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 (08/2014) SERIES K: PROTECTION AGAINST INTERFERENCE Surge protective component application guide Gas discharge tubes Recommendation ITU-T K.99 Rec. ITU-T K.99 (08/2014) 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. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.99 2014-08-29 5 11.1002/1000/12289 Keywords Application circuits, electrical characteristics and ratings, gas discharge tube, GDT. _ * To access the Recom
4、mendation, 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 (08/2014) FOREWORD The International Telecommunication Union (ITU) is the United Nations spec
5、ialized 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 Recommendations on them
6、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. The approval of ITU-T R
7、ecommendations 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 “Administration“ is used fo
8、r 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 compliance with the Rec
9、ommendation 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 Recommendation is required of any
10、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 claimed Intellectual Property
11、 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 of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implem
12、enters 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 2014 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written
13、 permission of ITU. Rec. ITU-T K.99 (08/2014) 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 2 5 Construction 3 6 Electrical characteristics . 5 6.1 GDT spark-over voltage
14、 . 5 6.2 GDT glow voltage 7 6.3 GDT arc voltage . 7 6.4 GDT d.c. holdover voltage . 7 6.5 GDT capacitance 7 6.6 GDT oscillation 8 7 Electrical ratings . 9 7.1 GDT surge current capability . 9 7.2 AC discharge current test . 9 8 Application examples . 9 8.1 Two-electrode and three-electrode GDT compa
15、rison 9 8.2 Surge bonding . 10 8.3 GDT pass under protection for a.c. fault conditions 11 8.4 GDTs in a.c. mains applications . 11 8.5 Hybrid protectors 12 8.6 GDT thermal switch hybrid 13 8.7 GDT backup air gap (BUG) hybrid 14 8.8 Cascaded protection 15 8.9 Series connected GDTs for d.c. power appl
16、ications . 15 Bibliography. 18 Rec. ITU-T K.99 (08/2014) 1 Recommendation ITU-T K.99 Surge protective component application guide Gas discharge tubes 1 Scope This Recommendation in the surge protective component application guide series covers gas discharge tube technology. Gas discharge tubes (GDTs
17、) are switching type overvoltage protectors b-ITU-T K.96. Guidance is given for ITU-T K.12 compliant gas discharge tubes covering; construction, characteristics, ratings and application examples. 2 References The following ITU-T Recommendations and other references contain provisions which, through
18、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 revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the
19、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 this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.12 Rec
20、ommendation 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 the following terms defined elsewhere: 3.1.1 arc mode ITU-T K.12: The lowest impedance or on-state of a gas
21、 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-over“. 3.1.4 d.c. holdover voltage ITU-T K.12: The maximum d.c. voltage across the terminals of a gas discha
22、rge 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: The current that passes through a gas discharge tube when spark-over occurs. discharge current, alternating
23、: 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 the gas discharge tube. 3.1.6 discharge voltage ITU-T K.12: The voltage that appears across the terminals of
24、 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 pressure, designed to protect apparatus or personnel, or both, from high transient voltages. 2 Rec. ITU-T K.99 (0
25、8/2014) 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. 3.1.9 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-curr
26、ent 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 is flowing. It is sometimes called the glow-mode voltage. 3.1.11 glow-to-arc (transition) current ITU-T K.12:
27、 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 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
28、 “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: The voltage which causes spark-over when applied across the terminals of a gas discharge tube. spark-over v
29、oltage, 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 across the terminals of a gas discharge tube in the period between the application of an impulse of given wa
30、ve-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 connected from an accessible metal part to a nominal 125 V or 250 V line circuit within an appliance. NOTE This def
31、inition 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 This definition is based on the definition provided in b-UL 1414. 3.2.3 class Y2 component: Component connected
32、 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 within grounded equipment. NOTE This definition is based on the definition provided in b-UL 1414. 3.2.4 mod
33、es 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 flowing via other terminals. 3.2.5 surge protective component (SPC): Component specifically included in a d
34、evice 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 operation. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AWG Am
35、erican Wire Gauge Rec. ITU-T K.99 (08/2014) 3 BUG Backup air Gap GDT Gas Discharge Tube HF High Frequency IC Integrated Circuit MOV Metal-Oxide Varistor POTS Plain Old Telephone Service PTC Positive Temperature Coefficient SPC Surge Protective Component SPD Surge Protective Device xDSL x-type Digita
36、l Subscriber Line 5 Construction Gas discharge tubes consist of two or more metal electrodes separated by a small gap and hermetically sealed to a ceramic or glass cylinder, Figure 1 shows a two-electrode GDT. Figure 1 “See-through“ view of a surface mount two-electrode GDT The cylinder is filled wi
37、th a noble gas mixture. When sufficient voltage is applied to the electrodes, gas ionization is caused and spark-over occurs into a glow discharge 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 dete
38、rmined primarily by the electrode spacing, gas pressure and gas mixture, the turn-on process initiates at the spark-over (breakdown) voltage. Once spark-over occurs, various operating states are possible, depending upon the external circuitry. These states are shown in Figure 2. At currents less tha
39、n the glow-to-arc transition current, a glow region exists. At low currents in the glow region, the voltage is nearly 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 t
40、han the glow-to-arc transition. The GDT electrical characteristic, in conjunction with the external circuitry, determines the ability of the gas tube to extinguish after passage of a surge, and also determines the energy dissipated during the surge. 4 Rec. ITU-T K.99 (08/2014) If the applied voltage
41、 (e.g., transient) rises rapidly, the time taken for the ionization/arc formation process may allow the transient voltage to exceed the value 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
42、-rise of the applied voltage (transient). Figure 2 Typical GDT voltampere characteristic A single chamber three-electrode GDT has two cavities separated 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
43、 other cavity, even though the other cavity voltage may be below its spark-over voltage; see Figure 7. Figure 3 “See-through“ view of a leaded three-electrode GDT Rec. ITU-T K.99 (08/2014) 5 Because of their switching action and rugged construction, gas tubes exceed other voltage limiting surge prot
44、ective components in current-carrying capability. Many telecommunications gas tubes can easily carry surge currents as high as 20 kA, 8/20, depending 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, gen
45、erally less than 2 pF. This allows their use in many high-frequency circuit applications. When gas discharge tubes (GDTs) operate, they may generate high-frequency radiation, which can influence sensitive electronics. It is therefore wise to place GDT circuits at a certain distance from the electron
46、ics. 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-
47、over voltage, impulse spark-over voltage, arc voltage and d.c. holdover voltage. 6.1 GDT spark-over voltage The GDT spark-over voltage depends on the rate at which the voltage is applied. 6.1.1 d.c. and impulse spark-over voltage The maximum value of limited voltage depends on the surge voltage rate
48、 of rise. Figure 4 shows a typical relationship between the GDT d.c. spark-over and the impulse, fast rate of voltage rise, spark-over of a GDT. In this example, the minimum 1000 V/s spark-over voltage of 575 V occurs with a 150 V d.c. spark-over voltage GDT. The much lower voltage 75 V d.c. spark-o
49、ver GDT has a 1000 V/s spark-over voltage of 700 V nine times higher than the d.c. value. Where fast rising transients occur, often the 150 V GDT will be more effective than a 75 V GDT, due to the gas mixture that is used to achieve a low voltage GDT. Figure 4 Fast dv/dt spark-over voltage variation with d.c. spark-over voltage 6 Rec. ITU-T K.99 (08/2014) Figure 4 shows absolute values of voltage. In terms of relative voltage increase, this factor continuously decreases with
