1、STD-BSI BS EN b3000-2-7-ENGL L77b m Lb24bb7 0575308 b7L BRITISH STANDARD Electromagnetic compatibility Part 2. Environment Section 9. Description of HEMP environment - Radiated disturbance - Basic EMC publication The European Standard EN 61CW2-9 : 1996 has the status of a British Standard ICs 29.020
2、 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 1996 1996 61000-2-9 : EC 1000-2-9: STD-BSI BS EN bLOOO-2-9-ENGL Lb M Lb29bb 0575309 528 BS EN 61000-2-9 : 1996 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Rchn
3、icai Committee GEY210, Electromagnetic compatibiity, upon which the following bodies were represent - late-time HEMP (slow): - intermediate-time HEMP (medium); STD.BSI BS EN b1000-2-7-ENGL 177b Lb24bb7 0575115 621 Page 4 EN 61000-2-9 : 1996 Historically, most interest has been focused on the early-t
4、ime HEMP which was previously referred to as simply “HEMP“. Here we will use the term high-alutude EMF or “HEMP to include all three types. The tem NEMP1) covers many categories of nuclear EMPs including those produced by surface bursts (SREMP)21 or created un space systems (SGEMP)3). Because the HE
5、MP is produced by a high-alutude detonation, we do not observe other nuclear weapon environments such as gamma rays, heat and shock waves at the earths surface. HEMP was reported from highslutude U.S. nuclear tests in the South Pacific during the eariy 1960s, producing effects on electronic equipmen
6、t far from the burst location. 4 Definitions / GROUNDPLANE .* I presented in units of J/m*. STD-BSI BS EN b1000-2-7-ENGL 177b Lb24bb7 0575117 bT4 Page 6 EN 61000-2-9 : 1996 4.9 geomagnetic dip angle, 9dip: Dip angle of the geomagnetic flux density vector se, measured from the iocal horizontal in the
7、 magnetic north-south plane. dp = 90“ at the magnetic north pole, -90 at the magnetic south pole. NORTH EARTH I I I I I I I I SOUTH IEC 11m Figure 3 - Geomagnetic dip angle 4.10 ground zero: Point on the earths surface directly below the burst; sometimes called surface zero. 4.11 HEMP: Highaltitude
8、nuclear EMP. 4.12 highatude (nuclear explosion): Height of burst above 30 km altitude. 4.13 HOB: Height of burst. 4.14 Horizontal polarization: An electromagnetic wave is horizontally polarized if the magnetic field vector is in the incidence plane and the electric field vector is perpendicular to t
9、he incidence plane and thus parallel to the ground plane (figure 1). (This type of polarization is also called perpendicular or transverse electric (TE).) 4.15 incidence plane: Plane formed by the propagation vector and the normal to the ground plane. 4.16 low-altitude (nuclear explosion): Height of
10、 burst below 1 km altitude. STD-BSI BS EN bL000-2-7-ENGL L77b Lb2LibbS 0575LL 530 Page 7 EN 61000-2-9 : 1996 4.17 NEMP: Nuclear EMP; all types of EMP produced by a nuclear explosion. 4.18 polarization: Orientation of the electric field vector. 4.19 prompt radiation: Nuclear energy which leaves an ex
11、plosion within 1 1s. 4.20 SREYP: Source region EMP; the NEMP produced in any region where prompt radiation is also present producing currents (sources) in the air. 4.21 tangent point: Any point on the earths surface where a line drawn from the burst is tangent to the earai. 4.22 tangent radius: Dist
12、ance measured along the earths surface between ground zero and any tangent point. 4.23 vertical polarization: An electromagnetic wave is vettically polarized if the electric field vector is in the incidene plane and the magnetic field vector is perpendicular to the incidence plane and thus parallel
13、to the ground plane (figure 1). (This type of polarization is also called parallel or transverse magnetic (TM).) 5 Description of HEMP environment, radiated parameters 5.1 High-alatude bursts When a nuclear weapon detonates at high altitudes, the prompt radiation (x-rays, gamma rays and the air. The
14、se electrons are deflected in a coherent manner by the earths magnetic field. These transverse electron currents produce transverse electric fields which propagate down to the earths surface. This mechanism describes the generation of the early-time HEMP (figure 4) which is characterized by a large
15、peak electric field (tens of kilovolts per meter), a fast rise time (nanoseconds), a short pulse duration (up to about 100 ns) and a wave impedance of 377 Lz. The early-time HEMP exposes the earths surface within line-of-sight of the burst and is polarized transverse to the direction of propagation
16、and to the local geomagnetic field within the deposition region. In the northern and southem latitudes (.e. far from the equator) this means that the electric field is predominantly oriented horizontally (horizontal polarization). neutrons) deposit their energy in the dense air below the burst. In t
17、his deposition (source) region, the gamma rays of the nuclear exploeion produce Compton electrons by interactions with the molecules of * 1 STD.BSI BS EN b3000-2-9-ENGL 399b m Lb24bb9 0575337 477 Page 8 EN 61000-2-9 : 1996 Nudear explosion EM radiation Ground zero Figure 4 - Schematic representation
18、 of the early-time HEMP from a high-altitude burst Immediately following the initial fast HEMP transient, scattered gamma rays and inelastic gammas from weapon neutrons create adduonal ionization resulting in the second part (intermediate time) of the ., HEMP signal. This second signal is on the ord
19、er of 10 V/m to 100 Vlm and can occur in a time interval from 100 ns to tens of milliseconds. The last type of HEMP, late-time HEMP, also designated magnetohydrodynamic EMP (MHD-EMP) is generated from the same nudear burst. Late-time HEMP is characterized by a low amplitude electric field (tens of m
20、illivolts per meter), a slow rise time (seconds), and a long pulse duration (hundreds of seconds). These elds will cause similar induction currents in power lines and telephone networks as those associated with magnetic storms oten observed in Canada and the Nordic countries. Late-time HEMP can inte
21、ract with transmission and distribution lines to induce currents that result in hamnics and phase imbalances which can potenhlly damage major power system components (such as transformers). Page 9 EN 61000-2-9 1996 5.2 Spatial extent of HEMP on the earths surface The strength of the electric field o
22、bserved at the earths surface from a high-altitude explosion may vary significantly (in peak amplitude, rise time, duration and polarization) over the large area affected by the HEMP depending on burst height and yiekl (see figure 4). For example in the northern hemisphere, the maximum peak electric
23、 field identified as Emax occurs south of ground zero and can be as high as 50 kV/m, depending e.g. upon the height of burst and the weapon yield. Figure 5 shows the early-time HEMP tangent radius as a function of the height of burst (HOB). For an explosion at an altitude of 50 km, for example, the
24、affected area on the ground would have a radius of 800 km and for an altitude of 500 km, the tangent radius would be about 2 500 km. Figure 6 describes the variation of the peak HEMP fields over the exposed area of the earth. 5.3 HEMP time dependence In this subclause, electric field time waveforms
25、are suggested to represent the early-time, intermediate- time, and late-time HEMP environments. 5.3.1 Ea*-time HEMP waveform Examples of the variation of eariy-me HEMP waveforms are shown by the three waveforms A, B and C in figure 7 with the curves referenced to positions noted in figure 6. Since t
26、he incident waveshapes vary greatly and there is no way to predict the burst location, a generalized waveform is constructed for the HEMP that maintains the short rise time of the nearground-zero location and the large amplitude of the HEMP in the region of maximum peak amplitude. The envelope of al
27、l pulses, including the long fall time in the tangent region, would provide an extreme case. A more realistic waveform, constructed recommended in this section of IEC 1000-2 for civilian use. from the envelope of the Fourier transforms (frequency spectra) of all of them, is the 2,5/23 ns pulse _ STD
28、-BSI BS EN b1000-2-7-ENGL L77b 1bZVbb7 0575121 025 m Page 10 EN 61000-2-9 : 1996 for HOB s 500 km O 100 200 300 400 500 Height of burst HOB (km) Icc 1- Figure 5 - HEMP tangent radius as a function of height of burst (HOB) STD-BSI BS EN b1000-2-7-ENGL 177b 3bZYbbS 0575322 Tb3 Page 11 EN 61000-2-9 199
29、6 Magnetic North agnetic East Figure 6 -Typical variations in peak electric fields on the earths surface for burst altitudes between I00 km and 500 km and for ground zero between 30“ and 60 northern latitude. The data are applicable for yields of a few hundred kilotons or more. STD-BSI BS EN bL000-2
30、-7-ENGL L77b II Lb24bb7 0575323 7T8 Page 12 EN 61000-2-9 : 1996 E 3 w 50 40 50 20 10 0 -composL CUIw 2,m ns - MaXregiarr(8) - - Ground zero region (A) - Tangen regh (C) - O 20 40 60 80 100 Time (ns) IEC IZA6 Figure 7 - Different waveforms for three typical cases indicated in figure 6 (points A, B, C
31、) and the composite curve fit For these cases, the electric field early-time behaviour in free space of this wave is given by: whentsO (1) ol. k1 (e* -e -bt) when tO Eo, = 50 O00 V/m al =4x 107s-1 bl = 6 x lo8 sl ki = 1,3 where El is given in volts per metet; t is in seconds. A plot of equation (1)
32、is given in figures 8a and 8b. Figure 8a shows the pulse rise characteristics. The pulse decay behaviour is given in figure 8b. Because this waveform attempts to bound features of any early-time HEMP waveform, it is considered a standard waveform. The pulse has a peak amplitude of 50 kV/m, a 10 % to
33、 90 % rise time of 2,6 ns -41 ns = 2,5 ns, a time to peak of 4,8 ns, and a pulse width at haif maximum of 23 ns. The energy fluence of the early-time waveform is 0,114 Ji c denotes the velocity of light In this case, the criterion is satisfied for times less than 100 us. Therefore the waveforms show
34、n in figure 10 can be converted to magnetic fields by dividing the electric fields by (p is a phase shift (p= Oior 1 and e, q= 2xffor 6 and j). Figure 11 shows the ampliiude density spectrum of the high-altitude EMP electric field. Each of the components is shown separately. A E Frequency (Ht) IEC I
35、I&% Figure 11 - Amplitude spectrum of each HEMP component Page 19 EN 61000-2-9 : 1996 The power spectrum 8s) describes the energy density as a function of frequency (.e., for the far field criterion off io3 k): The energy fluence of the eariy-time ?1 waveform can be found by frequency domain giving:
36、 +a, w, = j S(f).df w, = j S(f).df 103 103 integrating equation (11) in the (12) Figure 12 shows the cumulative amount of energy uence of the early-time HEMP as a function of frequency. fl (Hz) IEC o9 12m Figure 12 - Fraction of energy fluence from f = IO3 Ht to f-1 Exmg& - The energy fluence below
37、IO5 Hz is 2 o/. Below 108 Hz it is about 98 %. Therefore 96 % is between 1 O5 Hz and 1 O* Hz. This example indicates that the important patt of the early-me HEMP pulse (from an energy fluence point of view) is in the 0,l MHz to 100 MHz frequency range. . ,. STD-BSI BS EN bL000-2-7-ENGL 377b 3b29bb7
38、0575333 T7q W Page 20 EN 61000-2-9 : 1996 As shown earlier in figure 11, the amplitude spectra for 2 and 3 are higher than 1 for frequencies below 104 Hz and 1 Hz, respectively. In spite of this situation, 2 and 3 have a total energy fluence of only 0,013 Jld while 1 alone has 0,114 JI&. The energy
39、fluence of the intermediate-time and late- time HEMP is negligible compared to the early-time HEMP. However, it shall be emphasized that the energy which is picked up from an electromagnetic field by an “antenna“ and then conducted to a “victim“ does not only depend upon the total incident energy fl
40、uence W$ of the field. This is because the voltages and currents that are induced at the electronics level in a system are also functions of the coupling mechanisms, the system topology, the impedance matching, and in power grids, the follow-on currents after a dielectric breakdown. 5.6 Weighting of
41、 the early, intermediate and late-the HEMP Intermediate-time and late-time HEMP effects are often neglected in the open literature, because on& their small amplitudes are considered. One might believe that 100 Vlm (intermediate-time) and 40 mV/m (lawtime) peak values may be neglected compared to the
42、 50 O00 Vlm of the early-time part. This is sometimes valid, especially if the “victim“ system (subsystem, equipment) is not too large in its physical dimensions (small coupling areas), e.g. mobile equipment such as vehicles. This limits the HEMP coupling to higher frequencies. However, often the me
43、chanism of coupling energy from a source (electromagnetic field) to a victim is frequency selective. General conclusions of importance shall not be made from the HEMP spectrum (figure 11) alone without considering the coupling mechanism. If a victim system is very large (such as electric Utity power
44、 systems or long telecommunication lines) or if a small installation is connected to these lines, it is important to consider the intermediate and the late-time signals of the high-altitude EMP. 5.7 ReffeCuOn and transmsson . Mien the HEMP wave (ea or intermediate-time HEMP portions only) impinges o
45、n the ground, part of the energy pulse is transmitted through the air-ground interface, whereas the remainder is reflected (see figure 13). I/ Renecled (scattered) wave Al R Refracted (transmied) wave IK 1- Figure i3 - Representation of incident, reflected and refracted waves - - STD-BSI BS EN bL000
46、-2-9-ENGL L79b 3b24bb9 0575332 900 = Page 21 EN 61000-2-9 : 1996 In almost all practical cases, the incident wave is altered by other structures in the vicinity of the potential victim. The field in the vicinity of power lines and buried communication cables, for example, is modified by the ground,
47、so that the field impressed on the cable is not the field of the incident wave but the total field. For the buried cable, the total field is the portion of the incident field that is transmitted into the soil, that is, the portion remaining after the reflection at the aidearth interface and absorpti
48、on in the soil. An above-ground collector, such as an overhead power line or a radio antenna tower, receives energy from both the direct and reflected pulses. Figures 14a and 14b show examples for the total horizontal electric field (incident plus reflected) for different heights above a highly cond
49、ucting surface and for a given height over different soil conductivities (see figure 1 for definition of angles). Figure 15 shows an exampie for different angles of elevation for a typical height and ground conductivity. Figures 16a and 16b show examples of the field transmitted into soil for different soil conductivities and for different depths. These examples clearly show the effect of the eatth on the incident electric field pulse. It is very important to consider the effects of reflect
