The importance of high-power relays used to interrupt dc current has been significantly growing recently. In their arc chambers filled with nitrogen or its mixtures, bridge-type contacts with permanent magnets are major measures widely used for arc extinguish. Arc dwelling for a short duration after arc ignition, until its voltage increases rapidly, plays a crucial role in contact erosion. In this paper, arc dwelling time in a nitrogen environment during the entire bridge-type contacts interruption process of a resistive dc circuit is studied both experimentally and numerically. A multiphysics model coupled with the fluid flow, the temperature, the current density, as well as the E- and M-fields was built based on the magnetohydrodynamics theory for the arc chamber. The model was solved in COMSOL. The external resistive electric circuit was connected to the model, and the electric field in the arc was solved by adopting a floating potential. The detailed arc dwelling process is presented and preliminarily discussed according to the calculated temperature and current density distribution sequences. The calculated arc voltage shows good agreement with experimental results. Furthermore, the influence mechanism of breaking velocity on arc dwelling is analyzed by arc voltage. In this sense, the arc dwelling time could be shortened by increasing the breaking velocity within the reasonable extent.

In recent years, with the development of ship electric propulsion system, High Temperature Superconducting (HTS) motors have gained attention as a promising potential resolution due to their high-power density and the progression of cryogenic refrigeration technology. We present an electromagnetic characteristics numerical analysis of 40 MW, 120 rpm, HTS synchronous motor which is a semi-superconducting motor: in fact, it has a superconducting rotor composed of YBCO material and a conventional stator. Combining electric resistivity variation of rotor copper shielding sleeve in low temperature environment and YBCO coil critical current, the electromagnetic behavior of the 40 MW HTS synchronous motor is analyzed with non-ferromagnetic stator support structure. To assess the effects of varying stator winding currents and thickness on eddy current losses of the copper shielding sleeve, calculations were done, and a preliminary discussion was initiated. This study has certain reference significance for electromagnetic design and optimization of multi-ten MW HTS motors, especially used in ship electric propulsion system.

Compared with conventional electrical motors, HTS motors due to the higher electromagnetic loading have the advantages of high power density. With the continuous development of HTS and refrigeration technology, HTS motor is gradually applied in the propulsion system of ships, and has broad application prospects. In this paper, firstly we have built a electromagnetic model for high power density HTS ship propulsion motor based on the ANSYS software according to the design, the ReBCO rotor coils rated working current is set to 310 A by reserving a safety margin of 40% when the airgap flux density is 2.3 T, which is obtained by optimized stepped geometry magnet. It has been studied the performances of temperature varying and mechanical strength of HTS rotor through numerical simulation. Finally, the magnetic coil prototype is fabricated to validate the correctness of the proposed analysis and design methods.

Accurately calculating AC loss in high-temperature superconducting tapes is crucial for the operational cost and stability of power equipment, such as superconducting motors. The model of superconducting tapes can be simplified by considering the dimensions of layer thickness and resistivity. The effectiveness of this simplified method can be verified by analyzing the external magnetic field amplitude, frequency, and loading rates, and studying the variation law of AC loss. The impact of temperature rise on AC loss can be considered by introducing thermal coupling module. It has demonstrated that this simplified method is both reasonable and effective. It is vital to consider the influence of temperature rise while calculating the AC loss of superconducting tapes, particularly under high load rates, high amplitude and high frequency.