Sudden Discharging Tests and Overcurrent Tests of a 3T HTS Model Magnet for MRI Systems Equipped With Electrically Conductive Epoxy Resin
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A 3 T HTS MRI model magnet equipped with conductive epoxy resin for quench protection was designed and fabricated in 2021 and the REBCO multicoil generated 3 T with 143 A stably with no abnormal voltages. In this coil, the electrically conductive epoxy resin is attached to the edge of the winding as a bypass circuit between turns so that the excessive current can flow across turns in the radial direction to suppress local heat generation automatically. However, when the voltage of the coil rises as a start point in a quench protection process, the DC power supply is shut down by a quench detector and the magnet is suddenly discharged. Then, part of the magnetic stored energy is consumed in the coil and the coil temperature increases, which suggests the load factor increases during the sudden discharging operation. In this study, the sudden discharging tests were performed, and the behavior of the coil voltages and temperatures was evaluated at 30 K and 40 K using the middle-scale REBCO coil that had large inductance and high stored energy (3 T, 91 H, 1 MJ). After that, the overcurrent tests were performed for the verification of the quench protection at 50 K. The coil temperature reached 72 K at maximum, however, thermal runaway was avoided and the REBCO coil was protected.Keywords:
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Traditional overcurrent protection settings are calculated in the worst condition and the settings will not change with power system operation mode.For the problems in the traditional overcurrent protection,the settings were not optimal in some conditions.Based on the theory analysis of traditional overcurrent protection disadvantage, this paper presents one new self - adapting overcurrent protection method to adjust the settings according to the different condition and fault and directional element is equipped in some overcurrent protection.A better adaptive overcurrent protection system is established with multi - agent system(MAS).With the merits of MAS,the adaptive over-current system can adapt the change of power system better.
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The mechanism of the overcurrent and overvoltage protection module—YD-CLP200M under different protecting modes such as overvoltage,positive surge overcurrent and negative surge overcurrent is analyzed,and the internal equivalent circuits corresponding to structural parameters of the device are given.According to different structural parameters,the I-V characteristics of the switching-on voltage and the positive surge switching-on current are simulated by using MEDICI device simulation tool,whose results indicate the dominating factors that affect these DC parameters,from which we can get adjusting method on structural parameters to optimize the device's DC characteristics.
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