EuroWire January 2023

Technical Article

Connection and joints One other important factor in the selection of conductive materials is the connections and joints. There are four main mechanisms affecting electrical connections. These are: 1 – Oxidation

Conclusion Based on what was mentioned above, there is no abstract answer to the question of which is better, copper or aluminium in electric power cables. The answer to this question is relative and varies from person to person and from one application to another, but generally: if you are looking for acceptable technical characteristics in addition to a lower cost, then aluminium will be your best choice; if you are looking for high technical properties despite the cost, copper will be your best choice. A cost–benefit analysis (CBA) – a systematic approach to estimating the strengths and weaknesses of alternatives used to determine options – provides the best approach to achieving benefits while preserving savings.

2 – Galvanic effect 3 – Cold flow/creep 4 – Thermal expansion

Oxidation Oxide, which causes reduction in the metal-to-metal contact or increased contact resistance at the connection point, consists of sulphide or inorganic films. This effect may cause the contact surface to warm up and increase the temperature at the connection point, resulting in malfunction. In contrast to aluminium, copper joints rarely overheat and do not require any surface preparation or usage of antioxidant compounds. Galvanic effect When aluminium and copper come into contact with each other, aluminium can physically lose its structural property by electrolytic effect. The connection point is both mechanically and electrically deteriorated due to a reduction of the contact surface or corrosion. For this reason, an aluminium conductor used in conjunction with equipment and accessories such as contact seals, bimetallic termination or special equipment needs implementation of a series of insertion techniques. Cold flow/creep Pressure is applied to create a good connection structure and to ensure high contact of the conductors. This operation may cause the metal to “flow”, therefore to deform. While this effect is mostly seen in aluminium conductors, the effect for a copper conductor, which is more rigid, is so much less that it is not significant. When the conductor is under stress, the deformation of metal – depending on the level, duration and temperature of the stress – is called “creep”. Both cold flow and creep lead to decreased contact pressure, increased joint resistance and, thus, overheating. Aluminium creeps more than copper, faster and at lower temperatures. Thermal expansion While no relaxation is observed at the connection points made with copper-copper, brass-copper or cable lugs, thermal expansion of aluminium conductors can cause loosening over time. Increased contact resistance increases the overheating and arc potential, thus increasing the risk of fire. Joint connections with copper are stronger, more resistant to corrosion, and more reliable and durable (because they are less sensitive to cold flow and thermal effects) than aluminium joint connections.

References 1 Power Cables and Their Applications, “Siemens” by Lothar Heinhold/Reimer Stubbe 2 Electric Cables Handbook: BICC Cables by GF Moore 3 Technical Tips – “Aluminum cables or copper cables?” – Türk Prysmian Kablo ve Sistemleri AŞ

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January 2023