Smart buildings: lightning and transient overvoltage safety

Smart buildings are particularly vulnerable to the destructive effects of thunderstorms, due to the wide variety of interconnected automatic systems (such as lighting, temperature control, multimedia systems, telecommunications, security, etc.). Therefore, any surge that penetrates the structure, not only through the power supply lines but also through the data lines, can cause damage to a multitude of sensitive electronic equipment such as computers, alarm systems, transducers, programmable logic controllers, audio-visual equipment, etc.

Smart buildings are becoming increasingly widespread as a result of technological advances that maximise building efficiency and, in addition, improve the comfort of users, the productivity of the companies housed in them and, therefore, their overall value. However, due to networked components that rely on a constant supply of power and data for their continuous operation and availability, they are particularly vulnerable to lightning strikes and surges in general. Equipment failure in a smart building could collapse all interconnected systems and bring buildings and work environments to a breakdown, with associated costs.

The National Fire Protection Association (NFPA) in its 2020 Safety Standard for the Installation of Lightning Protection Systems1 contains an annex dedicated to smart buildings. It distinguishes between two types of installations: equipment rooms or control rooms and distributed equipment (distributed control). The first type generally includes computers/servers, programmable logic controllers, alarm controls, telecommunications equipment and the like. This NFPA Standard stresses that it is essential to apply the lightning protection zone concept to these control rooms, in particular, to ensure equipotential bonding that keeps the earths at the same voltage, so as to prevent harmful currents from flowing through sensitive equipment.

Distributed equipment typically consists of remotely operated controllers, relays, switches with motor or lighting, sensors, cameras, computers, and controller inputs, among others. NFPA focuses on the protection of distributed control by means of surge arresters installed at the power inlet/outlet of smart buildings, as well as at the transition between lightning protection equipotential zones. In this regard, it points out that the equipment most affected by transient surges are cameras, motors that drive access doors and pumps, as they are usually located far away from the structure, but have their own power and signal input.

However, in addition to equipotential bonding and surge arresters, buildings must have adequate external lightning protection. For the protection of such a critical structure as a smart building, Aplicaciones Tecnológicas has the SMART DAT CONTROLER® SUPERVISOR, an advanced lightning protection system comprising a lightning arrester with Early Streamer Emission (ESE) device, the DAT CONTROLER® REMOTE, and remote monitoring via the Internet of Things (IoT). The smart sensors of the SMART DAT CONTROLER® SUPERVISOR monitor key parameters of the lightning protection installation such as the operating status of the ESE device, the continuity of the down conductor and the earth resistance. In addition, this innovative LPS (lightning protection system) also provides information (number and characteristics) of the impacts intercepted by the lightning arrester with the Early Streamer Emission device.

In the following, measures covered in the Smart Buildings Annex of the NFPA Standard, i.e. equipotential bonding and surge arresters, will be discussed in more detail.

Lightning protection equipotential zones in Smart buildings

The general concept of protection for smart structures is concentric protection establishing successive lightning protection zones (LPZ). These zones will be determined by equipotentialisation and surge protection, lightning protection techniques recommended especially for smart buildings in the NFPA Standard.

LPZs, according to UNE-EN 62305-1, are zones in which certain electromagnetic conditions are defined2. Each of these zones should function as a single equipotential unit. This is achieved by interconnecting all metallic surfaces with the earth conductors. In this way, current flow from an external location to the LPZ is prevented, either by external faults in the AC or DC systems or by the introduction of lightning current into the building. In addition, the equipotential bonding of the metallic elements reduces electromagnetic field disturbances and their associated dangers. In Aplicaciones Tecnológicas S.A. we have the appropriate material to guarantee the equipotential bonding of the LPZ of smart buildings.

It is also recommended that the signal and power input to the relevant structure or LPZ be made through a single point, preferably close to the earthing point. This favours the installation of surge protectors, shortens the length of the grounding conductor (which in turn reduces impedance and voltage differences) and facilitates the implementation of equipotential grounding which reduces the likelihood of unwanted ground paths. In any case, to avoid overvoltages, each zone must be protected by suitable devices on all lines entering or leaving it.

Transient surges protection

Surges are very short duration voltage spikes that are introduced into equipment via power, telephone, television or data supply lines. The damage that surges can cause in each LPZ is different, so protection must be based on the risk present and the surge withstand capability of the equipment to be installed in that area. Surge protection helps to maintain continuity of service and reduce the likelihood of safety incidents to an acceptable level for people and property.

Surge arresters are installed at the current input/output at transitions from one zone to another and on sensitive equipment inside equipotential LPZs. The particularities of the equipment connected to each line must be taken into account in order to optimise the selection of surge arresters. Generally, a single commercial overvoltage protective device does not meet all the required discharge current and residual voltage characteristics. The higher the current carrying capacity of the device, the higher the residual voltage. Therefore, several surge arresters that are well-coordinated are required, i.e. that act in stages with several sequential protection stages so that they are able to withstand the currents associated with the lightning strike and to leave a residual voltage that is not harmful to the installed equipment.

The first or strong transient surge protection protects against the effects of direct lightning strikes. These elements consist of spark gaps, gas dischargers or varistors which are characterised by the fact that they remain completely open during normal current. If the breakdown voltage is exceeded, they short-circuit and divert the entire current to earth. When the high voltage level disappears, the components return to the rest state and reopen the circuit. The ATSHIELD series of transient surge protectors from Aplicaciones Tecnológicas S.A. combines robust elements with limiting components, achieving a high absorption capacity of the direct lightning current together with a low residual voltage.

The second protection is thinner than the previous one and usually consists of varistors, which are variable resistors. In general, they are faster than spark gaps, but they have the disadvantage that at normal voltages a certain impedance is produced which causes small current leakages. The ATSUB and ATCOVER series of Aplicaciones Tecnológicas S.A. are totally suitable for this second protection. Specifically, the ATSUB series withstands currents of tens of kiloamperes, reducing the surge to levels that are not harmful to the equipment. The ATCOVER series, in addition to being robust and complete, protects all phases quickly and efficiently, in common and differential mode, leaving a low residual voltage. It should be noted that if there is not 10 metres of separation cable between the ATSHIELD and ATSUB/ATCOVER surge protectors, a decoupling inductor such as ATLINK should be installed.

The third protective barrier is usually formed by transient suppressor diodes which are very fast elements that leave very low residual voltage. However, it must be taken into account that they are incapable of withstanding currents greater than a few amperes. In Aplicaciones Tecnológicas S.A. we have the ATSOCKET and ATPLUG protectors, as well as the specific ones to protect telecommunications and data lines ATFONO, ATLAN and ATFREQ.

Telephone and data lines, which are present in considerable numbers throughout smart buildings, can act as conduits that introduce surges into the structure and equipment. It should be noted that, by definition, these buildings have a variety of devices that control electronic equipment from remote distances using data lines. In addition, these data communication lines are connected directly to the integrated circuits of sensitive equipment, so that any overvoltage can cause severe damage to the tracks and components, leading to degradation or destruction of the equipment, including stored data. Also, telephone lines are connected to sensitive and important equipment inside and outside computers. Therefore, the ATFONO (for analogue telephone lines, ADSL, ISDN) and ATLAN (for computer lines and internal computer network) series are particularly relevant for protection against transient surges in such buildings.

Smart buildings, with their peculiarities derived from the wide variety of highly sensitive and networked electronic equipment whose failure implies the paralysis of the activity of the working environments, require protection against lightning and its destructive effects. If you would like more information about Aplicaciones Tecnológicas’ solutions for the protection of Smart buildings, you can contact us by following this link.

References

  1. National Fire Protection Association (NFPA). NFPA 780 Safety Standard for the Installation of Lightning Protection Systems. (2020).
  2. AENOR. UNE-EN 62305-1 Protección contra el rayo Parte 1: Principios generales. (2011).