1、 STD-ITU-T RECMN K-LO-ENGL 1996 m 4b257L Ob328bb 07b = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU K.10 (1 0196) SERIES K: PROTECTION AGAINST INTERFERENCE Low frequency interference due to unbalance about earth of telecommunication equipment ITU-T Reco
2、mmendation K.1 O (Previously CCITT Recommendation) ITU-T K-SERIES RECOMMENDATIONS PROTECTION AGAINST INTERFERENCE For further details, please refer to TU-T List of Recommendations. STD-ITU-T RECMN K-LU-ENGL 177b m 48b259L Ob328b 949 D FOREWORD The IT-T (Telecommunication Standardization Sector) is a
3、 permanent organ of the International Telecommunication Union (IT). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization
4、Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the IW-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsin
5、ki, March 1-12, 1993). IT-T Recommendation K.10 was revised by ITU-T Study Group 5 (1993-1996) and was approved by the WTSC (Geneva, 9-18 October, 1996). NOTES 1. telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for c
6、onciseness to indicate both a 2. follows: The status of annexes and appendices attached to the Senes K Recommendations should be interpreted as - - an annex to a Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation does not form part of the Recommendation and
7、only provides some complementary explanation or information specific to that Recommendation. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in wr
8、iting from the ITU. Recommendation K.10 (10/96) i STD-ITU-T RECMN K-LO-ENGL L77b 48b257L Ob328b9 885 D CONTENTS Introduction Scope Reference texts . Definitions 4.1 Reference circuit representation . Unbalance test 5.1 Test arrangement 5.2 Testing conditions . 5.3 Measurements . Admissible values Pr
9、otection against effects of unbalance of equipment Appendix I . Disturbing mechanisms . Origin of noise effects Conversion mechanism at the input of an equipment . I . 1 1.2 11 Recommendation KA0 (10/96) Page 1 1 1 2 2 3 3 4 5 6 7 7 7 8 STDSITU-T RECMN K-LO-ENGL L79b 48b257L Ob32870 5T7 W SUMMARY Th
10、is Recommendation gives limiting values of unbalance about earth of telecommunication equipment for the domain of the low fiequency band (below a few tens of kHz), presents methods of measurements permitting characterization of the effects of unbalance and provides information about the choice of re
11、levant means of protection. Recommendation K.10 (10/96) . 111 - - STD*ITU-T RECMN K-lU-ENGL 199b = 4Bb257L Ob32871 433 D Recommendation K.10 LOW FREQUENCY INTERFERENCE DUE TO UNBALANCE ABOUT EARTH OF TELECOMMUNICATION EQUIPMENT (Mar del Plata, 1968; revised in 1984, 1993, 1996) 1 Introduction When a
12、 telecommunication installation located in an electromagnetic environment presents an unbalance of impedances about a reference conductor (earth, common conductor), it exposes the network not only to noise effects disturbing the useful signals (reception aspect) but also to radiating phenomena able
13、to disturb other telecommunication installations placed in the vicinity (emission aspect). From this point of view, the balance constitutes a fundamental aspect of quality which is necessary for the electromagnetic compatibility of networks. This Recommendation presents methods of measurement permit
14、ting characterization of the effects of unbalance and also gives some information about the choice of relevant means of protection. The user will find in Appendix I some theoretical tools useful for the analysis of unbalanced equipment. In addition, information is given in several other ITU-T public
15、ations concerning the theory of disturbing mechanisms, the definitions of unbalance parameters and some principles of measurement i and 2. 2 Scope This Recommendation covers the domain of the low fiequency band extending from the fundamental frequency (16 213 Hz, 50 Hz, 60 Hz) and its harmonics, gen
16、erated by the electrical power and traction systems, up to higher frequencies (up until a few tens of kHz) generated by any other industrial or domestic electrical equipment. In this frequency range and considering a normal situation (very low unbalance), the emission effects due to unbalance are ne
17、gligible. Consequently, this Recommendation will consider only the reception aspect of unbalance as the conversion from common mode to differential mode process. Considering the low fiequency band, the typical equipment under study will be the terminating equipment connected at the ends of lines, su
18、ch as the interfaces in exchange and the subscribers terminal including indoor cabling. The cables will not be taken into consideration, due to the fact that they present a balance much higher than that normally found in equipment. Furthermore, ISDN equipment is not covered by this Recommendation. T
19、he methods of measurement presented in this Recommendation refer to the field of testing in the laboratory and some aspects of maintenance activities. 3 Reference texts The following IT-T Recommendations and other references contain provisions which, through reference in this text, constitute provis
20、ions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommenda
21、tions and other references listed below. A list of the currently valid IT-T Recommendations is regularly published. il ITU-T Directives, Volumes II, III, VI and IX. 2 CCITT Recommendation 0.9 (1988), Measuring arrangements to assess the degree ofunbaiance about earth. 31 ITU-T Recommendation G.117 (
22、1996), Transmission aspects of unbalance about earth. Recommendation K.10 (10/96) 1 41 FI 4 4.1 r Termination i, A/ $ “d T T STD-ITU-T RECMN K-LO-ENGL L99b = 48b259L Ob32872 37T Termination B _-_-_-_ Differential mode path J _ - ITU-T Recommendation G.7 12 ( 1996), Transmission performance character
23、istics of pulse code modulation. ITU-T Recommendation 4.552 (1996), Transmission characteristics at 2-wire analogue interfaces of digital exchanges. Definit ions Reference circuit representation Figure 1 gives a general representation of a telecommunications circuit showing the different transmissio
24、n paths involved in the noise generation mechanism. L Common mode path Common return conductor or reference conductor TO5071 SUWd01 common mode voltage u1 +u2 u, = - 2 if = i, + i, common mode current ud = u, - ui differential mode voltage Figure 1K10 - General representation of a disturbed system 4
25、.2 such a circuit is totally unsymmetric. longitudinal path: The term longitudinal path is applied to any loop with reference earth return. By definition, 4.3 common mode path: The common mode path shown in Figure 1 is made of the two wires of a symmetrical pair with a reference conductor. In case o
26、f a cable line with a metallic sheath, the analysis of the problem of interference generally needs to distinguish two circuits: i) The external longitudinal loop (see 4.2) formed by the sheath and the external return (earth). 2) The internal common mode loop formed by a pair with its terminations an
27、d the common mode return (sheath). 4.4 reference plane (earth). It causes the same potential to appear on both conductors relative to the common reference. common mode interference: Interference appearing between both conductors of a pair and a common 2 Recommendation K.10 (10196) - STD-ITU-T RECMN
28、K-LU-ENGL L77b 4862593 UblZ73 2Db m 4.5 common mode voltage and current: voltage: The mean of the phasor voltages appearing between each conductor and a specified reference, usually earth or local zero voltage reference points (refer to Figure i). current: The sum of the phasor currents flowing in a
29、ny two or a specified set of active conductors (refer to Figure i). 4.6 shunt admittance of a pair to the reference conductor (internal or external). common mode parameters: The series impedance of a pair with reference to the return conductor and the 4.7 of one or more conductor(s) and return path,
30、 usually earth or local zero voltage reference points. longitudinal electromotive force (emf, ELI): A source or a phasor sum of sources acting in a loop composed 4.8 differential mode voltage and current: voltage: The voltage between any two of a specified set of conductors, usually a symmetrical pa
31、ir. current: The current flowing in any two or a specified set of conductors, usually a symmetrical pair. 4.9 applied to an unbalanced circuit produces a differential mode signal (noise). conversion from common mode to differential mode: The process by which the common mode interference 4.10 unbalan
32、ce about reference conductor: The unbalance about reference conductor (earth or any other reference conductor) is the difference between the common mode parameters of the different paths of transmission loop. The unbalance may be characterized by a difference between series impedances or shunt admit
33、tances. The term balance is generally used as a factor of quality of the installation regarding the unwanted effects of conversion. 4.11 longitudinal conversion loss (LCL): LCL is defined in Recommendation 0.9 as the ratio expressed in decibel, of the value of electromotive force impressed in the lo
34、ngitudinal path and the value of the differential mode voltage appearing at the input port of the equipment under test (refer to Figure 2). LCL = 20 * Log10 (E:) - dl3 (applicable for one or two ports network) When the measurement is made under real conditions, the longitudinal conversion loss is de
35、noted LCLR (see 5.3.2). 4.12 longitudinal conversion transfer loss (LCTL): LCTL is defined in Recommendation 0.9 as the ratio expressed in decibel, of the value of electromotive force impressed in the longitudinal path and the value of the differential mode voltage appearing at the output port of th
36、e equipment under test (refer to Figure 2). LCTL 20 . Loglo E;:) - dE3 (applicable for two port network only) 4.13 transmission centre) or a piece of transmission or terminal equipment. equipment under test (EUT): The equipment under test may be a line interface in an exchange (or More particularly
37、the term “equipment” will designate an interface circuit connected at the end of a cable. 5 Unbalance test 5.1 Test arrangement The test of the effects of unbalance of a two port equipment can be made in accordance with Figure 2. In the case of a one port equipment, the termination 2 is included ins
38、ide the EUT. Recommendation K.10 (10/96) 3 Termination 1 represents the induced source with an appropriate common mode generator and terminating impedances for both common and differential modes, e.g. induced line with its remote termination. Zdl EUT Termination i Termination 2 . * . , Coupling netw
39、ork Equipment Under Test I Ud2 , / Zd, Zd, differential mode impedance of terminations Z, Z, E, u, IC Ud, Ud, differential mode voltages at the input port and output port of the EUT respectively common mode impedance of the termination i (disturbing source) common mode impedance of temination 2 dist
40、urbing longitudinal emf impressed at the input of EUT common mode voltage applied at the input of EUT current flowing in the common mode circuit Figure 2K10 -General method for testing the effects of unbalance of equipment 5.2 Testing conditions 5.2.1 Parameters Testing Device: It should not noticea
41、bly affect the equipment under test. Coupling network: It can be realized by a centre tapped coil or any other equivalent circuit having the same function. Such a circuit should have balance much better than the equipment. It must not noticeably affect the values of the differential mode impedances
42、of the circuit. Udl, Ud2: The differential mode signals should be measured with an apparatus which will not affect the balance of the whole circuit under test. Terminations: The terminations shall represent the common mode and differential mode impedances as close as possible to the real impedances
43、connected at the end of the equipment. Zdl, Zd2: The differential mode impedances will generally be identified as the characteristic impedance relevant to the measuring frequency. ZL1: The common mode impedance of the induced source will be determined according to the specifications of Recommendatio
44、n 0.9 (see 5.3.1) or by measurement under real operational conditions (see 5.3.2). A comparison of the two methods is included in 5.3.2. 4 Recommendation KI0 (10196) ZLZ: The common mode impedance characterizing termination 2 shall be determined either by calculation or measurement. ELI: The longitu
45、dinal emf provided by the induced source shall be estimated according to the principles given in 5.2.2. 5.2.2 Identification of parameters for measurement under real operational conditions The parameters ELI and ZL, which characterize the disturbing generator, can be estimated by theoretical calcula
46、tions, but such an approach remains a complex task due to the large number and variability of the parameters involved in the whole process of noise effects. A more practical approach is measuring such parameters in the field with real disturbing environments. These measurements should be made in a l
47、arge enough number to perform a statistical treatment in order to obtain values representative of the environment. In order to achieve this, the common mode parameters ELI and ZL shall be measured according to Thvenins principle and under a real configuration of communication. Figure 3 gives an exam
48、ple of the measurement of Thvenins parameters. Pair under study Multipair cable exposed to induction Other Z terminating - equipment I /,/ Other Pairs 2 common mode impedance characterizing the remote termination connected at the pair under study TO50721 QWdO3 Figure 3K.10 - Characterization of the
49、equivalent disturbing generator 5.3 Measurements 5.3.1 LCL measurement with a test bridge (Recommendation 0.9) In case of measurement with a test bridge as specified in Recommendation 0.9, the common mode impedance ZL is equal to a quarter of the differential mode impedance of the termination (typically ZL = 150 ohm). The value LCL indicates the conversion to the differential mode voltage only for that condition when the disturbing source has a low common mode impedance (e.g. a long c
