Electrical Distribution Networks in Low Voltage (LV)

Posted on Oct 27, 2024 in Technology

Air Network Components

The electrical distribution air networks in LV consist of the following components: conductors, insulators, and supports.

Conductor Features

Conductors in these networks are typically made of copper or aluminum alloys with adequate electrical and mechanical properties.

  • Insulated Conductors: These conductors have a coating that provides resistance to the elements. The voltage is 0.6/1kV, and the minimum cross-section is 16mm2 for copper (Cu). They are used in LV air networks, perched on building fronts or stretched over supports.
  • Neutral Wires: Neutral wires are often made of an aluminum (AL) alloy with silicon and magnesium, called “Almelec,” with a rating of 54.6 and a cross-section of 80mm2. The roof insulation is made of a polyethylene layer with an easy-separation mesh.
  • Conductor Requirements: Conductors must be weather-resistant and have a minimum breaking load of 410kg. The characteristics of the cores are determined by the cross-section, the permissible current in continuous operation, and the maximum short-circuit current.

Insulators

Insulators are made of porcelain, glass, or other suitable materials. The conductor is attached to the insulator using a retention wire of the same material as the conductor. The main function of power line insulators is to prevent the passage of electrical current from the conductor to the support.

Causes of electrical conduction malfunctions in insulators:

  • Through the Insulator Body: Due to high leakage current (IF = V/R).
  • Surface Conductivity: Due to moisture or dirt deposited on the insulator. To prevent this, the insulator has a very long external line.
  • Insulator Body Piercing: Due to a manufacturing defect (RD = V/d).
  • Flashover Through the Air: Arcing occurs between the conductor and the insulator support, or through humid air, overcoming the dielectric strength.

Construction Characteristics of Insulators

  • A. Glass Insulator: Obtained from a mixture of sand fused with sodium salt at 1300°C. Glass is a widely used, low-cost material, but it is fragile and has a high expansion coefficient. Dielectric breaks should be designed to facilitate fault location.
  • B. Porcelain Insulator: Obtained from a mixture of kaolin and quartz baked at 1400°C, with a thickness of up to 3cm to obtain a homogeneous mixture. Externally, a layer of enamel is applied to prevent the accumulation of moisture, dust, and other substances.

Classification and Use of Insulators

  • A. Support Insulator: Used in LV lines and MV lines up to 66kV. The conductor is attached to the head or neck of the insulator.

Ground Facilities

All LV installations have grounding to limit over-tensions. According to regulations, all metal parts of an installation not normally under tension, but likely to be energized in case of failure, lightning, power surges, etc., must be grounded. Examples include:

  • High and low voltage masses
  • Display or protective lattice
  • Metallic sheath or screen wire
  • Metal processor enclosures
  • Metal frame inside the building

The following fixtures will also be connected:

  • The transformer neutral
  • Auto valve
  • Elements of earth leakage breakers
  • Ground unloaders and limiters

Insulation Level and Control Process

Insulation levels:

  • 1st Level: Valves or rods must act, diverting over-voltage to ground.
  • 2nd Level: An electric arc forms between busbar conductors, overcoming the isolation distance.
  • 3rd Level: Transformer insulation preserves and protects against over-voltage.

Switching device control process:

  • Off (down) LV switch, circuit breaker (up) connection.

Classification of LV Electrical Distribution Networks

The distribution network comprises conductors and supports covering the entire supply area. The term “rush” refers to the installation of the distribution network that feeds a subscriber.

Networks can be grouped into two types:

  • Air Network: Conductors are either attached to the facade of buildings or strung between supports. Air networks can be twisted, braided, or tensioned.
  • Underground Network: Conductors are laid underground.

Standard components and materials are used for LV energy distribution. The conductors employed can be insulated.

Air Networks

LV overhead networks can be:

  • A. Braided Posada Network: Ideal for tight spaces.
  • B. Tensioned Braided Network: Used in rural areas, where conductors run along agricultural land. They are installed using specific tensioning methods and supports, usually concrete poles.

The setting can be done with a neutral conductor.