Computer program for the calculation of short-circuit temperature rise on optical ground wires

Optical ground wires (OPGW) are increasingly being used on overhead transmission lines throughout the world. OPGW conductors protect the power line against lightning or short-circuit and provide communication through optical fibres embedded inside the conductor. In case of conventional ground wire, the permissible instantaneous temperature is limited by the highest allowable loss of tensile strength of metallic materials caused by annealing and bird-caging. Since OPGW conductors are expected to give protection to the embedded optical fibre, they shall meet a further requirement; i.e. the temperature of the conductor shall not rise in such extent that it may cause degradation in the parameters of the optical fibre. The highest temperature that the conductor may reach during and after short-circuit depends on the conductor design. Accurate and reliable information on the short-circuit temperature rise is a vital question for the design work, but existing calculation methods cannot be used for complex OPGW conductors. At VEIKI-VNL, a computer program was developed for the simulation of short-circuit test on OPGW conductors. The program is able to calculate the temperature of each component of the conductor. This paper describes the short-circuit behaviour of typical OPGW conductors, the drawbacks and limitations of the traditional calculation and the theory of the calculation method used in the new program.