Cable Ducts

INFILL OF HIGH VOLATAGE CABLE DUCTS WITH A LOW THERMAL RESISTIVITY MATERIAL.

The UK Government is perusing ways for greener energy to supply electricity.

Wind-farms are one of the solutions, with large off-shore turbines creating electricity to feed the ever increasing demands for households and industry, as well as nuclear power stations.

The power generated from these turbines is transported to landfall via large power cables. When building these wind-farms the cables are laid along the sea bed from the wind turbine to landfall. The cables, are then pulled through a duct up to a kilometre at sea to avoid any damage to the cable from collisions with shipping vessels or fishing boats. When the cables are pulled through the duct it ends up some distance in land (+/- 200 meters from the sea as shown in the below picture)

Picture shows cable duct with injection line to infill with material

Picture shows equipment to manufacture material with the sea in the back ground

The cable duct is located some distance in land and the power generated from the wind farm via the cables is transferred to the grid. In turn this will cause the cable to generate heat. If excessive heat is produced this will reduce the cables lifespan and increase wire resistance.

When electricity cables are strung on pylons the air dissipates the heat very quickly so there is no damage to the cables or loss of power. However, when a cable has to be laid on the ground and pulled through a duct, once it becomes live the heat from the cable quickly heats up the surrounding area. Therefore, a liquid grout needs to be injected into the duct prior to becoming live.

The objective to infill cable ducts holding electricity cable is to avoid the build-up of heat within the duct.
Depending upon the diameter of the cable and the amperage rating together with the duct diameter, BMSL can supply and install material that will give the following values.

Mix Thermal Conductivity Thermal Resistivity
1.0 1.0 W/m.K 1.0 m.K/W
1.3 1.3 W/m.K 0.8 m.K/W
1.5 1.5 W/m.K 0.7 m.K/W
2.0 2.0 W/m.K 0.5 m.K/W
2.5 2.5 W/m.K 0.4 m.K/W

The mixes in the table would be advised by the client or cable manufacture or contractor as to the required TC/TR value for each project.

Another advantage with using our material is it does not contain any cement. It is a special graphite/bentonite blend that does not fully set. Therefore, if the cable needs to be removed for any reason in the future, this will still be possible. The material hardens to the consistency of a cheese cake when the cable is moved the grout reverts back to a liquid making it easy to remove the cable.

Some of the advantages of using our special grouts.
1) High flowability over long distances (1000 + linear meters)
2) No water/product separation
3) Excellent TC & TR values from 1.0 – 0.4 m.K/W

If you require any further information on cable duct infill’s please contact us.