ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • 9 Phoenix Contact But the voltage peaks that also occur on the supply and data lines due to indirect lightning strikes are usually signi cantly higher than the surge voltage strength of the equipment used in the charging devices and the surge voltage strength of the electric vehicle attached to them. When planning charging devices, however, malfunctions caused by lightning strikes are not the only thing that need to be taken into account; switching overvoltages from the lowvoltage supply system also play a part. Switching overvoltages occur frequently, but do not always cause immediate damage to the equipment. However, if switching overvoltages occur more frequently, then they can age electrical and electronic equipment prematurely. But individual switching overvoltages can also have an amplitude above the insulation or impulse withstand voltage of the equipment. Therefore, when higher voltage peaks occur due to lightning strikes or switching overvoltages, charging devices and the associated auxiliary equipment, including the electric vehicle itself, can become damaged or even destroyed. Overvoltages cause short circuits, among other things. The damage caused by short circuits in energy technology circuits is often more serious than damage that has been caused by the actual overvoltage event. When short-circuit currents are being directed to ground (ground leakage currents), conductive parts that are grounded can carry voltages that are dangerous if touched. Conductive parts of charging stations or conductive grounded parts of electric vehicles that can be touched can also be carrying dangerous voltages. The likelihood of voltages that are dangerous to the touch that were caused by voltage peaks with subsequent ground leakage currents can be effectively lowered by using surge protective devices. Usually, it is suf cient to protect charging devices and electric vehicles in such a way that they can survive indirect lighting strikes and switching overvoltages from the power grid without damage. Effective protection thanks to overvoltage safety equipment Overvoltage safety equipment effectively protects against transient events due to overvoltages resulting from lightning strikes (lightning surge voltages), overcurrents resulting from lightning strikes (lighting surge currents) and switching overvoltages. The following protective effects are achieved by using overvoltage safety equipment: • Surge currents caused by lighting are “redirected” so that the conductors do not overheat. • Overvoltages caused by lightning are limited for neighboring circuits in such a way that the insulation and electric strength of the equipment to be protected is not exceeded and there is no dangerous spark formation or short-circuiting. • Switching overvoltages are limited in such a way that premature aging of electronic devices is prevented to the greatest extent possible. The spatial design and the arrangement of electronic equipment in a charging park has a huge in uence on the respective load that can be expected due to surge voltages and surge currents. Therefore, a risk assessment should be carried out for each charging park. This is the only way to ensure that suitable surge protective devices are selected and the best-possible installation locations are found. If direct lightning strikes are to be expected, then powerful type 1 overvoltage protection equipment – referred to as lightning current arresters – should be included in the the potential equalization system for the power lines. If no external lightning protection is present or planned, then more costeffective type 2 overvoltage protection equipment – referred to as surge protective devices – are the optimal solution (Figure 3). In addition, numerous components are supplied with 24 V DC in the charging stations. The 24 V auxiliary voltage can be protected with type 3 overvoltage protection equipment, for example. In charging parks and at public charging stations, components for communication with a billing system or a building management system are also usually present. For this purpose, for example, an Figure 3 : SPD type 2: The VAL-SEC-T2-3S-350-FM devices from Phoenix Contact have been designed for grounded 230/400 V AC power supply systems. (continued on next page)
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