Electrical measurements on samples of superconducting cables are usually performed in order to determine the critical current $I_c$ and the n-value, assuming that the voltage U at the transition from the superconducting to the normal state follows the power law, U\sim($I/I_c$)$^n$. An accurate measurement of $I_c$ and n demands, first of all, good control of temperature and field, and precise measurement of current and voltage. The critical current and n-value of a cable are influenced by the self-field of the cable, an effect that has to be known in order to compare the electrical characteristics of the cable with those of the strands from which it is made. The effect of the self-field is dealt with taking into account the orientation and magnitude of the applied field and the n-value of the strands. An important source of inaccuracy is related to the distribution of the currents among the strands. Non-uniform distributions, mainly caused by non-equal resistances of the connections between the strands of the cable and the current leads, can easily result in a misinterpretation of the measured critical current and n-value by 5% and 50% respectively. In this paper this effect is explained in detail, taking also into account the influence of the current ramp-rate (during a voltage-current measurement), the sample length, the contact resistance between the strands and the placement of the voltage taps.
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机译：通常，对超导电缆的样本进行电测量，以确定临界电流$ I_c $和n值，假设从超导状态转换到正常状态的电压U遵循幂定律U \ sim（ $ I / I_c $）$ ^ n $。要精确测量$ I_c $和n，首先需要对温度和场进行良好的控制，并精确测量电流和电压。电缆的临界电流和n值会受到电缆自身电场的影响，为了将电缆的电气特性与制成电缆的电气特性进行比较，必须知道这种效应。考虑到施加场的方向和大小以及钢绞线的n值来处理自场的影响。误差的重要来源与各股之间的电流分布有关。不均匀的分布主要是由电缆绞线和电流引线之间的连接电阻不相等引起的，很容易导致分别将测量的临界电流和n值误解5％和50％。在本文中，还考虑了电流斜率（在电压-电流测量期间），采样长度，线股之间的接触电阻和电压抽头位置的影响，详细说明了这种影响。
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