Dielectric breakdown of epoxy and its use as insulation for a high-voltage anode cable connector

Author: Aaron Doherty

Doherty, Aaron, 2022 Dielectric breakdown of epoxy and its use as insulation for a high-voltage anode cable connector, Flinders University, College of Science and Engineering

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Epoxy is an organic polymer that can act as an insulator material for high-voltage applications. By adding non-conductive filler materials, the dielectric properties of the epoxy can be modified. However, published literature is indecisive as to the effect of adding aluminium oxide nano-scale fillers to epoxy will have on the resulting nanocomposite’s dielectric properties, especially under direct current (DC) conditions. Most implementations of epoxy as an insulator material are in power systems and involve alternating current (AC) conditions at commercial power frequencies, however medical X-rays are generated using high DC voltages. Thus, it is critical to understand the dielectric properties of epoxy under these conditions.

Samples of bisphenol-A based epoxy with low concentrations of aluminium oxide nanofillers were subjected to ramp voltages up to 120 kilovolts (kV), and the voltage required for the samples to fail recorded. Samples that survived this initial ramp voltage were then subjected to repeated step pulses at 120kV until failure. It was found that neat epoxy (no filler) had the greatest dielectric strength, with nanocomposites with 0.5% nanofiller performing the worst. Higher concentrations of nanofiller (1 and 2%) did not differ from the neat epoxy in a statistically significant way. Sample size was a limiting factor, with only four samples at each concentration produced.

Additionally, a high-voltage anode cable connector was designed and successfully potted using Micro-X’s potting techniques. The cable assembly was able to withstand voltages up to 132kV and pass the dielectric strength test as described in the IEC 60601 Medical Electrical Equipment standard and survive for over a year and a half of accelerated lifespan testing as of the time of writing. An X-ray image of a watch was produced using a Micro-X X-ray tube powered using this potted cable assembly.

Keywords: epoxy, dielectric breakdown, high voltage, X-ray, medical device

Subject: Engineering thesis

Thesis type: Masters
Completed: 2022
School: College of Science and Engineering
Supervisor: A/Prof Egon Perilli