Effects of air humidity and temperature to the activities of external partial discharges of stator windings

Binder, Erich; Draxler, A.; Muhr, M.; Pack, Stephan; Schwarz, Robert; Egger, H.; Hummer, Allan

doi:10.1049/cp:19990936

Cited by 7 publications

(1 citation statement)

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“…The influence of humidity on the PD behavior is not straightforward. On the one hand, an increasing relative humidity (RH) was found by several authors to decrease the PD activity [29][30][31] and to increase the insulation lifetime [32][33][34]. This was mainly attributed to a spreading of PDs over a larger area due to the increased surface conductivity, thus leading to less impact on concentrated locations [33].…”

Section: Introductionmentioning

confidence: 99%

Influence of mixed-frequency medium-voltage and environmental stress on the aging of epoxy

Küchler,

Färber,

Šefl

et al. 2023

J. Phys. D: Appl. Phys.

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Recent developments in power electronic technologies lead to new challenges for insulation systems. This contribution aims to clarify the influence of a broad range of mixed-frequency medium-voltage (MF-MV) and environmental stress parameters on the aging of epoxy insulation. For this purpose, test samples are stressed with an AC (50 Hz) or a DC voltage, superimposed with a pulse-width modulated (PWM) voltage (kHz range). An analysis of the samples’ health state is carried out after the aging by evaluation of potential aging markers (AC breakdown strength, dielectric permittivity, glass transition temperature, FTIR spectra). Although the main focus of this work is on aging below the inception of partial discharges (PDs), it was first confirmed that PD-related aging depends mainly on the peak voltage stress. In contrast, the results obtained by aging below PD inception suggests a dependence on the root-mean-square (RMS) of the applied voltage stress, and consequently on the energy dissipation. Aging in the PD-free regime was only observed at alternating electric field stress and high relative humidity (RH) or elevated temperatures. No influences of space charge and of the slew rate of the PWM voltage were observed. Remarkably, higher PWM frequencies lead to less insulation aging. This might be attributed to the increasing hindrance of polymer side chain movement at higher frequencies, as observed by dielectric spectroscopy. In addition, it is indicated that the aging mechanisms under mixed-frequency voltage stress result from superimposed single-frequency aging mechanisms and that aging is activated after a latency period. Of the investigated potential aging markers, only the residual breakdown strength revealed aging effects, which correlates with lifetime observations in the PD-free voltage stress regime. It is hypothesized that the aging mechanism is associated with arearrangement of the free volume in the polymer, followed by a localized breaking of van der Waals bonds.

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