Testing of low-voltage motor turn insulation intended for pulse-width modulated applications

Hudon, C.; Amyot, N.; Lebey, Thierry; Castelan, P.; Kandev, Nédeltcho

doi:10.1109/94.891989

Cited by 76 publications

(8 citation statements)

References 6 publications

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“…It has been shown [18] that (bulk) space charge evolves under inverter-type voltages that possess a DC offset (e.g., unipolar rectangular voltages). Thus, in addition to increased dielectric heating, several investigators also mention the possibility of space charge playing a role in premature failure, in particular, under DC-biased repetitive pulse voltages [19,20]. While it is well known that the distortion of the electrode field by space charges in the insulation bulk plays a key role under DC voltage stress [21], it remains unclear if the interaction of the highly dynamic electrode field with bulk space charge influences insulation aging, because the available studies do not allow to clearly separate the influence of dielectric losses from the potential influence of space charge.…”

Section: Introductionmentioning

confidence: 99%

Endurance of Polymeric Insulation Foil Exposed to DC-Biased Medium-Frequency Rectangular Pulse Voltage Stress

et al. 2019

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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.

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Section: Introductionmentioning

confidence: 99%

Endurance of Polymeric Insulation Foil Exposed to DC-Biased Medium-Frequency Rectangular Pulse Voltage Stress

et al. 2019

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“…Another example is the decrease in the PDIV at low pressures, which poses a problem in aircraft applications [27]. Moreover, the PDIV was found to be reduced for an increase in the ambient temperature [19,28], which correlates with reduced lifetime of polymeric materials subjected to PD activity at elevated temperatures [28].…”

Section: Introductionmentioning

confidence: 99%

“…If neither PD-related aging, nor dielectric heating were present in polymeric insulation, aging was observed empirically [28,[45][46][47], but the underlying mechanisms were not investigated in detail. In principle, aging in the absence of PDs and dielectric heating can also occur by electromechanical processes, for which different models were developed [48][49][50][51].…”

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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“…There is an associated risk of partial discharge for each voltage transition [12], and as such, switching at increased frequencies in the kilohertz range can also increase the corresponding damage rate. The partial discharge response of the turn-to-turn insulation system in a machine cannot easily be tested by conventional procedures [13] but is arguably more important than the phase-to-earth insulation system, given the ease by which extra insulation like slot liners can be added without a significant reduction in power density.…”

Section: Introductionmentioning

confidence: 99%

Experimental comparison of partial discharge between fast-switching pulse waves and square waves

Emersic

Cotton

2022

J. Phys. D: Appl. Phys.

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The behaviour of partial discharge has been examined for unipolar turn-to-turn–like waveforms with short 10 to 90% rise-times of approximately 25 ns. Such waveforms simulate what may be seen between turns on random-wound inverter-fed electrical machines driven by ultra-fast switching wide-bandgap power semiconductors. The influence of pressure, voltage polarity, and pulse duration was examined, with particular focus on environments relevant to aerospace. Pulse waves were observed to generate distinct partial discharge behaviour relative to square waves, with important implications for detection and lifetime assessment. Partial discharge likelihood for pulse waves at a given voltage was reduced, with comparable discharge activity requiring an additional several hundred volts at both ambient pressure and 116 hPa. Partial discharge events typically occur sooner after voltage rise for shorter duration pulses, whereas discharges occasionally occurred over 1 ms after voltage rise for longer-duration 10–100 Hz square waves at lower pressures, which may be outside the window of detection of some instrumentation. While observations and stochastic behaviour were interpreted within the context of space charge and the latest understanding of Volume-Time theory, some observations have not been able to be accounted for. These include observed stochastic trends between partial discharge delay time and unipolar pulse duration not correlating well, a reduced delay between voltage change and partial discharge activity during voltage fall relative to rise, and the lack of observed partial discharge activity after voltage fall for unipolar voltage pulse durations less than 50 µs.

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Testing of low-voltage motor turn insulation intended for pulse-width modulated applications

Cited by 76 publications

References 6 publications

Endurance of Polymeric Insulation Foil Exposed to DC-Biased Medium-Frequency Rectangular Pulse Voltage Stress

Endurance of Polymeric Insulation Foil Exposed to DC-Biased Medium-Frequency Rectangular Pulse Voltage Stress

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

Experimental comparison of partial discharge between fast-switching pulse waves and square waves

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