Optimization of High Voltage Cable Dimension in Scania Electric Vehicle’s Systems

Sammanfattning: With the increasing demand for electrified vehicles, the demand for electrical components, including cables, is rising too. Thus, it is important to develop a method to optimize the cable sizing to ensure the cable is technically robust and economically efficient. The aim of this project is to study and evaluate different cables’ designs to find the optimum dimension for “high voltage” class (automotive voltage class B) cables in the electrical vehicle system. Three important technical aspects in evaluating the optimum cross-section area (CSA) are the ampacity of the cable, short-circuit withstand capability and voltage drop.In this project, the ampacity of a cable placed in air is calculated by the analytical method based on IEC 60287 and by a finite-element simulation. These results are verified against direct measurements using a dc source and load. In DC calculation, the similarity of all three methods is high, within 96%. The formation of the cable also affects the ampacity of the cable. For DC currents, the vertical formation has a higher ampacity than the horizontal formation, by almost 2%. For AC currents, the trefoil formation has a higher ampacity than the horizontal and vertical formation, by around 6-9%.Calculations of short circuit withstand capability and voltage drop were performed to ensure cable performance. The larger CSA corresponds to both higher short circuit capability and lower voltage drop. In a short circuit, a duration around 0.5 s is critical since there is a significant difference between short circuit withstand capability before and after this. Voltage drop calculation is performed to ensure that the combination of CSA and length does not exceed 3% voltage drop at the load end side of the circuit. The Voltage drop is not found to be an important factor to consider. Based on those three factors, the optimization process is described with a flowchart.