Protection of LHD coils by intelligent observation of voltage signals

LHD is a typical large-scale superconducting coil system with very large magnetic stored energy. So, its protection at any operational condition is very important. In order to protect the large superconducting coils, a careful observation of voltage signal is essential. However, in general, the observed voltage signals have considerably large electromagnetic noises. Therefore, the authors cancelled the noise voltages by subtraction of a voltage of an adjacent coil from that of the target coil. Besides, the authors propose an intelligent data processing method using both integration and differentiation technique of the voltage signal. These techniques are applied for the LHD data. The obtained result well explains the normal-zone expansion phenomenon at LHD obtained in October 1998.