41、quency voltage. 3.2.11 series reactor: Device that limits the lightning current flow through a drop-out fuse, in order to avoid its undesired operation. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: EPR Earth Potential Rise FTO Forward Transformation
42、 Overvoltage ITO Inverse Transformation Overvoltage LV Low Voltage MV Medium Voltage RBS Radio Base Station SPD Surge Protective Device 5 Conventions None. 6 Need for protection Power utilities usually protect distribution transformers against lightning induced surges, but not against direct lightni
43、ng flashes. However, a dedicated power transformer used to provide electrical power to an RBS is installed in an environment that is very exposed to direct flashes. The main items that enhance this high exposure include the presence of a tall metallic tower for the RBS, a long overhead power distrib
44、ution line (feeder) and the RBS placement on a hill. Therefore, the dedicated power transformers for RBS presents a number of aspects that need to be considered: earth potential rise (EPR) when lightning strikes the tower; induced overvoltages when lightning strikes the tower; low voltage (LV) and m
45、edium voltage (MV) lines nearby the transformer (within 3 km) may be struck by lightning. This Recommendation considers two possible earthing configurations: 1) The transformer and the RBS share the same earthing network. This configuration is shown in Figure 1 and should be adopted when the distanc
46、e between the transformer and the RBS is shorter than 30 m. When the tower is struck by lightning, the EPR may cause flashover of the line insulation at the nearest pole, and the current flowing through the MV arresters would be very high and would damage the arresters. Moreover, other components of
47、 the power system could also be damaged. 2) The transformer and the RBS have separated earthing network. This configuration is shown in Figure 2, where the distance between the transformer and the RBS is usually longer than 30 m. When the tower is struck by lightning, the EPR will be applied to the
48、LV side of the transformer and may lead to the breakdown of its insulation. Moreover, if not conveniently specified, the lightning arresters may also be damaged. 4 Rec. ITU-T K.110 (12/2015) Figure 1 Reference configuration for earthing network Figure 2 Reference configuration for separated earthing
49、 network The annual total number of flashes (N) to the RBS site is considered in order to determine the required protection level (Basic, Reinforced, or Special) for the RBS site, as shown in Table 1. Annex A presents the procedure for calculating the total number of flashes (N), as a function of the RBS configuration (common or separated earthing network). Rec. ITU-T K.110 (12/2015) 5 Table 1 Determination of the protection level Total annual number of flashes Protection level N 0.5 Basic 0.5
