Overvoltage protections

The indirect effects of the lightning are numerous. For this reason we have to protect all the electrical, electronic and computer elements. That is why all the products of protection against overvoltages were created.

Choice of the surge protective devices

Common rules valid for all ranges in order to ensure the safety of the people and the operation of the products under best conditions:

---The choice of the level of Up protection depends on the electric sensitivity and also on the existence or not of a PDA on the building.

---For Telecom protections and coaxial, it is necessary to take into account more the level of Up protection, of the frequency of operation (Band-width), of the attenuation, and the voltage of the communication network

--- The choice of the surge protective device will be facilitated by the markings made compulsory by standard IEC 61-643.

---The end of life of the surge protective devices needs to be studied in order to ensure the good working of the material (requiring additional disconnecting elements for energy networks surge protective devices).

Connection equipment

--- The cables should run separate from the other conductors and the earthing system should have the shortest possible route to the equipotentiality bar or the body of the cabinet.

--- The path of the conductors needs to be optimised paying attention to the fact that the input wires on the surge protective device be distinct from those of the output.

--- The output protected by an overvoltage arrester must be taken to the same terminals on the surge protective device and breaking device installed for end of life protection..

---The total length of the connections, breaking device and protection device must not exceed 50cm.

Earthing system

--- Any separate ground connection.

---If in an electric board or a cabinet,and the link to the general ground is too long, an intermediate ground terminal box shall be installed.

---One ground connection per building or per protected installation is required.

---To optimize the installation, the resistance of this ground connection must be the lowest possible HF impedance.

---A check should be made to ensure that there are no connections within the same building or electrical cabinet to separate ground connection distributions with remote equipotentiality devices.

All these installation rules are valid for all protections.

The transient overvoltages

The increasingly frequent presence of sensitive electronics makes electrical equipment additionally vulnerable to transient overvoltages associated with lightning.Compared to other possible origins (industrial overvoltages, network overvoltages, electrostatic discharges, …), the transient overvoltages from the atmospheric origins are the most dangerous for the equipment and for the electrical or electronic installations. Caused by enormous energies generated in a very short time, it can be provoked by a direct lightning strike on the electrical network (phone lines etc …), by induction or by ground rising conductors.Insulation measures compulsory under the standards of equipment manufacture are not sufficient (IEC 610000-4-5 : immunity of the equipment). The equipotentiality of the equipment and ground must be achieved.  Installation of surge protection devices are also necessary to absorb the energy.

Overvoltages by conduction

When there is a direct lightning strike on an electrical line or a tower , the current can propagate and reach all the installations distributed by the line, even if they are situated at several kilometres from the impact point. These currents are all the more dangerous as the main part of the lightning strike energy is "conducted" by the network.

Overvoltages by induction

All the metallic elements situated in an area very near a lightning strike act as antennas, which capture by "induction" the sudden variations of the electromagnetic radiation induced by the lightning. Transient overvoltages and currents appear then on all the equipment which is connected with it, of which the effects are proportional to the strength and the nearness of the lightning strike.Even if it constitutes a means of protection against the direct impact of the lightning, burying electrical networks does not guarantee their 
protection.

Ground rising conductor

When there is a lightning strike close to a building, the propagation of the current through the earth can reach the building and cause a local rise in potential of the electrical earthing of the installation, which is connected to the body of any equipment. Differences of potential appear then between equipment bodies and networks to which they are connected. Without any protection, these overvoltages are at the origins of "rising" strong transient currents which can be very dangerous.

One part of the lightning current is dispersed by the lightning conductor earth, another part by the installation earth, this is the ground rising conductor.