| dc.description.abstract | Nowadays, the power companies show interest in maximizing the usage of cables due to constantly increasing energy demand and inconsistent power generation from the growing renewable energy resources, thus achieve optimal economy and reduce environmental impact.
The ampacity of the cable is limited to the maximum thermal capacity of the conductor that is dependent on the heat generated by ohmic losses in the metallic layers of the cable. . Overloading the cable can overheat the insulation which accelerates its aging and thus reduces the successful service life of the cable and the stability of the transmission network operation.
Therefore, it is important to study the rise of conductor temperature in other words thermal rating. As the static thermal rating is determined using the predicted worst-case conditions, the current carrying capacity of the cable can be improved by considering the transient thermal rating determined using the real-time measurements of current, temperature of cable surface and external environment conditions
The aim of this thesis is to analyze the transient temperature response of power cables to facilitate dynamic current rating. A literature review is conducted to provide an overview of the application of DTR followed by the inclusion of the theoretical background for the proposed approach of estimating the cable conductor temperature. Further, a calculative methodology is mentioned that describes the analytical method suggested based on the IEC standards for single-core and three-core cables. This method describes the appropriate thermal model which is used to calculate the conductor and screen temperature. The behaviour of transient temperature variation is investigated when varying current loads are applied to the power cables lifted from the floor (on air), placed on the floor, located in ducts/culvert and directly buried in soil.
an experimental methodology is presented that aims at measuring the transient temperature of the selected XLPE cables during varying current loads. A laboratory set up is established that measures the current applied and temperature at different layers of the chosen cables. This allows to compare and verify the measured results with the calculated results obtained from the analytical method
It is found that the thermal resistance of the three core cable is comparatively low which allows it to carry more current for a longer period before thermally stressed. The external thermal resistance of the cable is found to reduce with the higher cable surface temperature.
The results from the test with single-step current shows better estimated values compared to the measured results for rating temperature and for higher temperatures the deviation between simulated and measured temperature values is observed to increase with the temperature doubting the validity of the analytical approach for higher current.
The analytical method based on IEC standard are computed upon many assumptions. The three core cable model was simplified by considering equivalent single-core cable which seems to be an unreliable approach to successfully estimate the conductor temperature for DTR application. Therefore, it is concluded that the improvements on the calculative method is essential for an accurate estimation of temperature response. | |