Partial discharges measurements performed on cryogenic joints [superconducting magnetic energy storage]

Superconducting magnetic energy storage (SMES) is based on a superconductive coil. The current leads of the considered SMES, operating between room and liquid helium temperature, consist of a resistive and a high temperature superconducting (HTS) section. In this work, the problems concerning the insulating system of the resistive section were investigated. These problems affect the copper wire insulating system and the aluminum nitride sheets interposed between two copper electrodes. A diagnostic tool, based on partial discharge activity, has been considered to obtain information about the insulating system and the AlN sheets status. Because the whole insulating system of the resistive current lead was designed in order to guarantee 5 years of normal operation, accelerated electrical ageing tests were performed, considering a more severe stress than the actual one, applying a sinusoidal 50 Hz waveform; during the electrical ageing tests, the signals relevant to partial discharges were acquired. The obtained results are presented and discussed.