Progress in Superconductivity and Cryogenics (한국초전도ㆍ저온공학회논문지)

The Korean Society of Superconductivity and Cryogenics (한국초전도저온학회)
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Measurement of outgassing rates of Kevlar and S-Glass materials used in torque tubes of High Tc Superconducting (HTS) Motors

  • Thadela, S. (Cryogenic Engineering Centre, Indian Institute of Technology) ;
  • Muralidhar, BVAS (Cryogenic Engineering Centre, Indian Institute of Technology) ;
  • Kalyani, B (Corporate R & D, Bharat Heavy Electricals Limited) ;
  • Choudhury, UK (Corporate R & D, Bharat Heavy Electricals Limited) ;
  • Yadav, SN (Central Institute of Plastics and Engineering Technology) ;
  • Rao, V.V. (Cryogenic Engineering Centre, Indian Institute of Technology)
  • Received : 2018.10.27
  • Accepted : 2018.12.27
  • Published : 2018.12.31
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Abstract

Torque tubes in High Temperature Superconducting (HTS) motor transfer torque from superconducting field winding rotor to the room temperature shaft. It should have minimum heat conduction property for minimizing the load on cryo-refrigerator. Generally, these torque tubes are made with stainless steel material because of high strength, very low outgassing and low thermal contraction properties at cryogenic temperatures and vacuum conditions. With recent developments in composite materials, these torque tubes could be made of composites such as Kevlar and S-Glass, which have the required properties like high strength and low thermal conductivity at cryogenic temperatures, but with a reduced weight. Development and testing of torque tubes made of these composites for HTS motor are taken up at Bharat Heavy Electricals Limited (BHEL), Hyderabad in collaboration with Central Institute of Plastics and Engineering Technology (CIPET), Chennai and Indian Institute of Technology (IIT), Kharagpur. As these materials are subjected to vacuum, it is important to measure their outgassing rates under vacuum conditions before manufacturing prototype torque tubes. The present study focusses on the outgassing characteristics of Kevlar and S-Glass, using an Outgassing Measurement System (OMS), developed at IIT Kharagpur. The OMS facility works under vacuum environment, in which the test samples are exposed to vacuum conditions over a sufficient period of time. The outgassing measurements for the composite samples were obtained using pressure-rise technique. These studies are useful to quantify the outgassing rate of composite materials under vacuum conditions and to suggest them for manufacturing composite torque tubes used in HTS motors.

Keywords

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Fig. 3. Schematic of the vacuum system used for outgassing measurement of torque tube materials.

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Fig. 4. Experimental setup for outgassing measurement of torque tube materials.

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Fig. 5. Pump-down characteristics without sample and with Kevlar/S-Glass samples in the test chamber as a function of time.

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Fig. 6. Pressure-rise in the test chamber as a function of time, after isolation from the vacuum pumps, without sample and for Kevlar/ S-Glass samples.

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Fig. 7. Outgassing rates for Kevlar and S-Glass samples.

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Fig. 8. RGA spectra of different gases for (a) chamber without test sample (b) chamber with Kevlar sample and (c) chamber with S-Glass sample.

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Fig. 1. (a) Schematic of HTS motor assembly, (b) 3D model of a composite torque tube.

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Fig. 2. (a) S-Glass sample placed inside test-chamber (b) Kevlar sample placed inside test-chamber.

TABLE I COMPOSITE SAMPLES USED FOR OUTGASSING MEASUREMENT.

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