Air Network Conductors and Mechanical Calculations

Posted on Oct 29, 2024 in Technology

Drivers

Drivers in Air Networks

The drivers used in air networks will be copper, aluminum, or other materials or alloys with appropriate electrical and mechanical properties and will preferably be insulated.

Insulated Conductors

The insulated conductors shall be rated for not less than 0.6 / 1 kV. The minimum allowable aluminum conductor size is 16 mm2, and for copper, it is 10 mm2.

Conductors

Bare conductors are resistant to weathering. Their minimum breaking load will be considered as 410 daN. Bare conductors insulated for a rated voltage less than 0.6 / 1 kV will also be considered.

Insulators

Insulators are made of porcelain, glass, or other insulating materials capable of withstanding equivalent weather conditions, especially temperature changes and corrosion. Fixing the insulators to their supports is done by threading or cementing them to a base made of substances that do not attack any of the parts and do not suffer volume changes that may affect the insulators or the security of their attachment.

Support

Supports may be made of steel, concrete, wood, or other materials with proper authorization from the competent authority.

2. MECHANICAL CALCULATION

Permanent Loads

Permanent loads shall be considered as vertical loads due to the weight of different elements: conductors, insulators, clamping accessories, and supports.

Overload in Wind Pressure

Consider the following overload in wind pressure:

  • On drivers: 50 daN/m2
  • On flat surfaces: 100 daN/m2
  • On cylindrical surfaces of supports: 70 daN/m2

Surge Driven by Ice

For the purpose of surge driven by ice, classify the country into three zones:

Zone A:

Located within 500 m of altitude above sea level. No overload due to ice will be considered.

Zone B:

At an altitude between 500 and 1000 m. Bare wires will be considered subject to the overhead of an ice cuff value of 180 π D g per meter, where d is the conductor diameter in mm. In bunched cables, the overhead is considered to be 60 π d grams per meter, where d is the diameter of the cable in the beam in mm. For calculation purposes, the beam diameter is considered to be 2.5 times the diameter of the phase conductor.

Zone C:

Situated at an altitude above 1000 m. Bare conductors are considered subject to the overhead of an ice sleeve value of 360 π D g per meter, where d is the conductor diameter in mm. In bundled cables, the overhead is considered to be 120 π d grams per meter, where d is the diameter of the cable beam in mm. For calculation purposes, the cable beam diameter is considered to be 2.5 times the diameter of the phase conductor.

2.2 Drivers

2.2.1 Maximum Permissible

The maximum allowable tensile load on drivers should not exceed the ultimate load divided by 2.5, considering the worst-case scenario of the following:

Zone A:

  1. Driven by the action of its own weight and wind load at a temperature of 15°C.
  2. Subject to the action of its own weight and wind load divided by 3, at a temperature of 0°C.

Zone B and C:

  1. Driven by the action of its own weight and wind load at a temperature of 15°C.
  2. Subject to the action of its own weight and load of ice for the area at a temperature of 0°C.

Maximum Deflection

The increase resulting from the comparison between the two scenarios for the climate zone is considered as a third temperature hypothesis (valid for all three zones). This consists of considering drivers under the action of their own weight and the maximum expected temperature, taking into account the climate conditions and the network service. This temperature is not below 50°C.

3. PERFORMANCE FACILITIES

The insulated conductors rated for a voltage of 0.6 / 1 kV (UNE 21 030) may be installed as:

3.1.1 Perched Cables

Perched directly on walls or facades with clamps attached to them and resistant to weathering. Drivers will be adequately protected in places where they may suffer mechanical damage of any kind. A minimum height of 2.5 meters to the ground shall be observed. In the vicinity of openings in walls, the following minimum distances should be observed:

  • Windows: 0.30 meters to the top of the opening and 0.50 m to the bottom and side edges.
  • Balconies: 0.30 meters to the top of the opening and 1.00 meters to the side edges of the balcony.

Take into account the existence of protrusions or shelters that can facilitate the sitting of the drivers. In these cases, a decrease in the distances mentioned above may be admitted.

3.1.2 Tensioned Cables

Guarantor neutral wires may be divided between special pieces placed on props, facades, or walls with adequate mechanical stress.