Réseaux souterrains

There are two types of distribution networks installations in the electrical landscape: overhead and underground networks,. Each one of them has its benefits and disadvantages. Let’s focus on the underground lines.

Buried technology is often used in big cities with high population density. Indeed, the installation cost as well as the maintenance are expensive, so the promiscuity of the premises makes it worthy because the distances to be covered by the distribution networks are quite small. In addition, in city centers, the needs are significant and the underground cables, with their larger cross-sections, which can go up to 300mm², make it possible to meet this growing need for energy.

This solution is more aesthetic and also more secure: no risk of a line being damaged by the wind or by a falling tree. Even if the underground is freed from a few constraints existing with overhead lines, the implementation and maintenance represent the critical points of these installations. In fact, working on buried networks involve road works and the use of civil engineering machinery. Maintenance is therefore more complex, less rapid and requires fitters well trained to this technology…

 

Several installation levels for the underground operations

Various types of architecture :

  1. The totally buried technology which the fitter cannot access from the ground without digging because all components are buried.
  2. The half-buried technology is below the ground surface but within a pit. Conductors come from the ground but all connections remain accessible by the fitter without having to dig.
  3. And finally, emerging solutions are described as aboveground systems, conductors being buried but all connections remain accessible by the fitter without having to dig. There, the installation is located in a cabinet type shell.

Let’s discover their benefits and disadvantages.

 

Buried underground networks

Buried technologies will mainly be used for cables lines and underground tap connections, for installations which need infrequent operations.  The underground facilities are developed and installed to last 40 years. In the ground, the cables are protected from meteorological events, road accidents or even vandalism which can damage the installations. Any installation, on the other hand, which is totally buried will require a perfect sealing to prevent corrosion and short-circuiting effects.

If the mechanical protection is less important than for overhead lines, cables must be protected from severing especially during works. In order to prevent those incidents, protective plate, signage equipment are used by fitters.

 

The pit environment for half-buried technologies

As mentioned before, the disadvantage of buried networks remains the difficulty to access the lines for operation and maintenance. Thanks to a half-buried solution, the connection accessories used to realize  a tap connection, a junction, a protection device are placed in a pit. Therefore, the fitter will come and lift the lid from where he will easily change a faulty part, check the installation, create a cut on the network … These installations remain protected from unwanted manipulations because they are sealable. These environments are airtight, but the equipment placed inside must enable partial and temporary operation in water, an event that can occur after heavy rains and flooding. The main drawback is the small footprint of the space which can make the fitter’s work harder, especially in a squatting position, and can also create the risk of overheating.

This system is the good compromise because it is quite aesthetic, little subject to external deterioration where it is quick to intervene.

 

Emerging installations

The last category describes emerging technology. As its name suggests, the underground network is made to emerge from the ground to make connections, tap-off and other functions needed in a distribution network. The emerging solutions can also enable the link between the underground and overhead networks.

The benefit of this technology is above all the ease of maintenance. The fitter works at breast height. It also helps bypass the need for waterproofing required in underground. Here we find the same constraints as in the air, mechanical protection, UV resistance, resistance also to water penetration …

This solution fits into the urban landscape because the connections are stored in a shell, often a cabinet. The asset of underground networks of being hidden is therefore lost. Nevertheless, manufacturers work with utilities to provide aesthetic consistency in the shells used.

Ultimately, which technology to prefer on the network?

The choice in one technology or the other will lie in a trade-off on the part of the utility between the cost of the installation, the ease of intervention on the network, the desired functions, the consistency and the aestheticism of the installations… The underground installations offer a wide panel of options; where to place the fuse protections? How to make the underground junctions? Create an disconnection point by emerging the network? … As an expert in the field and thanks to its experience acquired on networks worldwide, MICHAUD supports you in the choice of your installations and the definition of your system.

 

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