1、 International Telecommunication Union ITU-T K.77TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(12/2013) SERIES K: PROTECTION AGAINST INTERFERENCE Characteristics of metal oxide varistors for the protection of telecommunication installations Amendment 1: New Appendix III Characterizing
2、thermally protected MOVs using a.c. step stress testing Recommendation ITU-T K.77 (2009) Amendment 1 Rec. ITU-T K.77 (2009)/Amd.1 (12/2013) i Recommendation ITU-T K.77 Characteristics of metal oxide varistors for the protection of telecommunication installations Amendment 1 New Appendix III Characte
3、rizing thermally protected MOVs using a.c. step stress testing Summary Amendment 1 to Recommendation ITU-T K.77 adds a new appendix that describes a general procedure for characterizing the performance of the thermal disconnect of thermally protected metal oxide varistors. History Edition Recommenda
4、tion Approval Study Group Unique ID*1.0 ITU-T K.77 2009-01-13 5 11.1002/1000/9659-en 1.1 ITU-T K.77 (2009) Cor.1 2011-05-05 5 11.1002/1000/11350-en1.2 ITU-T K.77 (2009) Amd. 1 2013-12-13 5 11.1002/1000/12116-en_ *To access the Recommendation, type the URL http:/handle.itu.int/ in the address field o
5、f 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.77 (2009)/Amd.1 (12/2013) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, info
6、rmation 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 issuing Recommendations on them with a view to standardizing telecommunications on a wo
7、rldwide 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 topics. The approval of ITU-T Recommendations is covered by the procedure laid down in
8、 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 “Administration“ is used for conciseness to indicate both a telecommunication admi
9、nistration 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) and compliance with the Recommendation is achieved when all of these mandatory pro
10、visions 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 Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention
11、 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 claimed Intellectual Property Rights, whether asserted by ITU members or others out
12、side 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, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the l
13、atest 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, without the prior written permission of ITU. Rec. ITU-T K.77 (2009)/Amd.1 (12/2
14、013) 1 Recommendation ITU-T K.77 Characteristics of metal oxide varistors for the protection of telecommunication installations Amendment 1 New Appendix III Characterizing thermally protected MOVs using a.c. step stress testing Appendix III Characterizing thermally protected MOVs using a.c. step str
15、ess testing (This appendix does not form an integral part of this Recommendation.) III.1 Introduction This appendix gives details of a general procedure which characterizes the performance of the thermal disconnect of a thermally protected MOV using a.c. step stress testing. III.2 Procedure Figure I
16、II.1 shows the characterization circuit. An a.c. voltage source, US, of 1.6 times the MOV maximum continuous operating voltage (MCOV), UC, is applied to the MOV via resistor RX. Resistor RXdefines the prospective short-circuit current. The prospective short-circuit currents used double with each ste
17、p. The first test is at 0.125 A and the subsequent six steps, using a new sample for each test, are 0.25 A, 0.5 A, 1 A, 2 A, 4 A and 8 A. For step number 1, resistor RXis R1= 8UCand for the subsequent six steps half the resistance value i.e., R2= 4UC, R3= 2UC, R4= UC, R5 = 0.5UC, R6= 0.25UC, R7= 0.1
18、25UC. Each test current shall be applied for a 15-minute period or if the monitored current falls to zero during that time, the test is terminated. KEY US= 1.6UCMOV = Composite symbol of an MOV (resistance dependent on applied voltage, U) and series disconnect (operated by temperature, ) RX= 8UC/(2x
19、1) CT = Current Transformer for monitoring MOV current SW = Switch to apply USFigure III.1 Disconnect characterization circuit MOVRXUSUCTSW2 Rec. ITU-T K.77 (2009)/Amd.1 (12/2013) The test atmospheric conditions used are given in clause 7 Test methods. The thermally protected MOV should be mounted i
20、n accordance with the manufactures recommendations. When mounted the MOV should be surrounded with a cheese cloth tent spaced 10 mm from the MOV body. III.3 Results For each test record the prospective current and the time for disconnection if it occurs. At the end of each test where disconnection o
21、ccurs the cheese cloth should be examined for any damage. Cheese cloth damage would indicate a possible hazardous situation. The test results of prospective current and disconnect time can be plotted in the format shown in Figure III.2. Figure III.2 Example of disconnect prospective current versus t
22、ime characteristic Operate Time - s10 100 1000Prospective Current-A0.1110Printed in Switzerland Geneva, 2014 SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Series D General tariff principles Series E Overall network operation, telephone service, service operation and huma
23、n factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integrated services digital network Series J Cable networks and transmission of television, sound programme and other
24、 multimedia signals Series K Protection against interference Series L Construction, installation and protection of cables and other elements of outside plant Series M Telecommunication management, including TMN and network maintenance Series N Maintenance: international sound programme and televisio
25、n transmission circuits Series O Specifications of measuring equipment Series P Terminals and subjective and objective assessment methods Series Q Switching and signalling Series R Telegraph transmission Series S Telegraph services terminal equipment Series T Terminals for telematic services Series
26、U Telegraph switching Series V Data communication over the telephone network Series X Data networks, open system communications and security Series Y Global information infrastructure, Internet protocol aspects and next-generation networks Series Z Languages and general software aspects for telecommunication systems
