Effect of partial insulation winding scheme on discharge characteristics of GdBCO coils

• Sudden discharge tests were performed on partially-insulated GdBCO pancake coils.
• The field decay time decreased with increasing the insulation-angle.
• The effect of the insulation-angle enhanced as the insulation-interval increased.
• Partially-insulated coils could be represented as a single RL circuit in parallel.
• The contact surface resistance model was modified by the current-bottleneck effect.

In this study, sudden discharge tests were performed on partially-insulated (PI) GdBCO coated conductor single-pancake coils to investigate the effects of a PI winding scheme on the discharge characteristics. Three sets of PI coils were constructed with insulation at 3 different intervals: every 2nd, 4th, and 8th turn. Each set included coils with 4 different insulation-angles: 90°, 180°, 270°, and 360°. Discharge delay of the PI coils was alleviated by increasing the insulation-interval or insulation-angle due to increased insulated area, which partially hinders radial current flow. The results of the sudden discharge test were in fairly good agreement with simulations of the PI coils using an equivalent circuit model consisting of a single RL circuit in parallel. The characteristic resistance of the PI coils was reasonably estimated through the numerical approach with contact surface resistance and compensation for the current-bottleneck effect, which enables the PI coils to be utilized in practical superconducting magnet applications.