Commissioning and first operational experience with the new thyristor converter Group 7 of ASDEX Upgrade

Abstract

Due to the continuously expanding experimental program of ASDEX Upgrade (AUG), the high current converters came to their limits. At the same time, the risk of failure increased because of the equipment aging. In order to reduce this risk and to extend the area of operation, a new thyristor converter called “Group 7″, equipped with a recently developed digital control system, was installed. While the design was already published on SOFT 2018, this paper will describe in detail the commissioning results and the first operational experience of the new thyristor converter. The manufacturing and on site installation of Group 7 started in 2018 and was finished in spring 2021 by the delivery of the transformers. In parallel to the construction process the main components were type-tested. One of four converter modules was extensively verified during the factory acceptance tests. In order to be able to test the digital control system independently of the construction of the power converter, a scale model was built. All functions of the control system were tested on it. It was also useful to investigate the problems arising during commissioning and to verify firmware fixes. After finishing the site installation work, the converter was proved in all possible configurations on a test coil. These tests were performed in local and remote control. Attention was also paid to the effect of power factor improvement by neutral-point vs. regular bridge (B6) thyristor configuration. For this reason, all tests were performed with and without operation of the neutral-point thyristors. The last step was to operate the converter on the magnet coils of AUG. In an intensive test program over a period of six month, all poloidal field and OH coils of AUG were operated with the new converter in the required operation mode.