Relation between frictional loss and combination of thermal coefficient of bobbins and winding tension in AC superconducting coils

Mechanical loss in superconducting coils is one of the important parameters for the stability of high temperature superconducting coils (HTS coil). We prepared three kinds of impregnations (no impregnation, ionic liquid grease), measured the AC loss of the Bi-2223 tape under DC magnetic field in liquid nitrogen and quantitatively estimated the relation between the impregnation and losses. As a result, the loss can be reduced about 40% by using ionic liquid compared with no impregnation.We consider that the tape impregnated with ionic liquid is effective to reduce the AC loss. The results become fundamental data to reduce the AC loss of conduction-cooled HTS coils.

Section: Methodsmentioning

confidence: 99%

Influence of Mechanical Vibration and Losses Under AC Operating in Bi-2223 Tapes With Ionic Liquid Impregnation

Nakamura

Oka

Takagi

et al. 2012

“…An electric circuit for measuring AC loss measurement under the DC magnetic field is described in [10], and that under the AC magnetic field is shown in Fig. 3.…”

Section: Methodsmentioning

confidence: 99%

Mechanical Loss and Bobbin Materials in AC Superconducting Coil Under AC Magnetic Field

Takao

Masuda

Nishimura

et al. 2011

Self Cite

We made small superconducting coils and measured the total AC loss under the AC and DC external magnetic fields. The coil winding conditions are that 1, 5, and 10 N of the winding tensions and bobbin materials are glass fiber reinforced plastic (GFRP) and Dyneema fiber reinforced plastic (DFRP). The GFRP and the DFRP have thermal strain properties of contraction and expansion respectively with cooldown to cryogenic temperature. Mechanical losses were estimated from the measured data. According to the estimated mechanical losses, the loss of the coil whose bobbin material is the DFRP was small because the DFRP bobbin expanded and hence the winding was tightly fixed. Approximate 10 to 13% of the AC loss can be reduced by only changing the bobbin material from the GFRP to the DFRP.

“…To estimate the AC loss, a perpendicular component of the sample coil's voltage to the coil current was measured by the voltage between the coil's taps, and a slight phase error due to an inductive component of the signal was compensated by a cancel-coil signal in a lock-in amplifier. The method used is described in [5]. Fig.…”

Section: Electromagnetic Loss and Mechanical Lossmentioning

confidence: 99%

Effect of Thermal Cycles on Critical Current and AC Loss for Superconducting Coils Having Positive or Negative Thermal Expansion Bobbin

Takao

Yamamoto

Yamada

et al. 2008

Self Cite

We investigated the effect of thermal cycles between room and liquid-nitrogen temperatures on the critical current (Ic) and AC loss of two superconducting coils: one with a bobbin that expands during cooling from room temperature to cryogenic temperature and one with a bobbin that contracts during the cooling. After 100 cycles, neither bobbin suffered degradation. The Ic of the contraction-bobbin coil did not decrease, and that of the expansion-bobbin coil decreased due to the repeated thermal strain. The expansion coil's AC loss was significantly smaller than the contraction coil's loss at the first cycle; however, it increased with the thermal cycles and eventually surpassed the contraction coil's loss because the Ic of the expansion coil decreased due to the thermal fatigue. These results indicate that a moderate expansion in the size of the bobbin effectively decreases AC loss and that excessive expansion reduces the Ic and increases the AC loss.