1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T K.57TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2003) SERIES K: PROTECTION AGAINST INTERFERENCE Protection measures for radio base stations sited on power line towers ITU-T Recommendation K.57 ITU-T Rec. K.57 (09/2003) i ITU-T Recommendation K.57
2、Protection measures for radio base stations sited on power line towers Summary This Recommendation specifies measures to be taken with respect to safety and risk of damage to equipment through earth potential rise, when power line towers are used for locating radio base stations. It also considers t
3、he special lightning protection scheme, which is needed for this type of installation. This is of special concern when power is fed from the low-voltage network, which is the most common situation. Different options are described. Three appendices are attached: Appendix I, titled “Guide on the coord
4、ination of the isolation level required for the power supply circuit and the potential rise of power line towers“, gives information on how to determine the required isolation voltage level due to the EPR at an earth fault in the tower. In Appendix II, titled “Guide on the LV feeding arrangement“, m
5、ore details on the low-voltage feeding options are given. Finally, Appendix III, titled “Characterization and control of the EPR zone of tower earthing and estimation of the minimum length of the junction section“, presents simple calculations for estimation of the EPR for the determination of the l
6、ength of the so-called junction cable. It also shows graphs of the EPR and touch voltage when grading frame earths around the equipment cabinet are installed. Source ITU-T Recommendation K.57 was approved by ITU-T Study Group 5 (2001-2004) under the ITU-T Recommendation A.8 procedure on 6 September
7、2003. ii ITU-T Rec. K.57 (09/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical,
8、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 which, in tur
9、n, 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 and IEC. NOTE
10、 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 (to ensure e.
11、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 words does not s
12、uggest that compliance with the Recommendation 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 e
13、vidence, 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 patents, whic
14、h may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2004 All rights reserved. No part of this publication may be reproduced, by any means wh
15、atsoever, without the prior written permission of ITU. ITU-T Rec. K.57 (09/2003) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions and abbreviations. 1 3.1 Definitions 1 3.2 Abbreviations . 2 4 General 2 4.1 Earth fault characterization of directly earthed power systems 3 4.2 Earth fault cha
16、racterization of non-directly earthed power systems 3 4.3 Earth potential rise (EPR). 3 5 Power supply 4 5.1 Feeding from the LV network 4 5.2 Feeding from a MV network 8 5.3 Feeding from the HV line. 8 6 Requirements on the antenna system 8 7 Telecommunication cables . 9 8 Earthing arrangements 9 9
17、 Installation and maintenance 9 10 Examples of installations 10 Appendix I Guide on the coordination of the isolation level required for power supply circuit and the potential rise of power line towers 12 I.1 Scope of the investigation 12 I.2 Investigated options, parameters 12 I.3 Analysis of the r
18、esults 15 I.4 Estimation of the required isolation level. 29 Appendix II Guide on the LV feeding arrangement . 33 II.1 LV feeding arrangement. 33 II.2 Protection principles. 34 II.3 Selection of the design values for the protection 36 II.4 Options for the feeding of multiple RBSs 37 Appendix III Cha
19、racterization and control of the EPR zone of tower earthing and estimation of the minimum length of the junction section . 40 III.1 Characterization of the zone of EPR of the tower earthing 40 III.2 Control of touch and step voltages by potential PGE. 44 III.3 Estimation of minimum length values 54
20、ITU-T Rec. K.57 (09/2003) 1ITU-T Recommendation K.57 Protection measures for radio base stations sited on power line towers 1 Scope This Recommendation specifies measures to be taken with respect to safety and risk of damage to equipment through earth potential rise, when power line towers are used
21、for locating radio base stations. Special arrangements for lightning protection at these installations are also covered. It considers both the power feeding and the connection to the telecommunication network. It also mentions the risk of disturbances to the transmitting antenna. Lightning protectio
22、n of radio base stations is treated in ITU-T Rec. K.56. 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 Rec
23、ommendations 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 Recommendations is regular
24、ly 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 Recommendation K.8 (1988), Separation in the soil between telecommunication cables and earthing system of power facilities. ITU-T Recommendation K.3
25、3 (1996), Limits for people safety related to coupling into telecommunications system from a.c. electric power and a.c. electrified railway installations in fault conditions. ITU-T Recommendation K.52 (2000), Guidance on complying with limits for human exposure to electromagnetic fields. ITU-T Recom
26、mendation K.56 (2003), Protection of radio base stations against lightning discharges. IEC 61643-1 (2002-01), Surge protective devices connected to low-voltage power distribution systems Part 1: Performance requirements and testing methods. IEC 61643-12 (2002-02), Low-voltage surge protective device
27、s Part 12: Surge protective devices connected to low-voltage power distribution systems Selection and application principles. 3 Definitions and abbreviations 3.1 Definitions This Recommendation defines the following terms: 3.1.1 potential grading earth (PGE): An electrode system laid at small depth
28、around the equipment cabinet(s) for controlling the step and touch voltages. It is bonded to both the tower and the cabinet(s) earth. ITU-T Rec. K.57 (09/2003) 23.1.2 directly earthed power system: HV and MV power systems, whose neutral is connected to earth through a low impedance or directly. 3.1.
29、3 non-directly earthed power system: HV and MV power systems, whose neutral is connected to earth through a high impedance (resistor or inductor), or arc extinguishing (Petersen) coil or isolated. 3.2 Abbreviations This Recommendation uses the following abbreviations: EPR Earth Potential Rise HV Hig
30、h Voltage (Voltage levels exceeding 100 kV a.c.) LV Low Voltage (Voltage levels not exceeding 1000 V a.c.) MOV Metal Oxide Varistor MV Medium Voltage (Voltage levels lying between LV and HV) RBS Radio Base Station SPD Surge Protective Device T-EPR Tower-earthing potential rise Z-EPR Zone of the eart
31、h potential rise 4 General Locating radio base station antennas in power line towers is mainly of interest in rural areas, where there are no tall buildings, where antennas may be installed. At the same time, some precautions have to be taken in order to make the installation safe and not to cause d
32、amage to the equipment. At every power line tower with a radio base antenna, there is a cabinet located near the tower or between the tower legs. This cabinet is sometimes elevated, if possible. The location of the equipment cabinet is not a safety issue, but rather a question of accessibility to th
33、e tower. This cabinet is hosting equipment for transmitting and receiving and has cable connections for power feeding and signal transmission. There is a transformer cabinet for power supply in close proximity to the equipment cabinet or in a dedicated part of the cabinet. The antenna may be mounted
34、 below or above the phase conductors or even above the overhead earth wire(s), if any. The power line may belong to a directly or non-directly earthed power system. There are two phenomena that have to be considered: Earth potential rise in case of earth fault at the tower This problem is treated by
35、 isolating that part of the RBS equipment, which has external metallic connection, against its cabinet and equipment, which is bonded to the tower. Lightning hitting the tower This problem is handled by bonding the above-mentioned parts of the RBS equipment through suitable SPDs in order not to jeop
36、ardize the isolation for EPR. For further information, see II.2. ITU-T Rec. K.57 (09/2003) 34.1 Earth fault characterization of directly earthed power systems When an earth fault occurs in a power system with directly earthed neutral, there will be an earth potential rise, EPR, at the feeding substa
37、tions, and also at the fault location, which may be the tower, where the radio base station is installed. In most cases the EPR will be much higher at the fault location because the equivalent impedance to the earth at this point is much higher than at the substations. For further information, see A
38、ppendix I. 4.2 Earth fault characterization of non-directly earthed power systems When an earth fault occurs in a power system with non-directly earthed neutral, the EPR will be very small due to the small amplitude of the fault current. However, double earth faults may also occur. In that case the
39、fault current will be much higher and result in a substantial EPR at both fault locations. 4.3 Earth potential rise (EPR) When a single earth fault on a power line of a network with directly earthed neutral or a double earth fault on power line(s) of a network with non-directly earthed neutral occur
40、s, a large EPR will appear at the tower, maybe tens of kVs. The EPR, as a general term, involves the two kinds of potential rise as explained in the following. 4.3.1 Tower-earthing potential rise (T-EPR) The tower potential rise is the potential of the earthing (footing) of tower with respect to the
41、 remote earth occurring during earth fault. The amplitude of the T-EPR depends on a number of different factors such as: a) earth fault current amplitude; b) earth resistance of the pole; c) aerial and underground earth wires, if applied; d) distance to the feeding power stations; e) span between th
42、e towers. The factors mentioned in items d) and e) have of secondary importance. NOTE 1 When the power line is equipped with aerial or underground earth wires, the majority of the fault current returns through these wires and only a fraction of the earth fault current flows through the tower footing
43、. The T-EPR can be characterized by the product of that fraction (3I0E) of the zero-sequence component (3I0) of the earth fault current that is passing through the tower footing, and the earthing resistance (R) of the tower, i.e., 3I0ER. The T-EPR may be calculated or preferably measured in order to
44、 determine, whether special arrangements are not needed, which is unusual; see Appendix I. NOTE 2 When the power line is not equipped with earth wires, the whole of the fault current flows through the tower footing. The T-EPR can be calculated by the product of the zero-sequence component (3I0) of t
45、he earth fault current, and the earthing resistance (R) of the tower, i.e., 3I0R. The T-EPR shall be calculated for each given case by considering the actual conditions of the tower holding the base station. 4.3.2 Zone of the earth potential rise (Z-EPR) The zone of the earth potential rise (Z-EPR)
46、is that area surrounding the tower of the power line where earth potential with respect to the remote earth occurs in case of single phase to earth fault, or in case of non-directly earthed network, double earth fault. This potential falls more or less rapidly in the earth (“potential funnel“) as th
47、e distance from the tower footing increases. The magnitude and the way of decrease of the potential depends on the following factors: ITU-T Rec. K.57 (09/2003) 4a) the magnitude of the T-EPR causing the Z-EPR; b) the geometry (size and structure) of the earthing system; c) soil characteristics (geol
48、ogical nature, stratification, etc.). More detailed characterization of the Z-EPR is given in Appendix III. 5 Power supply The RBS equipment may be powered in the following ways: 1) From the LV network through an isolating transformer in order to separate the EPR area from the surrounding: This is m
49、ost commonly used. 2) From a MV power network: In this case you can use the MV/LV transformer as isolation between the EPR area and the surrounding. 3) From the HV power line itself for example through capacitive voltage divider or inductively coupled loop: This method is expensive and hardly used. For further information, see Appendix II. 5.1 Feeding from the LV network Figure 1 shows the arrangement, when the equipment cabinet is powered from the LV network. K.057_F01MVPublic LVnetworkCouplingpointFeeding LV linePower linetowerJunctionpoint(box)Junction
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