Date Approved

6-23-2020

Embargo Period

6-24-2020

Document Type

Thesis

Degree Name

M.S. Mechanical Engineering

Department

Mechanical Engineering

College

Henry M. Rowan College of Engineering

First Advisor

Xue, Wei

Second Advisor

Krchnavek, Robert

Third Advisor

Bakrania, Smitesh

Keywords

Cryogenic temperature, Dielectric breakdown, Electrical treeing, Nanocomposites

Subject(s)

Low temperature engineering; Superconductors; Electric cables

Disciplines

Electro-Mechanical Systems | Mechanical Engineering

Abstract

In this thesis, polyimide (PI) and silicon dioxide (SiO2) were combined in the form of a nanocomposite for use as a dielectric on helium-cooled high-temperature superconducting (HTS) cables. Further, a cryogenic chamber was designed with the intent of cooling samples to 40 K for dielectric and thermal contraction testing. Composites were created through an in situ process which resulted in nanoparticle formation within the host matrix. Samples were tested for dielectric strength at room temperature (300 K) as well as cryogenic temperature (92 K) using liquid nitrogen as the coolant. Composite samples tested at 300 K averaged a dielectric strength of about 175 kV/mm, while those tested cryogenically exhibited an average strength of around 275 kV/mm. Samples were imaged via scanning electron microscopy (SEM) both before and after dielectric testing. Imaging samples broken down at 92 K revealed evidence of electrical treeing, a breakdown mechanism discussed in this thesis. Finally, the helium chamber has been designed to accommodate multiple testing systems at cryogenic temperatures. Although this research is ongoing, the PI/SiO2 composite is already a promising candidate as a cryogenic HTS cable dielectric.

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