Microsecond and submicrosecond impulse breakdown of insulating liquids and liquid – polymer interfaces

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16459
Person Identifier (Local)
  • 201887148
Qualification Level
Qualification Name
Department, School or Faculty
  • From many years now industry has been searching for ways to reduce the environmental impact ofoperations. One area that has drawn attention within both the power and pulsed power industries is the use of mineral oils within large electrical machines and apparatus. Due to the advantageouscharacteristics ester-based dielectric fluids offer, such as high biodegradability, high flash and firepoints, low toxicity and high availability of raw material these fluids have been cited as a possiblereplacement for traditional mineral oil in high voltage (HV) power assets and pulsed power machines.Research has therefore focused on how these new fluids perform under the electrical stress typicallyexperienced during the operation of an AC power transformer. However, the standardised testingregimes used in such research are not completely representative of practical stress experienced bypulsed power apparatus. Pulsed power systems are commonly stressed with high impulsive voltages of non-standard wave-shape. This work addresses this gap in knowledge by providing a systematic study of the breakdown behaviour of ester fluids in an overstressed regime (i.e. breakdown ensured to occur on the rising edge of the impulse), while modelling a scenario more representative of bulk insulation within pulsed power machines; with liquid samples in varying levels of moisture saturation stressed with voltages of both standard and non-standard wave-shape to induce breakdown. To further reflect the practical scenario liquid samples were also tested when in direct contact with polymer dielectrics typically used in power and pulsed power machines. From the experimental work completed in this thesis it has been shown that both natural ester (Envirotemp FR3) and synthetic ester (MIDEL 7131) fluids offer comparable breakdown performance to mineral oil (Shell Diala S4) when used as a bulk insulating medium as well as when paired with practical polymer dielectrics as part of a liquid-polymer composite insulating system when stressed with both standard and non-standard voltage impulses. These findings will provide important data and information for researchers, operators and designers of high voltage power and pulsed power apparatus, facilitating better understand of the dielectric performance of environmentally friendly insulating liquids and leading to increased confidence in their implementation within large electrical machines.
Advisor / supervisor
  • MacGregor, Scott
  • Timoshkin, Igor
Resource Type