What is SPDA (Lightning Protection System)?

Do you know what is SPDA? What is the SPDA for? And what is the importance of SPDA? If your answer is no or if you have any questions about SPDA come and learn with us a little more about this subject because in this article we will cover what is SPDA, the main characteristics of an SPDA, applications of the SPDA and types of SPDA, come on guys!

What is SPDA?

The acronyms SPDA stand for a system of protection against lightning strikes, these systems serve to protect buildings, antennas, industrial installations, tanks, pipes, and people against lightning strikes and their effects. Lightning protection systems (SPDA) are composed of devices installed at the highest points of installations and structures, they provide a path to earth offering the lowest possible electrical resistance, in order to offer a path for current created by lightning. flow towards the earth, without damaging equipment or structures, besides protecting people inside the installation.

Basically, the objective of the SPDA is to dissipate this dangerous electrical current to earth, directing the current through the safest possible path, thus minimizing or canceling its impacts.

The use of SPDA does not prevent the incidence of lightning strikes at the site, the discharges are natural phenomena caused by the friction of clouds in the sky, this friction generates an electrification effect of great potential difference, so it is impossible to cancel the indecency of the discharges, more through SPDA´s we can minimize its effects on the installations, constructions and protect the people sheltered there.

Take the example of the complete system:

Formation of electrical discharges and operation of the SPDA.

When do we use SPDA?

The regulatory norm NR10 establishes that every establishment that has an installed power greater than 75KW, must have and maintain the medical record of electrical installations (PIE), within this documentation must contain the inspection report of the SPDA system and electrical grounds. In this way, companies are responsible for building and maintaining the SPDA system in operation.

The use of SPDA is a requirement of the fire brigade in buildings over 30 meters high and commercial and industrial facilities, with more than 1500 m² of built area, it is also a requirement in areas destined to explosive and flammable deposits, and also in other buildings at the discretion of the Fire Department, whenever the need for dangerousness is justified; the SPDA must comply with criteria of reliability and safety, as it prevents explosions and fires, especially in dangerous environments such as gas stations.

What makes up an SPDA, and what are the types of SPDA?

The SPDA installation standard is regulated by the Brazilian Association of Technical Standards (ABNT), through NBR 5419 the main objective of the standard is to prevent and minimize fires, explosions, material damage and risk of death to people and animals due to the effects of electrical discharges .
There are currently three design methods:

  • Faraday’s cage method ;
  • Franklin’s method (limited according to height and protection limit);
  • Rolling ball or fictitious ball method.

The Faraday Cage method consists of installing a system of captors formed by horizontal conductors interconnected in the form of a mesh. This method is widely used in industry for the protection of warehouses and buildings, since the laying of cables in the structure becomes the receiver of lightning. The use of this type of SPDA is based on Faraday’s theory, according to which, the electric field inside a cage is null, even when a high value current passes through its conductors, but for this it is necessary that the current is distributed evenly across the surface. The shorter the distance between the conductors of the grid, the better the protection obtained (NBR 5419/2005).

Observe the application of the faraday cage:

Person being protected by a Faraday cage.

The Franklin method uses the famous lightning rods, these being the Franklin type. They are installed to protect the volume of a cone, where the captor is at the apex and angle between the generator and the center of the cone, varying according to the level of protection and the height of the building. Due to its limitations imposed by the standard, it becomes less and less used in buildings, being ideal for small buildings its limitations are due to its height protecting a maximum height of 45 meters or 15 floors, having an arrow for protection of about 25º. (NBR 5419/2005).

Observe the FranKlin type lightning rod as shown:

Protection radius for Franklin type radius.

The rolling ball method is the most recent of the two mentioned above and consists of rolling a sphere through the entire building. This sphere will have a defined radius depending on the Protection Level. The places where the sphere touches the building are the places most exposed to discharges. In short, we can say that the places where the sphere touches, we must understand that the ray can also touch, so these need to be protected by metallic elements (Franklin sensor or metallic conductors). Another way to protect the facilities is to use the combination of these methods, being allowed by NBR 5419.

All three types of lightning protection systems (SPDA systems) require a grounding mesh containing interconnected rods and conductors for the dissipation of electrical current. The number of rods fixed to the ground depends on the resistivity of the ground, the height of the structure to be protected, and the area built, the greater the need to use a larger number of ground rods.

The use of the lightning protection system is very important for the protection of people and material heritage, in addition to being a requirement for standards, it has a complete technical standard that specifically addresses SPDA. There is a series of details not covered in the article, we advise that whenever services or projects in SPDA are carried out, consult NBR 5419 for further details. To learn more about electrical grounds, watch the video below:

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