High voltage power cables for bulk AC power transport use the Milliken conductor design from a certain cross section up to decrease transmission losses. It is not possible to reliably assess their AC losses by simulation or other calculation methods in advance, as the performance of this complex design strongly depends on manufacturing processes and quality. The exact knowledge of the AC resistance is important, because it is a critical design parameter for the thermal dimensioning of the cable and whole cable systems. Therefore, it is necessary to accurately determine the AC losses by measurement using the electrical or the calorimetric method. This work focuses on the electrical method solely, as it can be performed much faster with less logistical effort. The goal is to have a measurement setup, where the measured losses are as close as possible to the true losses. The true losses result in conductor heating, which limits the transmission power. They are also called Joule losses. Theoretical calculations, FEM simulations in Comsol Multiphysics and measurements have been used in combination to evaluate different, possible influences in AC resistance measurements. After the problem definition and the presentation of the methodology, past advances and concepts focusing on AC resistance determination were shown. Then, after the basics were made clear to the reader, the measurement circuit was defined and different error sources in measurement setups were evaluated. These included the influence of the sheath and return conductor position upon true and measured losses, the influence of current homogenization and placement of voltage tap-offs. A recommendation for the preparation, setup and measurement procedure was given. At the end, multiple Milliken conductors were measured using the proposed method and compared to the IEC standard. It was shown that the electrical measurement method is able to measure the true AC losses of complex conductors consisting of insulated wires. One important requirement is that the voltage pick-up loop is large enough to capture enough complex magnetic field originating from the conductor under test. On the other side, complex magnetic fields caused by eddy currents in adjacent conductors should not be captured by the pick-up loop as they also affect the measured losses. Using 2 equally spaced return conductors in the same plane as the conductor under test and the average of at least 4 evenly distributed voltage pick-up loops located at the surface of the insulation of the cable, will deliver results of sufficient accuracy. The findings of this thesis indicate that great care must be taken for multiple aspects in the AC resistance measurement of complex conductors. Engineers performing AC resistance measurements have to be aware of error sources, specifically the interplay between conductor positions and apparent losses. The electrical measurement method needs to be thoroughly prepared, especially regarding the contacting of current path and voltage tap-offs. Nevertheless,the effort concerning time and logistics is still significantly smaller compared to a calorimetric measurement.
Alternating current loss measurement of power cable conductors with large cross sections using electrical methods
Die Messung von Wechselstromverlusten von Hochspannungskabeln mit großen Querschnitten unter Verwendung der elektrischen Methode
2018
Sonstige
Elektronische Ressource
Englisch
DDC: | 629 |
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