Electrical Substation and Overhead Power Lines

Posted on Oct 16, 2024 in Geology

1.1 Substation and Production

Substation Point

A set of all power generation plants.

Transmission Subsystem

Transformer and switching stations that elevate the voltage from the generating plants and transmit it through high voltage lines.

Distribution Subsystem

It receives energy from the electrical system in the form of a primary distribution network, processing stations, and secondary distribution networks.

Characteristics of an Electrical System

  • Number of phases
  • Service voltage
  • Frequency

Nominal Voltage

Conventional value of the effective phase voltage with which the line is designed and to which certain operating characteristics are referred. It is usually expressed in kV.

Characteristics of Power Lines

  1. Lines with nominal voltage greater than 66kV.
  2. Lines whose nominal voltage is between 66kV and 30kV inclusive.
  3. Lines with nominal voltages equal to or less than 30kV or greater than 1kV. The usual ones are: 20-66-132-220-380kV.

Network Distribution

Formed by two types:

  1. Overhead or underground lines of 45kV, 66kV, or 132kV.
  2. Medium and low voltage networks formed by:
    • Overhead or underground lines of 15-20kV.
    • MV/LV processing centers.
    • Overhead or underground twisted low voltage lines.

Electrical Distribution Network Structure

1. Network in MV

Formed by one or more MV lines that start from the existing transformation center in the area.

2. Linear Network

Distribution line with a maximum of 10 processing and distribution centers in MV, which require lines in LV.

3. Ring Network

Formed by a distribution line that closes on itself, 9 transformation centers, and the LV lines that it needs.

4. Multiple Ring Network

Formed by several ring networks, all connected to a substation to have its transformation available, with a maximum of 10 distribution centers with LV lines.

5. Normal Multiple Use Network

Formed by one or more normal uses connected at one end to a substation and at the other to other distribution centers.

6. Supported Use Network

Formed by a maximum of 6 distribution lines, all connected to 2 substations. If one circuit fails, it is supported by the corresponding distribution line in LV.

1.2 Overhead Power Line

Set of cables mounted at a certain height above the ground that transmit electrical energy.

Span

Distance between two supports of a line.

Sag

Maximum distance from a point of the conductor to the line joining two consecutive supports.

Supports

  1. Alignment Support: Supports conductors and overhead ground wires vertically and withstands transverse forces.
  2. Angle Support: Supports conductors and overhead ground wires at the vertices formed by two alignments, subjected to vertical and transverse forces.
  3. Anchorage Support: Its function is to provide firm points to the line, so that they limit the propagation of longitudinal forces. They are usually placed every 3km.
  4. End of Line Support: They must resist the longitudinal force of the line in both directions of the conductors and overhead ground wires.
  5. Special Supports: Their functions are different and include: line crossings, crossing of urban roads, telecommunication panels, etc.

Forces to which the supports are subjected

  • a) Vertical Forces: Mainly due to the weight of the conductors.
  • b) Transverse Forces: They arise from the action of the wind on the support when the conductors are at an angle.
  • c) Longitudinal Forces: Originated by the longitudinal attraction of the conductors.

Metal Poles

There are two types of poles and both are manufactured with rolled steel profiles, with a thickness of not less than 4mm and their yield strengths ranging from 275-355daN:

1. Pressed Poles

Formed by two sections, assembled by bolts and each forming an angle formed by 4 uprights joined at the top by welded gussets. The top section is 6m, the bottom one can be 6m or open so that braces of 10 to 12m total height can be placed. Nominal forces: P400, P750, P1250.

  • a) Height: P400…
  • b) Braced: Combining different types of head and braces and designating each type by its profile “r” or “s” (rigid or suspended).
  • c) Spreaders: Flat, vaulted, and head.
  • d) Foundation: Made of reinforced concrete, they are calculated with a safety factor of 1.5.

2. Lattice Poles

Divided into two sections: 1-Up to 4500daN useful force at the tip, 2-With useful force at the tip of 7000 to 9000daN. These poles are made up of a head (C), intermediate sections (E), and anchor sections (A).

  • a) Type: The poles are calculated considering their elements subjected to traction or compression forces.
  • b) Heights: It is the distance from the tip to the inner end.
  • c) Braced: Adequately combining the arms and head, they are braced with all the different types of bracing: horizontal, triangle, trefoil, hexagon, rectangle, vault, horizontal vault.
  • d) Spreaders: Types: flat, vaulted, head.

Spreaders for Concrete Poles

  • Slider for rigid insulators.
  • Crossarm for suspended insulators.

Anti-climbing Devices

They are placed at the bottom of the poles to prevent climbing them, and they carry a warning sign of electrical hazard.

Electrical Hazard Signs

Made of galvanized steel sheet, aluminum, stainless steel, etc., 1mm thick, with the logo and text on electrical hazard, perforated, with dimensions 250x220mm.

Concrete Poles

The most important characteristic of concrete poles is their resistance to compression, which ranges between 230 and 430kg/cm2, depending on the water content. (They can be made of reinforced concrete, vibrating, spinning, prestressed). At the top (head) they have a series of holes where the fittings are attached.

Foundations

They are made of concrete monobloc whose resistance will not be less than that of the support, verifying the safety factor.