Electrical Resistivity of a High-Tc Superconductor for Electric Current Higher Than Ic
The electrical resistivity of a high-Tc superconductor for I > I c is not clarified until now as a function of electric current through the conductor, I, and temperature of the conductor, T, because T varies with I due to joule heating. An estimation method of the electrical resistvity based on non-boiling heat transfer coefficients for exponentially increased heat inputs to the high-Tc test sample in LN2 was developed: exponential heat inputs, Q = Q 0 e t/T, with the periods, T, ranging from 10 ms to 10 s were given to a silver sheathed BiPbSrCaCuO tape in LN2, and electrical current I through the sheathed tape and the terminal voltage V between potential taps on the tape during the transient heating were measured. An empirical equation for the electrical resistance U. of the sheathed tape was obtained as a function of I and T: two constants in the equation were fitted iteratively so that the value of T at each time obtained from the measured values of I and V at the time by using the equation of R may agree with the theoret ical solution of nonboiling heat transfer for the exponential period. The distribution ratio of the electric current through the superconductor and the Ag sheath, I N /I, and the flow resistivity of the superconductor itself were estimated by using this method.
KeywordsElectrical Resistivity Distribution Ratio Natural Convection Heat Transfer Flow Resistivity Transient Heat Transfer
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