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This paper reports empirical and numerical analyses on the electrical behavior of no-insulation (NI) coil. The spiral and radial current flows of NI coil in the case of the nominal operation and over-current condition are quantitatively identified using numerical analysis. Moreover, the origins of charging/discharging delays and magnetic field saturation are discussed in detail. Experimental results are also compared with the simulations to validate the numerical approach. [ABSTRACT FROM PUBLISHER]

This paper proposes a numerical approach to calculate the characteristic resistance (Rc) of partial-insulation (PI) and no-insulation (NI) high-temperature superconductor pancake coils with the nonuniform current path in such coils taken into consideration. Recently, an analytic approach has been proposed to estimate (R \rm c) of an NI coil, where the coil current is assumed to be “uniform” over the entire coil. This model, however, is not effective to explain the increase of (Rc) when a coil is modified from NI to PI. In this paper, we first introduce our numerical approach based on a finite element analysis. Then, the charging characteristics of selected PI and NI coils that we had previously reported are analyzed by the proposed approach. Reasonable agreement between the measured and calculated data validates the proposed approach to estimate (Rc) of a PI as well as an NI coil. [ABSTRACT FROM PUBLISHER]

Helical coil electromagnetic launchers (HEMLs) using rail-fed strategy, local excitation and single-turn commutation, solve the problem of synchronization control perfectly. Through the simulation, a novel helical coil launcher is designed using the basic HEML's structure. A D-shaped cross section armature is proposed to achieve the maximum projectile velocity. The energizing length of the driving coil, as well as, the armature position of the maximum force is determined. The maximum driving force on the armature increases with the increasing coil axial length and the armature acceleration reaches its maximum value when the ratio of axial to radial length of the coil is 1:2. The force distribution of the armature and driving coils is analyzed. [ABSTRACT FROM PUBLISHER]

This paper investigated quench initiation and propagation characteristics of grease insulation coils by conducting thermal-quench tests for two GdBCO single-pancake coils, namely a coil co-wound with silicon grease (termed as the SiG coil) and the other coil co-wound with Kapton tape (termed as the INS coil), as turn-to-turn insulation. The test results confirmed that the SiG coil exhibited better thermal and electrical stabilities when compared with the INS coil because the operating current could be bypassed in the radial direction through the turn-to-turn contacts when a local hot spot was generated. The SiG coil had superior thermal and electrical stabilities. However, a nonrecovering resistive zone could be generated because excessive Joule heat energy could be induced by radial current flow due to the existence of radial resistance that was mainly generated by silicon grease and nonsuperconducting materials including the substrate, stabilizer, and buffer layers within the high-temperature superconductor (HTS). Therefore, it is essential to consider critical Joule heat energy that is influenced by operating current and stored magnetic energy as well as the radial resistance to achieve self-protective 2G HTS coils. [ABSTRACT FROM PUBLISHER]

As a kind of future weapon, an electric launcher uses high current to drive projectiles reaching velocities on the order of several kilometers per second. As is known, high and rapidly changing currents through electric launcher can lead to strong radiation. A PSPICE model is used to analyze the frequency content of currents in the helical electromagnetic launcher (HEML) by nonuniform fast Fourier transform. The frequency spectrum is mainly determined by conducting duration and intensity of entering current. The main frequency of HEML is low, but high-frequency components can produce more radiation. The total radiation can be considerable. [ABSTRACT FROM PUBLISHER]

A model is developed to investigate the commutation process of a helical coil electromagnetic launcher (HCEML) structure. When the armature moves, the motion of the projectile coils’ magnetic energy would supply reactive power to move the leakage into and out of the coil windings of the launcher to accomplish the commutation. The energy conversion of the coil electromagnetic launcher can be considered as the process of energy transfer from the back commutation coils to the excited coils and then from the excited turns to the front commutation coils. In this paper, governing equations of the commutation were deduced theoretically, and finite-element model of HCEML was established in ANSOFT MAXWELL. Then a deeper circuit investigation into the overall performance of commutation was carried out by means of PSPICE software. The validity of the theoretical analysis and that of the circuit network model were finally verified by experiments. The results show that during the commutation process, the current of back commutation coils drops to zero with no energy remaining in the internal; the current of front commutation coils and drive–projectile coil system gradually changes to a stable value, which is related to the geometric parameters of the launcher; the drive–projectile coil system releases energy overall that is mainly used to increase the kinetic energy of the projectile; the power supply system has little effect on energy conversion and transformation at the commutating moment and just keeps the voltage and current from decaying due to the impedance and inductance of the launcher system. [ABSTRACT FROM PUBLISHER]

This paper presents a study on the effects of winding tension on the characteristic resistance of a no-insulation (NI) coil. Two ReBCO NI test pancake coils, having the same winding i.d. (60 mm), o.d. (67.6 mm), and number of turns (60), were sequentially prepared in a way that the first test coil was wound with a winding tension of 12-N, tested, and then rewound with a new winding tension of 20-N for the same tests. In each test, the test coil was energized at a target current, the power supply was “suddenly” disconnected, and then the temporal decay of the coil center field was measured, from which the time constant of the test coil and the consequent characteristic resistance were obtained. To check the reproducibility of experimental data, each test was repeated four times and each time the test coil was unwound and rewound with a given winding tension. The experimental results were analyzed with equivalent circuit analyses. Correlation between the winding tension and the characteristic resistance was discussed in detail. [ABSTRACT FROM PUBLISHER]