It is imperative that the method for evaluating and expressing uncertainty in measurement should be uniform among scientists and engineers so that measurements performed in different scientific and technological fields can be easily compared. This article attempts to familiarize scientists and engineers with general concepts of uncertainty in measurement that are based on the ISO Guide of Uncertainty in Measurement (GUM). This uncertainty consists of several components that may be grouped into two categories, A and B. These categories do not correspond simply to “random” and “systematic” uncertainties that have been used previously. The article explains what category A is and what category B is and how to classify the several components into theses categories. The importance of the uncertainty budget table is also emphasized.
Quench propagation velocity is one of the most important parameters for the quench protection of superconducting magnets. We examined the relations between the current redistribution and the quench propagation velocity in a Rutherford cable made of noninsulated strands. Measurements were performed in the cables with three contact conditions between strands, and it was found that the quench propagation velocity and the current redistribution depended on the contact conditions between strands. A numerical simulation of current redistribution using a simple model was performed. We made comparisons between the test and the numerical results, and there was good agreement. We analyzed the numerical results in detail and found that the current redistribution caused by the magnetic field distribution in the cable cross-section around the boundary of the normal zone, normal front, enhanced the quench propagation velocity.
Thermal runaway properties of Ag/Bi-2212 tape cooled by a cryocooler have been studied experimentally under the condition of magnetic fields up to 15T at 4K. To investigate the stability of the tape, Joule heating and a sample temperature were measured as a function of time at a fixed operating current. As a result, if cooling capacities are higher than Joule heating, it is found that thermal runaway current, Itr, is higher than critical current, Ic, which is defined by 1μV/cm. Furthermore, MRE (Minimum Runaway Energy) was measured as a function of operating current ratio, Iop/Itr, and the magnetic fields. The MRE decreased with increasing magnetic field in the same operating current ratio.
We present a new type of active-maglev system composed of high-temperature superconducting bulk and multiple electromagnets. One useful feature of the active-maglev system is that levitation height is adjustable by varying operating current in electromagnets. Maximum levitation height in stable levitation, however, is restricted by magnetic field distribution generated by the electromagnet. To improve the levitation height, we designed and constructed an active-maglev system with two electromagnets instead of using a larger single electromagnet. The levitation height, as well as stability, was remarkably improved by adjusting the operating current of each electromagnet individually. We also analyzed the electromagnetic phenomena in high-temperature superconducting bulk by the finite element method. The experimental and computed results imply that much higher levitation height could be realized by using multiple electromagnets and adjusting the operating currents.
A superconducting fault current limiter (FCL) is one of the most useful devices to stabilize the electric power network system. And many types of superconducting FCLs have been proposed and developed. For the superconducting FCL, a normal phase transition phenomenon is the most important and fundamental function to increase FCL impedance, but it thermally shocks the device and brings excessive heat load to the refrigerator. The diode-bridge type of FCL is known as a superconducting FCL that does not require a direct normal phase transition in the function; the excessive current may actually trigger the current quench of the superconducting magnet. Therefore the elaborating technology against the normal phase transition must always be considered for any type of superconducting FCL. To solve the phase transition problem of the superconducting FCL, we propose a nonquench type of superconducting FCL in this paper. The proposed FCL belongs to the LC resonance-type FCL, and superconducting magnet current in the FCL can operate under a limited value by an arrester, which makes nonquench operation possible. This paper mainly describes numerical analysis and shows the validity of the proposed FCL by means of a small experiment.