Enclosures play an extremely important role because if they cannot withstand the earthquake, the entire system is going to fail. This makes earthquake protection for enclosures a key factor in all the relevant standards. However, this aspect can never be considered in isolation, but rather the surrounding building and all the installed components must also comply with the relevant requirements as well. Thus a suitable enclosure alone will not suffice if the system needs to remain operational after, or even during, an earthquake. In addition, the installed components must also meet the requirements of the appropriate standard and the functioning of the entire system must be proved under test conditions.
In order to evaluate the relevance of earthquake protection for electrical installations, an overview must first be established of the damage that can potentially occur in an earthquake, including any consequential damage that might arise if an electrical system fails. Damage to buildings is usually the focus of attention following an earthquake. Depending on the kind of building involved, the values for the systems installed in it are often higher than for the structural elements themselves. It makes sense, therefore, to look beyond the earthquake-resistance of the building alone and to also consider the potential requirements regarding its systems in the case of an earthquake.It is particularly important that the installations of critical, safety-relevant infrastructures, such as in nuclear installations, remain operational even after high-magnitude earthquakes. This calls for a very extensive range of measures, which are beyond the scope of this white paper. A high level of systems availability, and thus robust protection against earthquakes, is also particularly vital for telecommunications and IT. At the same time, the ability of installations to remain operational for a given time or to resume service quickly are also important issues following an earthquake.
The frequency of the vibrations that occur during an earthquake generally ranges between 0.3 Hz and 50 Hz. The stresses these vibrations exert on a switchgear system can cause both malfunctions and structural damage to the entire system. Malfunctions can be remedied with little delay, so a switchgear system can be put back into service relatively quickly following an earthquake. This might typically involve a loose contact or temporary short-circuit that is interrupted by the installation’s safety systems. More disruptive damage might include the dislocation of components from an enclosure’s support rail or mounting plate. Serious damage to the switchgear system generally causes a protracted interruption to the energy supply – say, if the earthquake were to move an enclosure, perhaps dislodging it from its anchoring or even tipping it over.
Measuring technology for earthquakes
Scales of magnitude are based on measurements taken by seismometers, which measure the local vibrations in the Earth’s surface in terms of speed, acceleration and displacements. Calculations using these measurements can indicate the strength of the earthquake. The best-known scale of magnitude is the Richter scale, which was developed in the 1930s and is still used today for this purpose. The magnitude according to the Richter scale is calculated using measurements taken by a special kind of seismometer near to the earthquake’s epicenter (at a distance of 100 km), which is why it is also frequently called the ‘local magnitude scale’.