It is related to good engineering of protection. Protection measures, adopted to reduce such damages and relevant consequential loss, should be designed for the defined set of lightning current parameters against which protection is required. In standard IEC 62305 this set of lightning current parameters is defined as the lightning protection level (LPL). The required protection measures and the relevant LPL are determined by performing a risk assessment according to the procedure reported in IEC 62305-2.
Planning and coordination of protection measures begins with an initial risk assessment to determine the required protection measures needed to reduce the risk to, or below, the tolerable level. When possible, protection measures should be selected taking into account both technical and economical aspects; this is not the case for a LPS, which is the only measure to reduce the physical damage.
As far as the protection measures to reduce failure of electrical and electronic systems are concerned, those of a preventive type are structural protection measures that it is generally possible to implement only at the stage of erection of the station and at the installation of electrical and electronic systems.
Even the design and installation of such measures is a heavy task and their cost may be high; however, it is recommended when high reliability and availability of protection is required, as is the case for large unattended stations, remote from maintenance centers and located in mountainous regions, with difficulty of access, especially in winter.
Therefore, the following steps should be carried out in implementing protection measures to reduce the failure of electrical and electronic systems.
1. An earthing system, comprising a bonding network and an earth termination system, should be provided.
2. External metal parts and incoming services should be bonded directly or via suitable SPDs.
3. The internal system should be integrated into the bonding network.
4. Spatial shielding in combination with line routing and line shielding may be implemented.
5. Requirements for a coordinated SPD protection system should be determined.
Following this, the cost–benefit ratio of the selected protection measures should again be evaluated and optimized using the risk assessment method.