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 overvoltage were created. 

The different protections against overvoltage

There are three main families of protection :

Energy networks protections:
• Protect all the electrical material against the overvoltage from the energy network.
• Divided in class according to the protection required.
• Protections installed in parallel.
• Protections equipped with varistors and spark gaps

VLV protections:
• Divided in class to the protection required.
• Exist for all types of VLV network or transmission.
• In series on the installation.
• Equipped with transil diodes and tripolar spark gaps..

Coaxial protections:
• Existing products for specific applications (GSM, TV, UHF systems…).
• Bi-directional products equipped with passive components.
• Installed in series on the incoming line near to the equipment.

Choice of the surge protective devices

Common rules valid for all ranges in order to ensure the safety of the people and the working of the products under best conditions:
→The choice of the Up level of protection depends on the electric sensitivity and also on the existence or not of an ESE lightning conductor on the building.
→ For Telecom and coaxial protections, it is necessary to take more into account the Up level of protection, the frequency of operation (Band-width), 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 IEC 61-643 standard.
→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 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 optimized, 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 50 cm.

Earthing system

• Any separate ground connection.
  – If in an electric board or a cabinet, and if 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 increasingly frequent presence of sensitive electronics makes electrical equipment additionally vulnerable to transient overvoltage associated with lightning.

Compared to other possible origins (industrial overvoltage, network overvoltage, electrostatic discharges, …), transient overvoltage from atmospheric origins are the most dangerous for equipment and for electrical or electronic installations.

Caused by enormous energies generated in a very short time, it can be provoked by a direct lightning strike on 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 equipment and ground must be achieved. Installation of surge protection devices are also necessary to absorb the energy. 

Overvoltage 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 main part of lightning strike energy is “conducted” by the network.

Overvoltage 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 overvoltage 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 overvoltage 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

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Energy network protection 

The choice of the surge protective devices to set up, depends on the behaviour of the electric material to protect. The characteristics of the surge protective devices were studied to protect all levels of an electric installation.

There are 4 classes of shock voltages: 1.5 kV,
2.5 kV, 4 kV and 6 kV. Belong to a class depends on the electrical resistance to the material to the overvoltage.

Some important values :

Uc: the maximum voltage under continuous operating conditions.
• Up: the residual voltage in kV transmitted by the equipment when these protection devices are kept to their nominal current.
• In: the nominal discharge current. It is the peak value of a current in the 8/20 μ wave form, flowing in the overvoltage arrester.
• Iimp: Maximum discharge current in wave 10/350.
• Un: the nominal operating voltage. It characterizes the simple voltage between phase and neutral.
• Imax: discharge current that the overvoltage arrester can withstand once. 

Rules of installation

The surge protective device will be inserted in parallel the shortest possible path on the power supply concerned.
– In complement of the integrated thermal disconnection, a protection against the short-circuit at the end of life will be installed, upstream of the connection of the surge protective device. The diagram of connection will be given, according to whether the priority is given to the continuity of service or that of protection.
– It is possible to obtain at the same time the continuity of service and the continuity of protection, thanks to the use of several identical surge protective devices, assembled in parallel, and equipped each one with a deconnector.
– In partnership with the modular surge protective devices, one will choose either of the fuses or of the circuit breaker. This insertion must hold account of the number of poles to protect and the current from possible short-circuit at the point considered.
It is obligatory to carry out a protection with surge protective device of the type I in the case or the structure would have a lightning conductor.
The section of conductor obligatory for the surge protective devices type 1 is 10 mm2 and 4 mm2 for types 2 and 3.

F1, F2: fuses or circuit breaker
SPD: surge protective device
TT Earthing system: RCD obligatory upstream of the surge protective devices type “C1”
BP: main terminal of earthing
Total length d1+d2+d3 the shortest possible
(< 50 cm recommended F1, F2 : fuses or circuit breaker

Rules of installation of telecom protections 

These protections are installed in series at the entrance of the installation, on the customer side of the network termination. For maximum protection they are placed close to the equipment if the equipment is located far from the network termination (30 m or more).
– The connection to the earthing system is compulsory to ensure proper operation of the protection.
– Respect the incoming/outgoing wiring direction.
– Do not connect in parallel incoming and outgoing lines.
– Check proper wiring of the earthing system.
– The earth conductor is connected with the main earth of the installation according to the rule of the shortest possible path.
– It is recommended to have spare protection units to be able to quickly replace any faulty ones.
– Products shall never be opened in order to avoid any destruction or failure and to keep the warranty running.

Rules of installation for coaxial protections 

This type of protection is installed in series on the coaxial line located nearby to the equipment to be protected.
– It can either be mounted on the equipment itself or outdoors and also in a penetration mode.
– The connection to the network will be direct with connectors of the product.
– Spark gap based coaxial protectors are connected to the earthing system by spade terminals for conductor from 2.5 to 6 mm2 and the quarter wave type protectors by spade terminal from 6 to 25 mm2.
– Some models of coaxstops are provided with a cross-partition mounting (IEMN models).
– Check that the rated voltage and maximum power of the protection is coherent with the network.
– The end of life of a protection is reported as the loss of the signal or as a communication interruption.
– Products shall never be opened in order to avoid any destruction or failure and to keep the warranty running.
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