Analysis and countermeasure for a problem of abnormal voltage generation in a SMES magnet

We have experienced a problem due to the abnormally high voltagethat damaged one of six coils in a 1kWh/1MW SMES ( Superconducting Magnetic Energy Storage). The damaged coil has already been replaced and the whole system is now in operation without any problem. We will report here the analysis and discussion of the problem of high voltagegeneration based upon the recorded current wave form. It was estimated that the problem had originated by an accidental grounding of a thin potential lead wire connected to a point of interconnection between two coils, which was then followed by a disconnectionof the short-circuit by wire melting. This disconnectionof the wire bearing current caused a generation of very high voltageand the resulting damage of the coil. Theoretical considerations with simulated calculations are made to confirm the above estimation quantitatively. A countermeasure for this sort of problem is also presented.