Lightning current

Waveforms of a lightning current, (a) Lump, (b) Double exponent, (c) CIGRE. 

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A significant characteristic for lightning protection is the rate of rise of the current waveform. It has been generally assumed in the recent past that the lightning current waveform reaches a peak in some 1 to 3 j sec. More recent information by... 

Danger facilities of large dimensions requiring the best possible protection should be provided with a system of catenaries suspended from tall masts. These catenary wires must pass to ground some distance away from the protected structure so that the lightning current may go to ground at a distant point. 

For the purpose of a numerical estimate, we may assume an intense lightning current of crest value i = 100 k amp and a ground resistance of R= lOQ. The inductance of a single vertical conductor is about 160 j H per 100 m and the rate of rise of the front of the lightning, as reported by Llewellyn (J ), may be taken as 50k amp/ /4 u sec. If the height of the chimney above ground is 10 m, the top of the lightning conductor is raised to a potential with respect to true earth which amounts to ... 

There is one more mechanical force worth considering. If a lightning conductor follows a right-angle bend on a building and this conductor has to discharge a lightning current, it will be... 

Indirect effects of lightning can cause power transients and anomalies that can damage sensitive/criti-cal LRUs or damage wire looms. EMI can be induced into wiring by the lightning currents flowing on the outside of the fuselage. 

Identification of effects of lightning current causing possible damage... 

Thermal effects linked with lightning current are due to the resistive heating caused by the circulation of an electric current flowing through the resistance of a conductor as a metallic storage tank. Thermal effects are also relevant to the heat generated in the root of the arcs at the attachment point and in all the isolated parts involved in arc development (e.g. spark gaps). 

Guidance is given in the European Standard Protection against Lightning" EN 62305-1 (2006) in order to evaluate the temperature rise of conductors subjected to the flow of a lightning current. 

The 3-D transient temperature distribution in metals struck by different lightning currents is determined using a computer program based on the volume technique, developed in MetwaUy et al. 2003. The temperature field within the material 0(r, z, i) is obtained upon solving the energy equation subjected to the appropriate boimdary and initial conditions. The results are presented in MetwaUy et al. 2003. 

Field changes Discrete temporal jumps in the electric field of thunderstorms coincident with lightning strokes or flashes, caused by the neutralization of charges due to lightning currents. 

Takami J, Okabe S. Observational results of lightning current on transmission towers. IEEE Trans. Power Del. 2007 22(l) 547-56. 

Lightning protection Based on minimum and maximum lightning current parameter for... 

D 2 Physical damage (fire/explosion, chemical, etc.) due to lightning current effect including spark... 

Measured results of lightning current amplitudes. (From IEEE Guide for Improving the Lightning Performance of Transmission Lines. 1997 Ametani, A. et al. 2002. lEE Japan WG Report. Technical Report No. 872 CRIPEI WG. 2003. Guide to transmission line protection against lightning. Report T72 Ametani, A. and T. Kawamura. 2005. IEEE Trans. Power Deliv. 20 (2) 867-875 Anderson, R. B. and A. J. Eriksson. 1980. Electro 69 65.)... 

System Voltage (kV) Lightning Current (kA) Tower Height/Geometry (m) Surge Impedance (i3) Footing Resistance... 

The parameters were the same as those in Table 2.4 for a 77-kV system, except for a lightning current of 40 kA based on the field measurement [33]. The lower phase arc horn voltage was relatively smaller than those of the other phases on the 500-kV (EHV) line compared with those on the 77-kV line. Thus, an arc horn flashover phase on an EHV line is independent of the AC source voltage, and the lower phase flashover is less probable than those of the other phases. On the contrary, flashover probability is the same on each phase, and a flashover is dependent on the AC source voltage on a low voltage line. 

Lightning strikes a tower or a GW in most cases. Occasionally it strikes a PW when the lightning current is small [37]. In field measurements of lightning strikes on a 1100 kV transmission system, it was found that lightning strikes a PW when the current is less than 35 kA[25]. 

This analysis is based on a step function current. In reality, the lightning current has a much slower rise time at the wave front, and thus the lightning overvoltage becomes much lower. Such an analysis can be carried out considering the wave front, but a hand calculation of this would be quite tedious. 

Lightning to the tower nearest to the substation A lightning current flowed into a ground mesh and induced a surge voltage in a control cable. A differential mode voltage was induced in the diode. 

FIGURE 6.9 A disturbed circuit for Case No. 1 (a) disturbed circuit, (b) flow of the surge voltage, and (c) countermeasures. Table 6.8 Recommended Values of Lightning Currents Flowing into a Ground Mesh... 

Assuming that a lightning current of 30 kA strikes a tower of a 66-kV system, the current flowing into the mesh is estimated as shown in Table 6.8. 

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