Feasibility Study of a High Voltage In-Service-Tests on the Superconducting Magnet System of Wendelstein 7-X

During the energizing and de-energizing process of the Wendelstein 7-X magnet system, the forces induced in the superconducting coils could lead to stresses in the insulation of the coils, the interconnecting bus system, the current leads and the mechanical support structure. Such stress could cause a ground fault that would not be detected during normal operation. In normal condition the voltage across a coil group is halved by a middle point grounding system. If a ground fault is present during a fast discharge, the coil group could be stressed with the full voltage of up to 4 kV which could endanger the high voltage integrity of the whole superconducting magnet system. To prevent such undesirable occasions, the insulation of the superconducting magnet system shall be monitored by a high voltage In-Service-Test. That means that a test voltage shall be applied during the operation of the magnets. Therefore, it is planned to temporarily lift the middle point of the grounding system by a high voltage source of 2.5 kV and to measure the leak current. To evaluate the feasibility of such a system, a simulation model of one coil group has been created in Simplorer. Considering detailed parameters of the coil group, the model shall support the evaluation of how the high voltage influences the superconducting magnet system and shall determine the leak currents with and without certain damages in the insulation. The paper describes the Simplorer model with its different simulation scenarios and summarizes the results and findings.