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.126 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2017) SERIES K: PROTECTION AGAINST INTERFERENCE Surge protective component application guide High frequency signal isolation transformers Recommendation ITU-T K.126
2、Rec. ITU-T K.126 (07/2017) i Recommendation ITU-T K.126 Surge protective component application guide High frequency signal isolation transformers Summary Failures of Ethernet local area network (LAN) ports have been attributed to the use of inappropriate surge protective devices (SPDs), lack of insu
3、lation coordination and inappropriate wiring, which causes the failure of transformers, associated wiring, components and connectors. Recommendation ITU-T K.126 discusses isolation transformer parameters and how they influence the equipment common-mode and differential-mode surge performance. Access
4、 to the full text of Recommendation ITU-T K.95 is necessary to fully understand this Recommendation. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.126 2017-07-29 5 11.1002/1000/13280 Keywords Characteristics, common-mode surge, differential-mode surge, Ethernet, high fre
5、quency, isolation transformer, power over Ethernet, PoE, ratings, surge protective device, SPD. * 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
6、-en. ii Rec. ITU-T K.126 (07/2017) FOREWORD 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
7、 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 worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topic
8、s 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 WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepa
9、red on a collaborative basis with ISO 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
10、 contain certain mandatory provisions (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 ex
11、press requirements. The use of such words 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 Pro
12、perty Right. ITU takes no position concerning 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 o
13、f intellectual property, protected by 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 2017
14、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.126 (07/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recomme
15、ndation . 2 4 Abbreviations and acronyms 3 5 Conventions 3 6 Component construction . 4 6.1 Transformer basics . 4 6.2 Transformer parasitics 4 6.3 Transformer core saturation . 5 6.4 High frequency signal transformers . 6 7 Characteristics . 8 7.1 Measurement 8 7.2 Inter-winding capacitance 8 7.3 I
16、nsulation resistance . 9 7.4 Core saturation voltagetime value 10 7.5 Winding resistance . 11 7.6 Saturated core secondary winding inductance . 11 8 Ratings 12 8.1 Verification . 12 8.2 Rated impulse voltage 12 8.3 Rated winding d.c. 13 9 Application examples . 14 9.1 Transformer example 14 9.2 Comm
17、on-mode surge . 14 9.3 DC insulation resistance . 17 9.4 Differential-mode primary winding surge 18 9.5 Rated impulse voltage 23 9.6 Rated winding d.c. 24 Annex A Use of isolating transformers for a.c. power and signal applications 25 A.1 Application of LITs to equipment that requires isolation 25 A
18、.2 Application of LITs on communication line for high-speed signal transmission 25 A.3 LITs for equipment with low resistibility . 26 Bibliography. 27 Rec. ITU-T K.126 (07/2017) 1 Recommendation ITU-T K.126 Surge protective component application guide High frequency signal isolation transformers 1 S
19、cope The b-ITU-T K.96 application overview guide and other ITU-T component specific guide Recommendations cover surge protective components (SPCs) used in power and telecom surge protective devices (SPDs) and equipment ports. This application guide on high frequency signal isolation transformer tech
20、nology SPCs covers: component construction; characteristics; ratings; application examples. 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 ed
21、itions indicated 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 va
22、lid ITU-T Recommendations 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.95 Recommendation ITU-T K.95 (2016), Surge parameters of isolating transformers used in telecommunication devi
23、ces and equipment. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 clearance b-IEC/TR 60664-2-1: Shortest distance in air between two conductive parts. 3.1.2 common-mode surge ITU-T K.95: Surge appearing equally on all conductors of a g
24、roup at a given location. NOTE 1 The reference point for common-mode surge voltage measurement can be a chassis terminal, or a local earth/ground point. NOTE 2 Also known as longitudinal surge or asymmetrical surge. 3.1.3 creepage distance b-IEC/TR 60664-2-1: Shortest distance along the surface of a
25、 solid insulating material between two conductive parts. 3.1.4 designation of an impulse shape b-IEC 60099-4: Combination of two numbers, the first representing the virtual front time (T1) and the second the virtual time to half-value on the tail (T2). NOTE 1 It is written as T1/T2, both in microsec
26、onds, the sign “/“ having no mathematical meaning. NOTE 2 Some standards use alternative designations such as A/B or T1 T2. NOTE 3 Combination wave generators have both voltage and current impulse designations given separated by a hyphen e.g., 1.2/50-8/20. 2 Rec. ITU-T K.126 (07/2017) NOTE 4 Wavesha
27、pes defined as maximum front time and minimum time to half value are expressed as T2. 3.1.5 differential-mode surge ITU-T K.95: Surge occurring between any two conductors or two groups of conductors at a given location. NOTE 1 The surge source may be floating, without a reference point or connected
28、to reference point, such as a chassis terminal, or a local earth/ground point. NOTE 2 Also known as metallic surge or transverse surge or symmetrical surge or normal surge. 3.1.6 electric screen b-IEC 60050-151: Screen of conductive material intended to reduce the penetration of an electric field in
29、to a given region. 3.1.7 impulse withstand voltage b-IEC/TR 60664-2-1: Highest peak value of impulse voltage of prescribed form and polarity which does not cause breakdown of insulation under specified conditions. 3.1.8 insulation coordination b-IEC/TR 60664-2-1: Mutual correlation of insulation cha
30、racteristics of electrical equipment taking into account the expected micro-environment and other influencing stresses. 3.1.9 insulation resistance b-IEC 62631-1: Resistance under specified conditions between two conductive bodies separated by the insulating material. 3.1.10 isolating transformer b-
31、IEC 60065: Transformer with protective separation between the input and output windings. 3.1.11 rated impulse voltage b-IEC/TR 60664-2-1: Impulse withstand voltage value assigned by the manufacturer to the equipment or to a part of it, characterizing the specified withstand capability of its insulat
32、ion against transient overvoltages. 3.1.12 rated winding d.c. ITU-T K.95: Maximum winding current that will not cause the winding conductor temperature to exceed a specified increase above the ambient temperature. 3.1.13 surge ITU-T K.95: Temporary disturbance on the conductors of an electrical serv
33、ice caused by an electrical event not related to the service. 3.1.14 virtual front time; T1: The front time T1 of a voltage impulse is 1/0.6 times the interval T between the instants when the impulse is 30% and 90% of the peak value b-IEC 60060-1. The front time T1 of a surge current impulse is 1.25
34、 times the interval T between the instants when the impulse is 10% and 90% of the peak value b-IEC 62475. NOTE Some standards use the 10% and 90% front time measurement for the voltage impulse. 3.1.15 virtual origin; O1: For the impulse voltage waveform, it is the instant at which a straight line dr
35、awn through the 30% and 90% amplitude values crosses the time axis b-IEC 60060-1. For the impulse current waveform, it is the instant at which a straight line drawn through the 10% and 90% amplitude values crosses the time axis b-IEC 60060-1. 3.1.16 virtual time to half-value; T2 b-IEC 60060-1b-IEC
36、62475: Interval of time between the instant of virtual origin O1 and the instant when the voltage or current has decreased to half the peak value. 3.1.17 withstand voltage b-IEC/TR 60664-2-1: Voltage to be applied to a specimen under prescribed test conditions which does not cause breakdown and/or f
37、lashover of a satisfactory specimen. 3.2 Terms defined in this Recommendation None. Rec. ITU-T K.126 (07/2017) 3 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: DMM Digital multimeter GDT Gas Discharge Tube IR Insulation Resistance LAN Local Area Netwo
38、rk LIT Lightning Isolation Transformer PoE Power over Ethernet POTS Plain Old Telephone System RJ45 Registered Jack 45 SPC Surge Protective Component SPD Surge Protective Device 5 Conventions This Recommendation uses the following: b-IEC 60617 Type 1 symbols to represent the different transformer co
39、nfigurations. Figure 5-1 shows the symbol for a two-winding transformer. Figure 5-1 Symbol for a two-winding transformer Figure 5-2 shows the symbol for a two-winding transformer with instantaneous voltage polarity indicators. Figure 5-2 Symbol for a two-winding transformer with polarity indication
40、Figure 5-3 shows the symbol for a two-winding transformer with an electric screen between the windings. 4 Rec. ITU-T K.126 (07/2017) Figure 5-3 Symbol for a two-winding transformer with electric screen Figure 5-4 shows the symbol for a transformer with centre-tapped windings. When testing is done wi
41、th shorted windings, the centre tap is also connected to that winding shorting link, other testing is done without any connection to the centre tap terminal. Figure 5-4 Transformer with centre-tapped windings 6 Component construction 6.1 Transformer basics The ideal transformer transforms the primar
42、y winding voltage, VP, to a secondary winding voltage of VS. The relationship is VS = VP/n, where n is the primary to secondary turns ratio. Similarly the primary winding current, IP, transforms to a secondary winding current of IS. The relationship is IS = IP*n. The transformer is 100 % efficient w
43、ith a primary power of VP*IP and a secondary power of VS*IS = (VP/n)*(IP*n) = VP*IP. The transformer winding inductance is considered to be high enough that it does not adversely affect the circuit operation. Figure 6-1 shows the ideal transformer. Figure 6-1 Ideal transformer 6.2 Transformer parasi
44、tics The primary winding and secondary winding will not be perfectly coupled and the non-coupled inductance is called leakage inductance. Circuit-wise winding leakage inductance can be emulated by adding a series inductor, LLP, to the primary winding and adding a series inductor, LLS, to the Rec. IT
45、U-T K.126 (07/2017) 5 secondary winding. (In circuit simulation, an alternative is to make the winding coupling factor, k, less than one.) Neither will the windings have zero resistance. Winding resistance is emulated by adding a series resistor, RP, to the primary winding and a series resistor, RS,
46、 to the secondary winding. The primary winding will not have infinite inductance and is represented by the inductor, LP, which transforms to a secondary inductor of LS = LP/n2. Inductor, LP, is effectively in parallel with the primary winding of the ideal transformer. Figure 6-2 shows the equivalent
47、 circuit with the parasitics. Example values are shown in Table 1. Figure 6-2 Ideal transformer with winding leakage inductance, winding resistance and the actual primary self-inductance added 6.3 Transformer core saturation Without a core, the primary and secondary windings have a low inductance an
48、d poor coupling. Figure 6-3 shows how the two windings are effectively independent. Current through a winding creates a widely dispersed magnetic flux, in and around the winding, see Figure 6-3. Figure 6-3 Transformer winding flux without a core in place When the windings are on a magnetic core, the
49、 flux is strongly constrained to the core resulting in a good coupling between the windings and a higher winding inductance value, see Figure 6-4. 6 Rec. ITU-T K.126 (07/2017) Figure 6-4 Transformer winding flux with a core in place The general magnetic formula for winding inductance is L = N*/IMAG, where N is the number of turns of the winding, is the winding flux and IMAG is the winding magnetizing current. The inductance L is proportional to the flux to current r
