New measurement technology optimises the manufacture of high voltage cablesFor several years selected parts of the traditional overhead line mains for electricity provision have been replaced by cables which are located on ground. There are several reasons for this, for example, that a cable network is more robust against storms during the autumn and winter, but also that there is a desire to avoid overhead line mains in urban settlements.
ABB AB, High Voltage Cables is one of the world's leading manufacturers of electrical power cables for high voltage and copper and aluminium are used as electrical conductors. Given that the conductor in a cable may typically be 5 cm in diameter and several kilometres long and raw material costs are high, it is advantageous to optimise the technical construction of the conductor in order to be capable of saving material, naturally by retaining the electrical properties.
By means of SP's self-developed coaxial current shunts as a basis, a reference method has been prepared for determining current displacement in electrical power cables. The method is of great financial significance for design and production as it optimises the material usage, in this case copper, in relation to the cable's electrical "losses".
It is essential to take current displacement into account during the manufacture of electrical power cables which transmit alternating current. Current displacement means that the current runs along the surface of a conductor and not homogenously in the conductor, which increases the resistance. Therefore, a cable is constructed with many strands which are assembled in a complex manner in order to reduce current displacement and thereby minimise losses.
Under the authority of ABB, we have used our self-developed digital samplings wattmeter and coaxial current shunts as a basis and prepared a reference method for determining current displacement. In order to verify our measurement method we have also designed and constructed a "cable" with theoretically quantifiable losses.
The project has turned out very well and in June 2011 ABB and SP together presented the work at an international cable conference. By means of the international publication, ABB shows that it is in the technology front of the development of high voltage cables and it is expected that the publication will put pressure on the competitors to illustrate the amount of current displacement in their cables.
Until now all measurements have been conducted at SP but they will be "moved" to ABB, both the hardware but also in terms of competence in order to thereby provide the possibility of more production-oriented measurements at the factory in Karlskrona.