Partial discharge pulse sequence patterns and cavity development times in transformer oils under ac conditions

Pompili, M.; Mazzetti, C.; Bartnikas, R.

doi:10.1109/tdei.2005.1430407

Cited by 70 publications

(32 citation statements)

References 30 publications

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“…The PD can be considered as a point source and therefore the "pulse" has a spherical wave front which will be attenuated and reflected according to the acoustic impedances of the oil and steel through which it travels. It is also assumed that the pressure formula for the "explosion" of the PD moves with a spherical front is second order PDE equation (1).…”

Section: Problem Definition Simulation Results and Discussionmentioning

confidence: 99%

“…For insulation used in high temperature power equipment applications such as cables, transformers, and fault current limiters, PD is thought to be the primary degradation mechanism of the electrical insulation. One of the more common defects in a dielectric insulator is a void that forms as a bubble in the curing of an epoxy dielectric [1].…”

Section: Introductionmentioning

confidence: 99%

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Modelling of acoustic signals from Partial discharge activity

Ashraf¹,

Brian

Zhou

et al. 2006

2006 IEEE GCC Conference (GCC)

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Section: Problem Definition Simulation Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modelling of acoustic signals from Partial discharge activity

Ashraf¹,

Brian

Zhou

et al. 2006

2006 IEEE GCC Conference (GCC)

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“…The amplitude I 3 (t 3 ) of the third peak is about 50 % of that of the second peak I 2 (t 2 ). The peak times usually are 2-3 µs for t 1 , 6-8 µs for t 2 and about 15-18 µs for t 3 .…”

Section: Pulse Shape Analysismentioning

confidence: 99%

“…Due to the significantly lower electric strength of the gas in these voids, additional discharges may occur within a few µs after the initial one [3]. As each PD causes an individual impulse response of the band pass filter, a sequence of discharges as described above will lead to a superposition of the impulse responses of all PD that occur within the given time frame.…”

Section: Pd Measurements In Transformer Oilsmentioning

confidence: 99%

Pulse Shape Analysis of PD Signals – an efficient Tool to Monitor the Condition of Oils

Pätsch

Menzel²

2010

ijeei

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Partial discharges in oils are influenced by the actual dielectric properties of the liquid and especially degradation products may influence the phenomena. As a consequence of ageing processes in the liquid, oil molecules may be split into molecules of shorter lengths. The energy of a PD in the oil may heat the liquid locally and especially low molecular weight products in the oil will evaporate and form a gaseous phase within the liquid. This second phase can be generated in solids as well as in liquids. In solids the pressure in this gas phase will increase in accordance to the concentration of gas molecules. In liquids, an increase of the concentration of molecules will lead to an extension of the gas volume until the pressure within the void corresponds to the external gas pressure. Consequently, in accordance to Paschen's law gas discharges may occur in this gas phase immediately (i.e. within µs) after a PD that generated the gas filled void. The sequence will be so quick that commonly used equipment may not be able to monitor these discharges separately. Analyses of the pulse shape of the PD signals after the band pass filter showed differences in accordance to the degree of ageing of the oils examined. Possibilities to use characteristic parameters of the pulse shape for diagnostic purposes and especially their correlation to other dielectric properties will be discussed in detail. Experimental Procedure and Data AnalysisThe PD behaviour of oils from transformers used in different power grids was analyzed using a needle-plane arrangement with an electrode gap of 10 mm and a needle electrode with a curvature of about 5 µm. The voltage was increased linearly with about 2.5 kV rms /min up to approximately 15 kV rms and then kept constant for about 7 h or until 4000 PD pulses had occurred, whichever came first. With different oils different PD rates were found. In general, the oils had comparatively low PD rates, so in some of the measurements within 7 h only 500 PD occurred. Consecutive PD measured in oils are not correlated, they appear with a statistical distribution over time.The PD pulses are sampled after passing the 40 -400 kHz band pass filter of the PD detector. The shape of the oscillating signals after the band pass filter can be characterized by parameters such as the amplitudes I 1 , I 2 and I 3 of the first three peaks, their times of occurrence t 1 , t 2 and t 3 with respect to the trigger time, the zero crossings t 4 , t 5 and t 6 and the areas A 1 , A 2 and A 3 under the curve between the zero crossings, i.e. under the peaks. A special software extracts the analysis parameters, including those mentioned above, and creates a matrix for further processing. Figure 1 shows an impulse response of a calibration pulse (a damped oscillating signal) with these characteristic parameters.

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“…al. [7], assumed that negative PD inception voltage was lower than the positive one, and it was also valid for PD measurement under AC applied voltage. However, no experimental evidence was shown to support their assumption.…”

Section: Introductionmentioning

confidence: 99%