Year-end Sale % OFF 
Abstract
The endurance of polymeric insulation foil is investigated under a mixed medium-voltage stress (DC + medium-frequency rectangular pulse) by means of accelerated lifetime testing. A dedicated setup is used that allows us to selectively eliminate the known risk factors for premature insulation failure under medium-frequency pulse voltage stress: partial discharges (PDs) during pulse transitions, excessive dielectric heating, and systemic overvoltages. The obtained results on polyethylenterephtalat (PET) insulation foil suggest that the adequate consideration of these factors is sufficient for eliminating the adverse effects of the pulse modulation under the investigated conditions. Indeed, if all mentioned risk factors are eliminated, the time to failure observed under a pure DC stress is shorter than with a superimposed pulse (keeping the same peak voltage). There is then no indication of an additional detrimental “per pulse” degradation process (i.e., the time to failure is not dependent on pulse frequency). In contrast, when repetitive PDs are present, the lifetime under combined DC + rectangular pulse stress strongly decreases with increasing pulse switching frequency. PD erosion of the foil is quantified by means of confocal microscopy, and the applicability of the streamer criterion for predicting PD inception is discussed.
Highlights
Medium voltage (MV, ≥ 1 kV) power electronic converters based on medium-frequency (MF, ≥ 1 kHz) energy conversion have stimulated numerous research efforts over the last years [1]
It is shown that above a threshold value of the pulse modulation amplitude, repetitive partial discharges (PDs) are present on the foil surface, leading to an insulation lifetime that decreases with increasing switching frequency
Repetitive PDs occur when the pulse amplitude exceeds a certain threshold value, and their presence results in a drastic decrease of insulation lifetime with increasing switching frequency. This reduction in lifetime can be explained by the erosive effect of the PDs: confocal microscopy of the foil surface shows that polymer material is removed below the dielectric barrier discharge plasma to a substantial fraction of the foil thickness
Summary
Medium voltage (MV, ≥ 1 kV) power electronic converters based on medium-frequency (MF, ≥ 1 kHz) energy conversion have stimulated numerous research efforts over the last years [1] These converters, sometimes called Electronic Transformers or Solid State Transformers, use semiconductor switches to interface a power grid with a load or generator via a MF MV transformer (and other passive components). By employing switching frequencies of several kilohertz and beyond, these converters achieve significantly higher power densities (at equal efficiency) than their low-frequency (50 Hz) counterparts because the magnetic components scale approximately with the inverse of their operating frequency [1] For these reasons, MV Electronic Transformers are expected to play a key role where actively controlled medium-voltage electrical energy conversion (AC-AC, AC-DC, DC-DC) is Energies 2020, 13, 13; doi:10.3390/en13010013 www.mdpi.com/journal/energies. Switching losses can be reduced significantly by the increased switching speeds (>10 kV/μs) [3], and a further increase in conversion power density is possible by increasing the switching frequency (up to and beyond 100 kHz)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
