An Automatic Compensation Method for Measuring the AC loss of a Superconducting Coil

For measuring the ac loss of a superconducting coil by electrometric method, an additional compensating coil is required to cancel out the inductive voltage produced in the superconducting coil. There are disadvantages such as low mechanical control precision, narrow compensation range, and voltage with harmonic components when using compensating coils. In order to measure the ac loss of a superconducting coil easier, this paper proposes an automatic compensation method. In this method, a compensating voltage is automatically produced to replace the compensating coil; the amplitude and the phase shift are controlled with numerical process. Key technologies are described here in detail such as the amplitude control and the phase shift of the compensating voltage. Also, a usable hardware is constructed and practical measurements are realized with superconducting coils on the self-field condition. Comparing the results with that by a compensation coil and finite element simulation shows that the proposed method can measure the ac loss of a superconducting coil easier and with high degree of automation, as well as high stability and low harmonics.