1、 ETSI TR 100 283 V2.2.1 (2007-08)Technical Report Environmental Engineering (EE);Transient voltages at Interface “A“on telecommunicationsdirect current (dc) power distributionsETSI ETSI TR 100 283 V2.2.1 (2007-08) 2 Reference RTR/EE-020132 Keywords power supply, protection, transient ETSI 650 Route
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6、ight and the foregoing restriction extend to reproduction in all media. European Telecommunications Standards Institute 2007. All rights reserved. DECTTM, PLUGTESTSTM and UMTSTM are Trade Marks of ETSI registered for the benefit of its Members. TIPHONTMand the TIPHON logo are Trade Marks currently b
7、eing registered by ETSI for the benefit of its Members. 3GPPTM is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 3 Contents Intellectual Property Rights4 Foreword.4 1 Scope 5 2 References 5 3 Definitions,
8、symbols and abbreviations .5 3.1 Definitions5 3.2 Symbols5 3.3 Abbreviations .6 4 Void6 5 Typical power distribution .6 6 Characteristics of a power fault transient .7 7 The transient, part 17 8 Analysis of part 1 .8 8.1 Increasing distribution resistance .9 8.2 Decreasing the fault clearance time9
9、8.3 Decreasing power distribution inductance .10 8.3.1 Calculating inductance10 8.3.2 Measuring inductance .11 8.4 Summary 11 8.5 Recommendations 11 9 The transient, part 211 10 Analysis of part 2 .12 10.1 Absorbing the energy .12 10.2 Dissipating the energy13 10.3 Recommendations 13 11 Testing for
10、immunity to transients .14 11.1 Transient immunity test circuit; by applying real power distribution to an installation model (high power systems)14 11.2 Transient immunity test circuit; by analogue circuit simulation 15 12 Conclusion16 History 17 ETSI ETSI TR 100 283 V2.2.1 (2007-08) 4 Intellectual
11、 Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: “Intellectual Property Rights (IPR
12、s); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards“, which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (http:/webapp.etsi.org/IPR/home.asp). Pursuant to the ETSI IPR Policy, no investigation, including IPR searc
13、hes, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This Technical Report (TR) has been produced by ET
14、SI Technical Committee Environmental Engineering (EE). ETSI ETSI TR 100 283 V2.2.1 (2007-08) 5 1 Scope Short duration transient disturbances can occur on dc power distributions when a short circuit fault occurs in part of that distribution. The energy contained in the transient can be sufficient to
15、do considerable damage to equipment connected to the distribution unless measures are taken to suppress or absorb this energy. The present document examines the parameters of dc power distributions within the scope of EN 300 132-2 1 that significantly contribute to the energy contained by a transien
16、t, discusses ways in which the transient can be controlled to reduce its harmful effects, and suggests ways in which the immunity of an electronic unit or a substantial telecommunications installation might be tested. 2 References For the purposes of this Technical Report (TR), the following referen
17、ces apply: NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. 1 ETSI EN 300 132-2: “Environmental Engineering (EE); Power supply interface at the input to telecommunications equipment; Part 2: Operated by direct cu
18、rrent (dc)“. 3 Definitions, symbols and abbreviations 3.1 Definitions For the purposes of the present document, the following terms and definitions apply: fault: short circuit of the negative conductors of the power distribution to any earthed part of an equipment or installation interface “A“: The
19、definition given in EN 300 132-2 1 applies. 3.2 Symbols For the purposes of the present document, the following symbols apply: A Ampere C Capacitance d separation of conductors dc direct current E Energy I currentL inductance l length of conductor n number of ways current is split r diameter of cond
20、uctor R Resistance t time U voltage (nominal voltage) V voltage (overvoltage) magnetic permeability of insulation separating conductors ETSI ETSI TR 100 283 V2.2.1 (2007-08) 6 3.3 Abbreviations For the purposes of the present document, the following abbreviations apply: EUT Equipment Under Test PDF
21、Power Distribution Frame UBBattery voltage 4 Void 5 Typical power distribution Virtually all equipment operated in telecommunications centres has a battery as a backup source of power in the event of a mains failure. Batteries store very large amounts of energy and under fault conditions are able to
22、 deliver very large currents for short periods far in excess of the ratings of fuses or circuit breakers in the path of the fault. Figure 1 shows a typical power distribution (negative conductors only) in a large installation. The current supplied from the power plant and battery is broken down into
23、 several lower current feeds at each Power Distribution Frame (PDF). The power cables are sized according to the current they have to carry and the voltage drop that can be tolerated, and are protected by suitably rated fuses or breakers in each PDF. In large installations the conductors close to th
24、e battery may be copper or aluminium bus bars. The positive return conductors will be parallel with the negative conductors but will not include current protection devices. Figure 1: Typical power distribution ETSI ETSI TR 100 283 V2.2.1 (2007-08) 7 6 Characteristics of a power fault transient least
25、affectedfeedsmostaffectedfeedsMAINPDF SECONDARYPDFRACKFUSEPANELcablecablebus-barFigure 2: Power fault applied in an equipment rack Figure 2 shows the fault current path when a fault occurs in a branch of the power distribution. The voltage transient experienced by the branches of the distribution no
26、t associated with the fault can be divided into two distinct parts and are shown in figures 4 and 5: - Part 1: begins at the moment the fault is applied (t0) and ends at the instant the protection device clears (t1); - Part 2: begins at the instant the protection device clears the fault (t1), and en
27、ds (t2) when the voltage returns to its value before the fault was applied. 7 The transient, part 1 When the fault is applied the current rises rapidly at an exponential rate: I=UR(1- e )RLtB(1) Where: UB= the battery voltage in float mode. R = the sum of the resistances in the fault circuit which i
28、nclude: - (a) fault resistance itself; - (b) total conductor resistance in both negative and return legs; - (c) the resistance of fuses or breakers; - (d) the internal resistance of the battery. L = the inductance of the fault circuit loop. t = the time elapsed from the fault being applied. ETSI ETS
29、I TR 100 283 V2.2.1 (2007-08) 8 It can be seen that if inductance is ignored, the potential fault current can be extremely high. I=URB(2) Currents of in excess of 1 kA are not unusual, depending on where the fault occurs in the distribution. In practice the inductance of the fault circuit cannot be
30、ignored and it plays an important role in the behaviour of the power distribution as will be seen next. 8 Analysis of part 1 Two things are of concern during this part of the fault transient: a) the magnitude of the fault current; b) the voltage at the input of all other equipment sharing the same p
31、ower distribution. The magnitude of the fault current largely determines the amount of energy that will be dissipated after the fault is cleared by the protection device. E = 1/2 LI2 (3) Where: - E is the energy (joules); - L is the inductance of the fault circuit (henrys); - I is the fault current
32、at the instant the fault is cleared by the protection device (amps). The voltage at the input of all other equipment sharing the same distribution falls to below the normal, minimum steady state value for some portion of the clearing time of the protection devices, requiring the dc/dc converters to
33、store charge on “hold up“ capacitors to ride through this fall in supply voltage. The magnitude and duration of the fall depends on many parameters of the power distribution already mentioned e.g. R, t1and L. How these can be controlled is explained in clauses 8.1, 8.2 and 8.3. The general objective
34、 is to reduce the energy stored in the distribution inductance which from equation 1 means that the distribution inductance itself (L) must be kept to a minimum and the peak fault current (I) must be controlled by resistance in the distribution (R) or by the use of very short clearance time fuses (t
35、1). ETSI ETSI TR 100 283 V2.2.1 (2007-08) 9 8.1 Increasing distribution resistance Resistance would seem to be an undesirable feature to have in a power distribution but used in the right way, there are advantages worth having by its inclusion that more than compensate for the power losses. Figure 3
36、: A controlled resistive power distribution Figure 3 shows a power distribution where the resistance has been concentrated in the most remote branches. The fault current is limited to: I = U(n + 1)RB(4) But the voltage supplied to the other rack power feeds can be reasonably expected to remain above
37、: U = nU1+nB(5) after the influence of inductance in the circuit has passed. If dc/dc converters are designed to operate at U volts, only the drop in voltage due to circuit inductance needs to be covered by “hold up“ capacitors in the converters. Such a resistive power distribution permits the use o
38、f circuit breakers, with their longer clearance times compared to fuses, and at the same time, there is no need to increase the hold up time of the power converters to match the clearance time of breakers. 8.2 Decreasing the fault clearance time The response of fuses and circuit breakers to fault cu
39、rrents needs to be understood. A fuse needs time to break an excessive current i.e. a current greater than its rated value. The larger the excess current the sooner the fuse element reaches its melting point and ruptures. However, even with very high levels of excess current, a fuse will still have
40、a finite clearance time. Depending on the design of the fuse and the excess current level, clearance times can vary from 1 ms to more than 10 ms. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 10Circuit breakers have a rather different response to large fault currents. The time needed to clear an excessive c
41、urrent is mainly dependent on the inertia of the moving mass of the breaker mechanism and contacts. The range of clearance times for breakers is usually longer than for fuses, the fastest being 4 ms to 6 ms and the longest extending beyond 15 ms. UBFigure 4: Voltage transient waveform Figure 5: Curr
42、ent transient waveform The importance that these overcurrent protection devices play can be seen in the diagrams of figures 4 and 5 when coupled to the inductance present in the fault circuit. The fault current rises exponentially towards the maximum level already established in equation (2) above,
43、and, depending on the clearance time of the protection device (tx or t1in figures 4 and 5, battery in float mode UB) being used, the peak fault current may be limited by the inductance of the fault loop. If the clearance time is long, then the peak current is limited only by the resistance of the fa
44、ult loop. 8.3 Decreasing power distribution inductance 8.3.1 Calculating inductance The inductance of any fault circuit is reduced when all the negative conductors are closely coupled to the earth return conductors, the closer the coupling the less inductance there is. Negative and return conductors
45、 made as a bonded pair (e.g. twin cables) provide a good solution with consistent performance figures for inductance per metre length. If this is not possible, then separate conductors run side by side as closely as possible gives good results, or negative conductors tied at frequent intervals to a
46、positive return bus-bar also reduces distribution inductance. The theoretical equation for the inductance (L) of a pair of parallel conductors is shown below: rdlnl =L(6) Where: - r = the radius of the conductors; - d = the separation of the conductor centres; - = the magnetic permeability of the in
47、sulation that separates the conductors; - l = the length of conductor. ETSI ETSI TR 100 283 V2.2.1 (2007-08) 11This equation is only approximately correct as it assumes that “d“ is much greater than “r“ which is not true of a pair of power conductors. 8.3.2 Measuring inductance A more accurate metho
48、d of characterizing the inductance of a conductor pair is by direct measurement. This can be done using a representative length of bonded pair cable, shorting the two conductors at one end and measuring the inductance at the other end. As the low frequency inductance is the parameter that stores ene
49、rgy when fault currents flow in the cables, the measuring frequency should be the minimum that permits a dependable reading from the measuring instrument. Higher measuring frequencies will give erroneous readings due to distributed cable capacitance between conductors and from each conductor to its surroundings. Measurements can also be made on an installation during construction or before power is connected. 8.4 Summary Figure 4 shows a typical transient caused by a fault, as seen at the input to a branch sharing the same secondary PDF, or the same rack fu
