Investigating why accelerated insulation degradation is increasingly the reason for power system failures
When a power system goes down, you might initially suspect a generator malfunction, bad weather, or even a cyberattack. However, Virginia Tech researcher Mona Ghassemi points out, the cause is often, and increasingly, an insulation failure.
Ghassemi, assistant professor of electrical and computer engineering, has received two of the most prestigious awards for young faculty, a $500,000 National Science Foundation (NSF) Faculty Early Career Development Program (CAREER) award and a $450,000 Air Force Office of Scientific Research (AFOSR) Young Investigator Program (YIP) Award. Both grants were awarded to investigate how insulators degrade when used with new technologies and under extreme conditions. This achievement is especially remarkable as they came in the same year. Only one other faculty member in ECE received both a NSF CAREER and a DoD YIP in the same year—Dan Stilwell in 2003.
Ghassemi’s CAREER award, titled “Accelerated Insulation Aging due to Fast, Repetitive Voltage Pulses from Wide Bandgap Power Electronics,” explores one of the issues that accelerates aging of insulation systems in electrical components as a consequence of exposure to high slew rates (ranging from tens to hundreds of kVμs) and repetitive voltages (frequencies ranging from hundreds of kHz to MHz) that originate from emerging Wide Bandgap (WBG)-based power electronics. This accelerated aging of insulation systems is expected to be the most significant barrier to the adoption of WBG-based systems.
“One of the merits of WBG devices is that their slew rates and switching frequencies are much higher than Si-based devices. However, from the insulation side, frequency and slew rate are two of the most critical factors of a voltage, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. The shorter the rise time, the shorter the lifetime. Also, lifetime decreases with increasing frequency,” explains Ghassemi. “Thus, although WBG devices can lead to high power density designs, their generated voltages pose a severe threat to insulation systems: the risk of component failure can occur within hours or even minutes.”
Component failure may lead to blackouts in power grids as well as failures in electric vehicles or aircraft that can impact the safety of the passengers. Although the degradation effects of using power electronics on insulation systems have been studied, they are limited to low slew rates and repetitions. There are no published experimental data for insulation degradation under voltages with high slew rates and repetitions, Ghassemi explains. “This research endeavor aims to characterize, model, through a theoretical-based Multiphysics approach, and mitigate the accelerated aging problem under WBG-based voltages.”
Insulators under harsh conditions
Most materials break down faster under harsh conditions, and the insulators Ghassemi studies are no exception—which is the focus of her YIP award, titled “Characterization, Multiphysics Modeling, and Mitigation of Insulation Material Degradation and Breakdown.”
Ghassemi’s objectives for this research include developing Multiphysics models to understand the mechanisms and phenomena behind breakdown in insulators under low pressure and in harsh environments, in this case with temperatures ranging anywhere from -60°C to 180°C, and humidity up to 100 percent.
Training the next generation of electrical insulation researchers
Throughout her research, Ghassemi will be training students at all levels, in the lab, in the field, and in the classroom. At the graduate level, she developed and is teaching a new course, Advanced High Voltage and Electrical Insulation Engineering (ECE 5984). She also has plans for K-12 outreach activities designed to attract women and minorities to electrical engineering.