Abstract
The conventional electric quench-detecting system of AC superconducting coil is vulnerable to the electromagnetic noise, so the systems have problems in quench-detecting sensitivity and reliability. Recently the systems combined with physically different methods for the purpose of increasing reliability were reported. If oxide superconductor in R & D are applied to current lead of superconducting coil, such type of current lead is supposedly composed of a simple bulk structure. It is potentially brittle and catastrophic under thermal shock by rapid temperature rise when quenching occurs. Moreover, because of thermal insulation, the fully stabilized design is not applied to the current lead. So, higher speed quench-detecting system is required. This paper presents the development of high speed quench-detecting system using personal computer and digital signal processor (DSP). The DSP is a processor to realize the fast calculation of addition (subtraction) and multiplication by pipe line processing. Basically the four-terminal method is used. The quench-detecting is performed by evaluation of the mutual correlation factor for current through the current lead and its potential difference. In the superconductive state the voltage is measured which leads by π/2 radians to the alternative current, then the factors is ideally equal to zero. On the other hand, in the quenched state the voltage is deformed due to superposing the resistive voltage component emerged, the evaluated factor results in having some nonzero values, and thus the quenching can be detected. In this paper, it is indicated that the calculation of the factor can be processed for every one cycle of current and voltage, and the quenching recognition is performed at least within 17ms for current of 60Hz. This value would be reasonable for the protection of the coil system from catastrophy. It was also discussed that the method using the mutual correlation factor can well recognize the quenching state, even if the higher harmonics due to the electromagnetic noise were included in the measured voltage.
