Effects of Frequency and Temperature on Partial Discharge Characterization of Stator Windings

Kantar, Emre; Eberg, Espen; Hvidsten, Sverre

doi:10.1109/ceidp49254.2020.9437438

Cited by 8 publications

(4 citation statements)

References 13 publications

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“…The overall effect of this is that during the application of VLF voltages, breakdown occurs at a higher voltage magnitude or after a long time of testing [18]. These observations are also in good agreement with the discussion in [19] that imply that the deposited surface charges have more time to decay further at VLF and thus, do not contribute to the local electric field at polarity reversal as opposed to at 50 Hz; thus increasing the interfacial PDIV and breakdown strength values.…”

Section: Discussionsupporting

confidence: 87%

Longitudinal Breakdown Strength of Wet-mate Solid-Solid Interfaces at VLF and 50 Hz AC voltages

Ildstad¹,

Dale²,

Kantar

2022

NORD-IS

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The 50 Hz AC breakdown strength of dry interfaces is known to strongly depend upon the mechanical properties, contact pressure, roughness of the surfaces, and the type of lubricant used at the interface. This paper aims to experimentally examine how these factors affect the longitudinal AC breakdown strength of interfaces assembled in water, so-called wet interfaces. The main aim is to obtain data relevant to the design of power equipment operating at very low frequency (VLF) or DC voltages.Experiments were conducted using identical specimens made from 4mm thick plaques of PMMA and plane sections cut from XLPE cable insulation. The findings were discussed with respect to expected dimensions of interface voids and contact regions, considering tribology-based contact theory, including the impact of surface roughness, modulus of elasticity, and applied mechanical interface pressure. The longitudinal 50 Hz AC breakdown strength values of wet samples were typically as low as 80 % of samples assembled in the air under dry conditions. In addition, the results verified previous findings that the AC breakdown strength strongly increases with reduced surface roughness, stiffness, and increased interface pressure. The breakdown values obtained during VLF breakdown testing were found to be 2 – 3 times higher than in the case of testing at 50 Hz AC voltages.

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Section: Discussionsupporting

confidence: 87%

Longitudinal Breakdown Strength of Wet-mate Solid-Solid Interfaces at VLF and 50 Hz AC voltages

Ildstad¹,

Dale²,

Kantar

2022

NORD-IS

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“…7) and total apparent charge per period-volume (Fig. 8) are inversely proportional to the PDIV, thus dependent on the void voltage and available electrical energy stored in the voids, as described in (7) and (8). The frequency-independent total apparent charge per period volume for the Group B bars indicates that voids must decrease in size, either physically or by means of short-circuiting, due to sufficiently higher surface conductivity at higher temperatures.…”

Section: B the Measured Apparent Charge Magnitudementioning

confidence: 91%

Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and AC Supply Frequency

Aakre

Kantar

Eberg

2023

IEEE Trans. Dielect. Electr. Insul.

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The main purpose of this study was to investigate if the application of very low frequencies for PD measurements in type II generator bar insulation is relevant when compared to applying power line frequency at different test temperatures. Laboratory experiments were performed on two stator bar types rated 6.4 kV and 7.4 kV, labeled as Group A and Group B. The stator bars were taken from service and spare part storage (pristine). The samples were preconditioned at the maximum test voltage of 1.5 U0 before sweeping the AC high voltage supply from 0.1 Hz and 50 Hz. The test temperature was varied between 20 °C and 155 °C. Investigation of cross sections of the generator bars was done to qualitatively describe the voids. The main results showed that the partial discharge inception voltage (PDIV) for Group A was temperature independent at 50 Hz and decreased by 40 % at 0.1 Hz with increased temperatures, whereas the PDIV for Group B was frequency independent and increased by 70 % with temperature. Similarly, the PD magnitude and total apparent charge decreased by 90 % for Group B with increased temperature, whereas it more than doubled for Group A with temperature. The tested bars from Group A showed significantly larger voids, located close to the copper conductors, compared to Group B, where voids were mainly located within the mainwall insulation. Results indicated that tests performed at 0.1 Hz cannot directly represent results obtained at 50 Hz. Using a wide range of frequencies and test temperatures broadens the understanding of the behavior of the voids inside the mainwall insulation.

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“…7) and total apparent charge per period-volume (Fig. 8) are inversely proportional to the PDIV, thus dependent on the void voltage and available electrical energy stored in the voids, as described in (7) and (8). The frequency-independent total apparent charge per period-volume for the VPI bars indicate that voids must decrease in size, either physically or by means of short-circuiting, due to sufficiently higher surface conductivity at higher temperatures.…”

Section: B the Measured Apparent Charge Magnitudementioning

confidence: 92%

Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and Frequency

Aakre¹,

Kantar²,

Eberg³

2023

Preprint

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Effects of Frequency and Temperature on Partial Discharge Characterization of Stator Windings

Cited by 8 publications

References 13 publications

Longitudinal Breakdown Strength of Wet-mate Solid-Solid Interfaces at VLF and 50 Hz AC voltages

Longitudinal Breakdown Strength of Wet-mate Solid-Solid Interfaces at VLF and 50 Hz AC voltages

Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and AC Supply Frequency

Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and Frequency

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