Low Voltage Distribution Networks: Aerial and Underground
The distribution network in Low Voltage (LV) begins at processing centers where Medium Voltage (MV) is passed to LV. This network is regulated by Article 8 of the Electrical Regulations for LV and is defined as a set of conductors that, assuming a processing center, runs along the entire supply area of influence.
Types of LV Distribution Networks
LV distribution networks can be one of two types:
- Aerial Network
- Underground Network
Aerial Networks
In aerial networks, conductors can be woven or braided and tensioned.
Braided Aerial Network
The network consists of four cores together in a braid, with no contact between them to avoid a short circuit. The neutral conductor may also serve in some facilities as the upholder of the twisted beam. In braided networks placed on facades, drivers are not subjected to any mechanical stress. The network runs on the facades of buildings across empty spaces with a basis adapted to the layout of moorings. It is practically the only type used in areas with a high density of population in a confined space. However, it requires more length in a tensioned beam, making it more expensive.
Tensioned Aerial Network
The network is stretched and braided on supports, where the beam is installed on a tense setting. It is used in rural areas. Supports are currently made of concrete poles. The separation between them must be between 4m and 10m. Tensioning is determined using a table that takes into account temperature, weight, and length. The fixing can be supportive or neutral to the guarantor cable.
Underground Networks
Underground networks are accustomed to being built in densely populated areas for their safety and aesthetic considerations. This network starts at an underground transformer station and runs through roads and pavements to a depth of between 75cm and 80cm. Conductors can be copper or aluminum and are protected by polymeric compounds against corrosion. Underground networks are made with insulated wires in conduits that run through public lands and confined areas (sidewalks). Their stroke is designed to be as straight as possible to have references on facades and reduce costs. Trench types depend on whether the cables are buried directly, run through tubing under the sidewalk, or if a casket is used for registration.
Ice Load Zones
For the purposes of loads due to ice, the following zones are defined:
- Zone A: Less than 500m altitude above sea level.
- Zone B: Between 500 and 1000m altitude.
- Zone C: More than 1000m altitude.
Earthing Schemes
TN Scheme
TN schemes have a feeding point, such as the neutral, which is connected to the ground, and bodies of the receiving facility are connected via protective conductors. There are three types of TN schemes:
- TN-S: The neutral and protective conductor are different throughout the whole scheme.
- TN-C: The neutral and protective functions are combined into a single conductor throughout the whole scheme.
- TN-C-S: The neutral and protective functions are combined into a single conductor in a part of the scheme.
Letter Coding:
- 1st letter: Refers to the situation of food on earth.
- 2nd letter: Refers to the situation of the masses of the reception facility on land.
- Other letters: Relate to the situation of the neutral conductor and protective conductor.
TT Scheme
TT schemes have a feeding point, usually the neutral, connected directly to the ground. The masses of the reception facility are connected to separate ground from the outlet and feeding ground.