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.99 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2017) SERIES K: PROTECTION AGAINST INTERFERENCE Surge protective component application guide Gas discharge tubes Recommendation ITU-T K.99 Rec. ITU-T K.99 (07/2017) i
2、 Recommendation ITU-T K.99 Surge protective component application guide Gas discharge tubes Summary Recommendation ITU-T K.99 describes the construction, characteristics, ratings and application examples of gas discharge tubes (GDTs) intended for the protection of exchange and outdoor equipment, sub
3、scriber or customer equipment and telecommunication lines from surges. Version 2.0 of this Recommendation has added four informative appendices: 1) Appendix I: Durability test using “Fast“ GDTs; 2) Appendix II: Spark-over dark effect; 3) Appendix III: GDT component form factors; 4) Appendix IV: Thre
4、e-electrode GDT operation in Ethernet circuits. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.99 2014-08-29 5 11.1002/1000/12289 2.0 ITU-T K.99 2017-07-29 5 11.1002/1000/13277 Keywords Application circuits, electrical characteristics and ratings, gas discharge tube, GDT.
5、 _ * 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-en. ii Rec. ITU-T K.99 (07/2017) FOREWORD The International Telecommunication Union (ITU) is
6、 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 ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing
7、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 turn, produce Recommendations on these topics.
8、 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 In this Recommendation, the expression “Ad
9、ministration“ 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.g., interoperability or applicability) and
10、 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 suggest that compliance with the Recommenda
11、tion 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 Property Right. ITU takes no position concerning the evidence, validity or applicability of claim
12、ed 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 received notice of intellectual property, protected by patents, which may be required to implement this Recommendat
13、ion. 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 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, witho
14、ut the prior written permission of ITU. Rec. ITU-T K.99 (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 Recommendation . 2 4 Abbreviations and acronyms 3 5 Construction 3 6 Electrical characteristics . 5 6.1 GD
15、T spark-over voltage . 5 6.2 GDT glow voltage 7 6.3 GDT arc voltage . 8 6.4 GDT d.c. holdover voltage . 8 6.5 GDT capacitance 8 6.6 GDT oscillation 8 7 Electrical ratings . 9 7.1 GDT surge current capability . 9 7.2 a.c. discharge current test . 9 8 Application examples . 10 8.1 Two-electrode and th
16、ree-electrode GDT comparison 10 8.2 Surge bonding . 11 8.3 GDT pass under protection for a.c. fault conditions 11 8.4 GDTs in a.c. mains applications . 12 8.5 Hybrid protectors 12 8.6 GDT thermal switch hybrid 14 8.7 GDT backup air gap hybrid 14 8.8 Cascaded protection 15 8.9 Series connected GDTs f
17、or d.c. power applications . 16 Appendix I Durability test using “Fast“ GDTs . 18 I.1 Testing 18 Appendix II Spark-over dark effect 20 II.1 Testing 20 Appendix III GDT component form factors . 22 III.1 Introduction 22 III.2 Outlines of GDTs with different form factors 22 III.3 Outline of GDTs with c
18、oaxial form factors 26 III.4 Outlines of GDTs with reduced axial length and two-electrodes . 26 III.5 Outlines of GDTs with reduced axial length and three-electrodes . 28 iv Rec. ITU-T K.99 (07/2017) Page III.6 General . 29 Appendix IV Three-electrode GDT operation in Ethernet circuits . 30 IV.1 Int
19、roduction 30 IV.2 Three-electrode GDT applied to Ethernet twisted pair 30 IV.3 Three-electrode GDT applied to Ethernet powering pair . 33 Bibliography. 34 Rec. ITU-T K.99 (07/2017) 1 Recommendation ITU-T K.99 Surge protective component application guide Gas discharge tubes 1 Scope This Recommendatio
20、n in the surge protective component application guide series covers gas discharge tube (GDT) technology. Gas discharge tubes are switching type overvoltage protectors b-ITU-T K.96. Guidance is given for ITU-T K.12 compliant GDTs covering; construction, characteristics, ratings and application exampl
21、es. 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 Recommendations and other references are subject to rev
22、ision; 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 regularly published. The reference to a document within thi
23、s Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.12 Recommendation ITU-T K.12 (2010), Characteristics of gas discharge tubes for the protection of telecommunications installations. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses
24、 the following terms defined elsewhere: 3.1.1 arc mode ITU-T K.12: The lowest impedance or on-state of a gas discharge tube during normal operation. 3.1.2 arc voltage ITU-T K.12: The voltage measured across the tube while in lowest impedance state or arc mode. 3.1.3 breakdown ITU-T K.12: See “spark-
25、over“. 3.1.4 d.c. holdover voltage ITU-T K.12: The maximum d.c. voltage across the terminals of a gas discharge tube under which it may be expected to clear and to return to the high impedance state after the passage of a surge, under specified circuit conditions. 3.1.5 discharge current ITU-T K.12:
26、 The current that passes through a gas discharge tube when spark-over occurs. discharge current, alternating: The r.m.s. value of an approximately sinusoidal alternating current passing through the gas discharge tube. discharge current, impulse: The peak value of the impulse current passing through
27、the gas discharge tube. 3.1.6 discharge voltage ITU-T K.12: The voltage that appears across the terminals of a gas discharge tube during the passage of discharge current. 3.1.7 gas discharge tube ITU-T K.12: A gap, or several gaps, in an enclosed discharge medium, other than air at atmospheric press
28、ure, designed to protect apparatus or personnel, or both, from high transient voltages. 2 Rec. ITU-T K.99 (07/2017) 3.1.8 glow current ITU-T K.12: The current which flows after spark-over when circuit impedance limits the discharge current to a value less than the glow-to-arc transition current. 3.1
29、.9 glow mode ITU-T K.12: This is a semi on-state in the area of the V/I curve where only a limited glow-current flows and the device has not yet turned on or reached the lowest impedance arc-mode. 3.1.10 glow voltage ITU-T K.12: The peak value of the voltage drop across the GDT when a glow current i
30、s flowing. It is sometimes called the glow-mode voltage. 3.1.11 glow-to-arc (transition) current ITU-T K.12: The current required for the gas discharge tube to pass from the glow-mode into the arc mode. 3.1.12 impulse waveshape ITU-T K.12: An impulse waveform designated as x/y has a rise time of x s
31、 and a decay time to half value of y s as standardized in IEC 60060. 3.1.13 residual voltage ITU-T K.12: See “discharge voltage“. 3.1.14 spark-over ITU-T K.12: An electrical breakdown of the discharge gap of a gas discharge tube. Also referred to as “breakdown“. 3.1.15 spark-over voltage ITU-T K.12:
32、 The voltage which causes spark-over when applied across the terminals of a gas discharge tube. spark-over voltage, d.c.: The voltage at which the gas discharge tube sparks over when a slowly rising d.c. voltage up to 2 kV/s is applied. spark-over voltage, impulse: The highest voltage which appears
33、across the terminals of a gas discharge tube in the period between the application of an impulse of given wave-shape and the time when current begins to flow. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 antenna-coupling component: Component connect
34、ed from an accessible metal part to a nominal 125 V or 250 V line circuit within an appliance. NOTE This definition is based on the definition provided in b-UL 1414. 3.2.2 class Y1 component: Component connected from an accessible metal part to a nominal 250 V line circuit within equipment. NOTE Thi
35、s definition is based on the definition provided in b-UL 1414. 3.2.3 class Y2 component: Component connected from an accessible metal part to a nominal 125 V line circuit within double insulated equipment, or a component that is connected from an accessible metal part to a nominal 250 V line circuit
36、 within grounded equipment. NOTE This definition is based on the definition provided in b-UL 1414. 3.2.4 modes of protection (of a voltage limiting surge protective device (SPD) or equipment port): List of terminal-pairs where the diverted surge current is directly between that terminal-pair without
37、 flowing via other terminals. 3.2.5 surge protective component (SPC): Component specifically included in a device or equipment as part of the mitigation of onward propagation of overvoltages or overcurrents or both. NOTE The selected component should not significantly degrade the normal system opera
38、tion. Rec. ITU-T K.99 (07/2017) 3 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AWG American Wire Gauge BUG Backup air Gap GDT Gas Discharge Tube HF High Frequency IC Integrated Circuit MOV Metal-Oxide Varistor PoE Power over Ethernet POTS Plain Old
39、Telephone Service PTC Positive Temperature Coefficient SMT Surface Mount Technology SPC Surge Protective Component SPD Surge Protective Device xDSL x-type Digital Subscriber Line 5 Construction Gas discharge tubes consist of two or more metal electrodes separated by a small gap and hermetically seal
40、ed to a ceramic or glass cylinder, Figure 1 shows a 2-electrode GDT. Figure 1 “See-through“ view of a surface mount two-electrode GDT The cylinder is filled with a noble gas mixture. When sufficient voltage is applied to the electrodes, gas ionization is caused and spark-over occurs into a glow disc
41、harge mode and finally a low-voltage arc condition when sufficient surge current is available. When a slowly rising voltage across the gap reaches a value determined primarily by the electrode spacing, gas pressure and gas mixture, the turn-on process initiates at the spark-over (breakdown) voltage.
42、 Once spark-over occurs, various operating states are possible, depending upon the external circuitry. These states are shown in Figure 2. At currents less than the glow-to-arc transition current, a glow region exists. At low currents in the glow 4 Rec. ITU-T K.99 (07/2017) region, the voltage is ne
43、arly constant. Beyond this abnormal glow region the tube impedance decreases in the transition region into the low-voltage arc condition. The arc-to-glow transition current may be lower than the glow-to-arc transition. The GDT electrical characteristic, in conjunction with the external circuitry, de
44、termines the ability of the gas tube to extinguish after passage of a surge, and also determines the energy dissipated during the surge. If the applied voltage (e.g., transient) rises rapidly, the time taken for the ionization/arc formation process may allow the transient voltage to exceed the value
45、 required for breakdown in the previous paragraph. This voltage is defined as the impulse breakdown voltage and is generally a positive function of the rate-of-rise of the applied voltage (transient). Figure 2 Typical GDT voltampere characteristic A single chamber 3-electrode GDT has two cavities se
46、parated by a centre ring electrode; see Figure 3. The hole in the centre electrode allows gas plasma from a conducting cavity to initiate conduction in the other cavity, even though the other cavity voltage may be below its spark-over voltage; see Figure 7. Rec. ITU-T K.99 (07/2017) 5 Figure 3 “See-
47、through“ view of a leaded three-electrode GDT Because of their switching action and rugged construction, gas tubes exceed other voltage limiting surge protective components in current-carrying capability. Many telecommunications gas tubes can easily carry surge currents as high as 20 kA, 8/20, depen
48、ding on design and size values currents of 100 kA can be achieved. The construction of gas discharge tubes is such that they have very low capacitance, generally less than 2 pF. This allows their use in many high-frequency circuit applications. When gas discharge tubes operate, they may generate hig
49、h-frequency radiation, which can influence sensitive electronics. It is therefore wise to place GDT circuits at a certain distance from the electronics. The distance depends on the sensitivity of the electronics and how well the electronics are shielded. Another method to avoid the effect is to place the GDT in a shielded enclosure. 6 Electrical characteristics In terms of voltage limiting performance, a GDT has four key parameters; d.c. spark-over voltage, impulse
