1、 STD-ITU-T RECMN K.33-ENGL 177b = Li8b254L ObZb777 37b INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU K.33 (I 0/96) SERIES K: PROTECTION AGAINST INTERFERENCE Limits for people safety related to coupling into telecommunications system from a.c. electric po
2、wer and a.c. electrified railway installations in fault conditions ITU-T Recommendation K.33 (Previously “CCITT Recommendation”) ITU-T K-SERIES RECOMMENDATIONS PROTECTION AGAINST INTERFERENCE For further details, please refer to ITU-T List of Recommendations. STD-ITU-T RECMN K.33-ENGL L99b 48b2591 O
3、bZb981 T24 FOREWORD . The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telec
4、ommunications on a worldwide basis. The World Telecommunication Standardization 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
5、 the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation K.33 was prepared by ITU-T Study Group 5 (1993-1996) and was approved by the WTSC (Geneva, October 9-18, 1996). NOTES 1. telecommunication administration and a recognized oper
6、ating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a 2. follows: The status of annexes and appendices attached to the Series K Recommendations should be interpreted as - - an annexe to a Recommendation forms an integral part of the Recommen
7、dation; an appendice to a Recommendation does not form part of the Recommendation and 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, el
8、ectronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation K.33 (10/96) 1 STD-ITU-T RECMN K.33-ENGL L99b 48b2571 Ob2b982 Yb0 M CONTENTS Scope Establishing limits Admissible currents 3.1 Effects of alternating currents within the frequency
9、 range 15 to 150 Hz . 3.2 Heart current factor . Equivalent circuit for calculating the body current 4.1 General 4.2 Impedances in the equivalent circuit . Determination of limits Admissible limits 6.1 General 6.2 Admissible limits for a typical situation . 6.3 Admissible limits for a severe situati
10、on References . Appendix I . Calculating limiting voltages in a typical situation . Appendix II . Calculating limiting voltages in a severe situation . 11 Recommendation K.33 (10/96) Page 1 1 1 1 2 3 3 4 7 8 8 8 9 9 9 10 - STD-ITU-T RECMN K-33-ENGL 1776 iAb2571 Ub2b783 BT7 SUMMARY This Recommendatio
11、n gives limiting values of voltages on a telecommunications line caused by a fault occurring on a nearby a.c. electric power or a.c. electrified railway line, shows the way these values have been developed and provides guidance on how to calculate limiting values also in cases where the given values
12、 are not applicable. INTRODUCTION This Recommendation is based on experience gained by telecommunications operators over some decades and takes into account the latest findings. In determining a safe admissible voltage, a number of factors may be taken into account. These factors include: - biologic
13、al data; - - - working practice in use. the applicable current paths through the body; the impedances in the circuit; . Recommendation K.33 (10196) 111 - STD.ITU-T RECMN K.33-ENGL L99b m 4b25L ObZb84 733 STD=ITU-T RECMN K-33-ENGL L77b gBb259L Ob2b785 b7T Recommendation K.33 LIMITS FOR PEOPLE SAFETY
14、RELATED TO COUPLING INTO TELECOMMUNICATIONS SYSTEM FROM A.C. ELECTRIC POWER AND A.C. ELECTRIFIED RAILWAY INSTALLATIONS IN FAULT CONDITIONS (Geneva, 1996) 1 Scope This Recommendation concerns safety problems for people coming in contact with telecommunications circuits exposed to the induction of a.c
15、. electric power or a.c. electrified railway lines. This Recommendation considers only short duration induction such as produced by faults on the inducing lines. This Recommendation does not take into consideration: - - - the steady state induced voltages; the admissible voltages for equipment and c
16、ables; the case of energization of the telecommunications line due to contact with an inducing line. This Recommendation does not define safe working practices; however, consideration of working practices is an important part of the method used to define acceptable limiting values. The telecommunica
17、tions operator has to coordinate the limit setting procedure with the use of appropriate working practices. Guidance on working practices which can be applied is given in Volume VI1 of the Directives i. In the normal operation of telecommunications terminal equipment and where relevant Recommendatio
18、ns are applied, the general public are not expected to be exposed to danger from the common mode voltages and currents induced on the lines. 2 Establishing limits For physiological reasons, limiting values to ensure safe working conditions are based on current data as specified in IEC Publication 47
19、9-1, Effects of currents passing through the human body 2. However, for coupling processes as specified in the scope of this Recommendation, it is appropriate to establish limiting values in terms of voltages. 3 Admissible currents 3.1 Effects of alternating currents within the frequency range 15 to
20、 150 Hz The effects of alternating currents within the frequency range 15 Hz to 150 Hz on the human body are considered in IEC 479-1 2. The physiological effects of the current in the path left hand-to-feet are summarized in that Publication under the form of a diagram defining timecunent zones of e
21、ffects of a.c. currents on persons. The diagram is reproduced in Figure 1. The zones in Figure 1 are defined as follows: 0 Zone 1 - normally no perception; Zone 2 - normally no dangerous pathological effect; Zone 3 - normally no organic trouble; Recommendation K.33 (10/96) 1 STD-ITU-T RECMN K-33-ENG
22、L L99b Y8b2591 ObZb98b 5Db 0 Zone 4 - fibrillation probability less than 5%; Zone 5 - fibrillation probability between 5% and 50%; Zone 6 - fibrillation probability higher than 50%. In order to establish voltage limits, the appropriate timelcurrent zones from those given above are to be selected tak
23、ing into account the training of personnel, work instructions and practices, practical experience, and national regulations. For the purpose of this Recommendation, the following timekurrent zones are considered appropriate: - - Zone 4 for a ypical situation; or Zone 3 for a severe situation as spec
24、ified under 6.3. Zone 4 has been chosen for the typical case allowing for the facts that the limits given in IEC 479-1 are conservative estimates and the typical situation given here refers only to experienced and trained telecommunications personnel. 0%. 5%. 50%. 95% 0.1 0.2 0.5 1 2 5 10 20 50 100
25、200 500 1000 2000 5000 10000 Body Current Ib -+ T0506600-94/d01 FIGURE 1K.33 Timekurrent zones of effects of a.c. current (15 to 150 Hz) on human beings 3.2 Heart current factor The curves in Figure 1 are also valid for other paths than the path left hand-to-feet but it is then necessary to introduc
26、e the heart current factor. This factor represents the ratio between the current densities in the heart for the considered path and the path left hand-to-feet when the current flowing in the two paths is of the same magnitude. The current through paths other than left hand-to-feet that represent the
27、 same risk of ventricular fibrillation as that through the path left hand-to-feet as given in Figure 1 can be calculated using the following equation: with: F the heart current factor; Ix Iref the current for a given path; the reference current (for path left hand-to-feet). 2 Recommendation K.33 (10
28、196) STD*ITU-T RECMN K-33-ENGL L99b 48b2571 Ob2b787 442 Current path Left hand to left foot, right foot or feet Both hands to feet The heart current factors as given in IEC 479-1 are reproduced in Table 1. Heart current factor F 1 .o 1 .o TABLE 1K.33 Heart current factor for various current paths Le
29、ft hand to right hand Right hand to left foot, right foot or feet 0.4 0.8 Back to right hand Back to lefi hand Chest to right hand 0.3 0.7 1.3 Chest to left hand Seat to left hand, right hand or to both hands For example, a current of 200 mA hand-to-hand has the same effect as a current of 80 mA in
30、the reference path fi-om left hand-to-feet. 1.5 0.7 4 Equivalent circuit for calculating the body current 4.1 General Figure 2 gives the equivalent circuit for an induced element (i.e. conductor of a circuit, cable screen or cable sheath) of a telecommunication installation being touched. ib , zb T0
31、507480-97/d02 be U FIGURE 2K.33 Equivalent circuit for contact with an induced element Recommendation K.33 (10/96) 3 STD - ITU-T RECMN K.33-ENGL L99b 9 48b257L Ob2b788 389 The parameters appearing in Figure 2 are the following: U voltage between the induced element and the reference earth at the poi
32、nt where the contact happens, calculated according to Volumes II and III of the Directives i; Z, source impedance; zb total body impedance; zib Zbe impedance between the body and the induced element; impedance between the body and earth. 4.2 Impedances in the equivalent circuit 4.2.1 Source impedanc
33、e Z, The source impedance is the common mode impedance of the loop formed by the touched element (conductor, cable sheath or screen) with earth return. The value of the source impedance can be calculated by the method presented in Volumes II and III of the Directives i. A conductor of a telecommunic
34、ation circuit can be isolated from earth (e.g. coaxial tube) or permanently connected to earth through low impedances (e.g. subscriber lines at the exchange end). Earth connections may also appear during operation of gas discharge tubes installed at ends or at intermediate points of the line due to
35、excessive voltage. A metallic cable sheath is usually connected to earth through relatively low impedances either continuously along the line or at one or both ends and some intermediate points. In some cases, cable sheaths without earth connections are used. In the absence of actual data or for gen
36、eral purposes, one of the following values might be chosen: Z, = O !2 for worst case consideration, e.g. short subscriber lines or bare wires; Z, = 180 Q empirical value that is exceeded by 95% of induced circuits. 4.2.2 Total body impedance Zb The total body impedance is a function of touch voltage
37、 and varies from person-to-person. IEC 479-1 2 gives, for different touch voltages and different paths, total body impedances which are not exceeded by more than 5%, 50% and 95% of the population. The total body impedance is the sum of the internal body impedance and the skin impedance. Values of th
38、e total body impedance are given in Table 2 and Figure 3. They are valid for live human beings for the current paths of hand-to-hand or hand-to-foot for large contact areas (50 to 100 cm2) and for touch voltages up to 5000 V. The internal impedance of the body depends on the current path. Figure 4 s
39、hows the internal impedance of the human body for various current paths expressed as a percentage of that related to the path hand-to-hand. The skin impedance depends on the skin status (people working with their hands usually have higher skin impedances than people working in the office), the conta
40、ct pressure and the contact area (the !ewer the area the higher the impedance). 4 Recommendation K.33 (10196) STD-ITU-T RECMN K-33-ENGL L79b 4862593 ObZb989 215 Touch voltage in V TABLE 2K.33 Values for the total body impedance in R that are not exceeded for a percentage of the population of: Total
41、body impedances for various touch voltages 25 50 5% 50% 95% 1750 3250 6100 1450 2625 4375 75 1 O0 1250 2200 3500 1200 1875 3200 125 220 I 700 I 750 7 1550- 1 1125 1625 2875 1000 1350 2125 1000 Asymptotic value 6oooi 5000 - 750 1050 1500 650 750 850 Parameter: percentage of population Touchvoltage U,
42、 O 200 500 700 1000 2000 3000 4000 5000 V T0506620-941d03 FIGURE 3K.33 Statistical values of total body impedances 4.2.3 The impedance depends widely on work practices. If the working practice in use by the operator assures sufficient safety precautions that prevent harmful contacts, this impedance
43、tends to infinity. In the absence of such precautions or when actual data are not available: Impedance between the body and the induced element Zib may be assumed as the extremely unfavourable case. Recommendation K.33 (10/96) 5 6 The numbers indicate the percentage of the impedance of the human bod
44、y for the path concerned. in relation to the path hand-to-hand. The numbers not in brackets refer to the current paths from one hand to the part of the body in question. The numbers in brackets refer to current paths between two hands and the corresponding part of the body. NOTES 1 is 50% of the imp
45、edance from hand-to-hand. 2 The impedance from one hand to both feet is 75% and the impedance from both hands to both feet As a first approximation the percentages are also valid for the total body impedance. FIGURE 4K.33 Internal impedance of the human body as a function of the current path Recomme
46、ndation K.33 (10/96) STD-ITU-T RECMN K-33-ENGL L77b W 48b257L ObZb771 773 H Type and state of shoes 4.2.4 The impedance depends widely on work practices. If the working practice in use by the operator assures isolation fiom earth this impedance tends to infinity. Impedance between body and earth Zbe
47、 Leather sole Elastomer sole The contact between the body and earth is usually made by feet when the operator stands on the earth. In this case the impedance is the sum of the shoe impedance Zsh and the earthing resistance Zss. Wet or damp shoes, hard soil Wet or damp shoes, loose soil Table 3 gives
48、 some examples of values for the shoe impedance. 5 30 0.25 3 TABLE 3K.33 I Dryshoes 1- 3000 I 2000 I The earthing resistance Z, can be calculated as follows: Z, = 1.5 p with: p Z, being the soil resistivity in Q m; and the earthing resistance in R. (4- 1) When the operator works near an earthed cond
49、uctor such as metal constructions, the possibility to touch these earthed conductors should be examined and the impedance between the body and the earth should be determined. 5 Determination of limits For setting limits for the admissible voltage, the following steps should be taken: - define the possible ways to contact the induced telecommunication line according to the work practices and the local conditions; select the possible current path through the body and determine the appropriate heart current factor (see 3.2); determine the appropriate total
