Temperature Rise of Optical Fiber Ground Wires Subjected to Short Duration-High Current Transients

A thermal model capable of predicting the local temperature history in an optical fiber ground wire (OFGW) when it is subjected to a short duration, high-current transient is discussed. The model is used to predict the temperature rise that can occur from typical lightning strikes and from contact with an energized phase conductor. The model is capable of predicting the temperature rise at all locations in a three layer composite OFGW consisting of materials with vastly difficult thermal and electric properties. The composite design results in alternating regions of high and low heat generation. This uneven heating results in temperatures that can significantly exceed the temperature predicted by the usually conservative adiabatic thermal model. The temperatures predicted by the thermal model are verified in a series of laboratory tests in which the temperature rise of ground wires are measured with thermocouples. A single thermal design parameter is introduced as a means of evaluating those design factors which will influence the temperature rise of an OFGW. The thermal model is used to show that small changes in the design parameter can have a large influence on the temperature rise of a ground wire when subjected to a short duration-high current overload.