This part describes protection from the induced effects of lightning, including the protection system by SPD Types 2 and 3cable shielding, isc for installation of SPD, etc. The standard is now in your shopping cart. Withdrawn Buy this standard. Iec download Protection against electric shocks and electrical fires. Views Page Talk View source History. A list of my favorite links model child care health policies pdf le repertoire de la cuisine pdf steam turbines lecture notes pdf khawateen digest september pdf download lei organica do municipio de iranduba pdf lightning protection systems pdf prywatyzacja w polsce pdf mathematica book stephen wolfram pdf asking for directions exercises pdf commonly used english words with tamil meaning pdf mdu result b tech pdf file history of prophet muhammad in tamil pdf nortel t user guide pdf cheikh ferkous pdf kec subir un pdf a internet gratis vi editor tutorials pdf cadillac sedan ief owners manual pdf asp net mvc 4 itextsharp html to pdf morfologi kapang pdf bhakti rasamrta sindhu pdf.
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For example, will making a grounding rod longer or a grounding system bigger always reduce the risk of lightning damage? Reality may be different from expectations. One way to set expectations is to study the effect of a ground rod on the waveshape of a surge, which can tell us a lot about how the ground rod is behaving.
Standards have advice on this. For example, based on a reading of the IEC  standard, we might assume that the waveshapes of the current flowing in the grounding system and that flowing in the electrical circuit are the same — implying that the grounding system is simply a resistance. But is that really the case? Lightning Measurements at Structures For another view, consider the work of Rakov, Uman and their associates at the Camp Blanding triggered lightning facility in Florida.
They have a facility with a launch tower [for rocket-induced lightning] and an instrumented building. They have shown  that the waveshapes of the currents in the grounding system and those entering the building electrical circuits are considerably different [in their case for a subsequent surge]; and they attribute the difference to the performance of the ground rods in the two cases.
That observation suggests that we need to look more closely at the effects of ground rods on an incident lightning waveform. Maybe ground rods can act differently than the IEC expects. From the recorded waveforms of the currents at the launch tower and at the ground rods, Rakov et al found that the surge currents in the ground rods have a much faster rise time and a much shorter duration than those of the incident surge.
The short explanation is that the ground rods used in the study by Rakov et al  are acting like lossy capacitors — probably not what most of us would expect. Generally, ground rods have been assumed to behave like resistors. The unexpected behavior occurs because ground rods also have reactive elements. The effect of these reactive elements on the wave shape of a surge will be greatest on high frequency components of the surge.
The high frequency components of the surge primarily affect the surge rise-time, so the reactive elements of a ground rod may change the rise-time of the surge. The fall-time is generally less affected, depending on the type of surge and the resistance of the ground rod. To assess their impact on lightening, quite a bit of work has been done recently on the high-frequency behavior of ground rods . The results can be divided into two categories: short ground rods which look capacitive, and long ground rods which look inductive .
Short Ground Rods Short ground rods are most likely to be found at residences. A number of groups  have estimated the capacitance of short ground rods, with estimates running around 3. The ground rod capacity is in parallel with the resistance of the ground, so the effect of the capacity depends in the resistivity of the soil.
A typical short ground rod is 2 m long. This ground rod in low resistivity 50 ohm-m and high resistivity ohm-m soil would have a resistance of about 25 ohms and ohms, respectively. Using these resistances and a capacitance of 3. This figure shows that a ground rod in low resistivity soil is characterized by a modest slowing of the rise time of the surge.
The curve for the ohm-m soil has a much greater slowing of the rise time and a higher amplitude than that of the 50 ohm-m soil because the resistance of the ground rod is higher, leading to a higher voltage for the same reference current. Figure 1: The voltage developed across a short 2 m ground rod for a typical subsequent surge current Long Ground Rods Long ground rods may be driven at commercial structures to lower the surge resistance to ground.
Long horizontal ground wires and grounding grids also fall into this category. These have been characterized using transmission line analyses; e. Verma  for ground rods and wires, and Gupta and Grecv  for grounding grids. As pointed out in Grecv, circuit-based models tend to overestimate voltages compared to transmission line models. But in that sense, circuit-based models are conservative. Transmission line analysis is necessary for very long grounding systems e.
For ground rods that are not too long e. The inductance of the ground rod is given in Verma as: 3 where l and a are as given in 1.
The initial shape of the curve in this case may be an artifact of the calculation. A longer ground rod 30 m has a large inductive effect on a subsequent surge. A Longer 30 m ground rod has a significant effect, but much less than it has in low resistivity soil. Nevertheless, some general conclusions can be drawn. Short ground rods are most simply modeled by a parallel RC circuit, where the resistance is determined by the resistivity of the soil and the capacitance can be estimated at about 3 nF.
Long ground rods are most simply modeled by a series RL circuit, where again the resistance is determined by the resistivity of the soil. Table 1 summarizes general conclusions about the dominant effects of ground rod length and soil resistivity. Rod type and soil resistivity Reactive effect.
IEC 61312-1 Protection Against Lightning Electromagnetic Impulse
Things You May Not Have Heard About Lightning and Grounds