Implications of Nonlinear Material Parameters on the Dielectric Loss under Harmonic Distorted Voltages

Thomas Linde,Stefan Kornhuber,Jun Ting Loh,Stephan Schlegel,Steffen Großmann,Karsten Backhaus

doi:10.3390/en14030663

Thomas Linde, Stefan Kornhuber + Show 4 more

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https://doi.org/10.3390/en14030663

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Abstract

The increasing number of power electronic devices in electrical grids may lead to harmonic distorted voltages, which are considered to be possible causes of component failures. In this study, the dielectric losses of epoxy polymer and functionally filled silicone rubber (f-SiR) samples are investigated under harmonic distorted voltages in terms of their dielectric losses and the consequent heat source density within the material. The results suggest that the epoxy polymer samples behave linearly to the electric field strength and therefore allow good predictability of the dielectric losses. The investigated f-SiR samples exhibit a nonlinear behaviour when an electric field threshold is exceeded. The subsequent direct loss measurements under harmonic distorted voltage reveal a sharp rise of the dielectric loss with increasing electrical field strength. This leads to a higher risk of excessive heat in the material when harmonics are present. In conclusion, the investigation highlights the difficulties of estimating dielectric losses in nonlinear dielectric materials when distorted voltages are present.

Highlights

Accepted: 23 January 2021The increasing number of inverters and power electronic converters in mediumvoltage (MV) grids can lead to the distortion of voltage waveforms [1,2,3]
The measurements of the DC conductivity, AC dielectric properties and the heat source density under harmonic distorted voltages conducted on both epoxy polymer and filled silicone rubber (f-silicone rubber (SiR)) samples are presented
The calculated conductivity of three epoxy polymer samples was reproducibly below κ = 5 · 10−16 S m−1 at 23 °C when stressed with the highest utilisable electric field strength of 1 kV mm−1

Summary

Introduction

Accepted: 23 January 2021The increasing number of inverters and power electronic converters in mediumvoltage (MV) grids can lead to the distortion of voltage waveforms [1,2,3]. A well-investigated and frequently-cited example is the Eagle Pass back-to-back tie, where cable terminations with stress grading failed because the stressing voltage contained high frequency components [10]. 12.4 kHz (207th harmonic) were present and caused significant additional dielectric losses in the stress grading layer, which led to the failure [10]. The Eagle Pass example, already several years in the past, demonstrates that power electronic devices introduce new challenges to the design of insulation and the requirements of insulation materials. It is not an isolated case as a recent review of MV cable termination failures showed [1]

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