Page 20 - Issue 2 2023

TECHNICAL

Substation and network earthing
Substation earthing systems and conductors are the most vulnerable to theft, as the
conductors are exposed. There is no convenient way to conceal transformer earth
conductors which are mostly copper. The earth conductor is not live, so it’s an easy
target for thieves. The theft of earth conductors at substations and other installations
poses serious risks to network protection and safety. Mechanical barriers are not
impenetrable, and the only solution is to use conductors which have virtually no resale
value. Earthing doesn’t require the same level of conductivity as pure copper since
only fault current is being carried. Less expensive and more theft-resistant bimetallic Figure 6: Copper coated steel conductor
conductors can be substituted with optimal results. Bimetallic conductors, specifically (Copperweld)
copper clad steel, can be substituted for pure copper in grounding applications with
very little risk of theft. Bimetallic conductors
Bimetallic conductors consist of a solid
Composite materials core of either aluminium or steel that
The use of composite materials for earthing is a solution that has been proven to be is concentrically clad in a thin layer of
effective. Composite material conductors combine copper with some other low value or copper via metallurgical bonding. For the
high strength material to produce a conductor which is difficult to remove and has low utility industry, most of the applications
scrap value, while meeting the conductivity requirements for earthing. involve copper-clad steel (CCS). CCS
A passive method to reduce copper cable theft involves disguising copper cable as is manufactured in three standard
steel guywire. Anti-theft wire may be made of many smaller tinned copper wires that conductivities: 20%, 30% and 40% of the
are bunched together, with a ring of steel strands that surround the copper. From the international annealed copper standard
exterior, the copper wire now looks like steel wire (Figure 4). The copper strands are (IACS), though for applications that require
tinned to improve corrosion resistance and are concealed by outer galvanized steel extra conductivity, it can be made with a
strands. The copper stranding increases conductivity and flexibility of the conductor. thicker layer of copper to carry up to 70%
This type of anti-theft cable maintains flexibility and conductivity while holding up of the current of pure copper. CCS can be
the disguise. Steel wires have little value when sold for scrap and these cables pass the made from three different grades of steel:
“magnet test” that many thieves use to look for coated copper conductors. Copper is not low carbon, high-strength and extra-high-
magnetic so if a magnet sticks to the cable thieves will typically assume the cable is not strength. While it has only 40% of the
copper. If it is discovered that there is copper inside the cable, it is difficult to separate conductivity of copper, CCS will meet the
the steel from the copper. needs of most earthing applications when
Composite steel and copper braid is another solution available as tapes or round the appropriate size is selected.
conductors. Anti-theft conductor tape and conductor is a composite stranded tape or
conductor made up of tinned copper wires and galvanised steel wires that are braided References
and interwoven to form the cable. The complex braided and interwoven wires of steel 1. Gavin Strelec, Eskom: Private interview
and copper make it very difficult to separate and are unattractive and uneconomical to 2. L Deamer: “Cutting down cable theft in South
copper thieves and scrap dealers. Africa”, Electronic specifier, 20 August 2020
3. A Munilal: “Anti-theft initiatives employed in
Copper clad steel rods cables”, African Utility Week, April 2016
Another solution is to use steel rods which are plated or clad with copper. The SANS 4. T Horton: “Bimetallic conductors: A
623 standard specifies earthing rods consisting of high tensile steel with a copper outer significant weapon in the war on copper
layer. These are not intended to be used as the main earthing system but have been theft”, Energize, October 2012
adapted as earthing conductors. The rods have 20% of the conductivity of equivalent
copper cross-sectional area. This is a solution that has proved to be extremely effective Send your comments to
in eradicating copper theft. 1 rogerl@nowmedia.co.za

(a) Braided Tape (b) stranded conductor (c) Braided conductor
Figure 4: Anti-theft cable (Nvent) Figure 5: Composite woven conductors (Kwenya)

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