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Figure 1: Steel lattice HV towers used to transmit electricity (John 2023)
Another component of an HV tower is the tower footing earth electrode. This earthing is crucial for the protection of plant equipment from large fault currents. How the footing resistance does this is by “providing a low impedance path” from structures to a mass of earth where large fault currents are dissipated (Kose and Hamer 2003; Naidoo 2019). The tower footing electrodes are normally made of copper. Copper attracts theft due to its economic appeal and is a high-risk material. The combination of this appeal, and the fact that the electrodes are at ground level, and exposed before entering the earth, makes the tower footing electrodes a desirable and easy target for criminals. The electrodes can also degrade due to age or corrosion. If the electrode is degraded or stolen, field equipment can be damaged until the degraded/stolen electrode is discovered by in-person inspections.
Several methods have been used by power utilities to mitigate the theft of steel members. A common way in which steel members were stolen was through loosening the bolts to remove individual steel members. To mitigate for this, specialised swage bolts were used to secure the members in place. This was successful to an extent, because a specialised swaging tool was needed to remove the bolts (Morrison 2012). However, criminals resorted to simply using an angle grinder to cut the steel members free. Eskom tried branding steel members with ‘ESKOM’ – which would make it easier to trace the stolen members (Ruffini 2013). Again, this method deterred criminals only slightly as they could just melt the steel members, which
neutralises the evidence. Regular patrols and inspections for the tower footing resistance and HV towers are conducted annually; however, criminals can still act in between patrols. Increasing the frequency of inspections will be difficult and expensive to enforce due to the number of HV towers and due to some of them being in areas with limited accessibility. The estimated length of HV transmission lines is about 28,000 km and the average span between towers is “400 m” (ESI 2021). This typically means that in a span length of 1.2 km, there are probably 3 HV towers. This means conducting line patrols for every tower is not practical or economically feasible. One system that is being explored is the use of artificial intelligence- enabled drones to conduct more frequent inspections; however, this proposal is still in its infancy. A method that can be used to mitigate steel member theft is to use steel monopoles to transmit the high power. These towers do not have any steel members on them as the tower design is a single pole instead of the lattice design. These monopoles will not be attractive to criminals in terms of profit. It must be noted that steel monopoles can only be used in relatively flat areas (UETCL 2024).
Tower footing electrodes can be protected from theft by manufacturing the electrodes from steel with copper plating. This has proven to reduce the amount of theft. It was noted by Eskom that on several occasions “cut marks have been observed, but the conductor is not taken as thieves realise this is not the copper they are seeking”. Other methods that can be used are burying the footing
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