Effective methods of assessment of insulation system conditions in power transformers: a view based on practical experience

Соколов, В. В.; Berler, Z.; Rashkes, V.S.

doi:10.1109/eeic.1999.826289

Cited by 92 publications

(40 citation statements)

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“…However, tracking is now recognized as a significant feature at oil-cellulose interfaces and is considered a possible failure mode in large oil-filled transformers [5]. The term creeping discharge has been coined to describe the characteristic irreversible tree-like patterns occurring on the interface as a result of these surface discharges [6]. Surface tracking can deteriorate the surface resistance to such an extent that a sudden electrical discharge or breakdown can occur if the electrical stress is high enough.…”

Section: Introductionmentioning

confidence: 99%

Tracking and surface discharge at the oilߝpressboard interface

Mitchinson

Lewin

Strawbridge

et al. 2010

IEEE Electr. Insul. Mag.

103

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Section: Introductionmentioning

confidence: 99%

Tracking and surface discharge at the oilߝpressboard interface

Mitchinson

Lewin

Strawbridge

et al. 2010

IEEE Electr. Insul. Mag.

103

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“…As postulated, the field E(t) generates a total current density j(t), which can be written as follows (for E(t) = constant) (1) Under step d.c. "charging voltage" of magnitude , the polarization current i (pol) through the test object is as follows…”

Section: DC Conductivityand Permittivitymentioning

confidence: 99%

“…Dielectric properties including relative permittivity, dielectric dissipation factor andd.c.conductivity have been used as design and diagnosticparameters of insulation system conditions for power transformers [1].In order to design a power transformer, the interaction between oil and solid insulation material has to be considered and fully understood.It is known that when measuring dielectric properties of mineral oil and oil immersed pressboard(OIP), there are many factor that might influence the results i.e.live electrode curvature corner shape,contact between electrode and sample, temperature and electric field stress [2]. Further more, recently, researchers have been trying to measure dc resistivity of oil immersed pressboard (OIP) with higher voltage level as to simulate the real system, especially for HVDC [3].…”

Section: Introductionmentioning

confidence: 99%

Considerations for Dielectric Properties Measurements of Oil Immersed Pressboard

Pratomosiwi¹,

Pattanadech²,

Wieser³

et al. 2012

ijeei

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Dielectric properties including relative permittivity, dielectric dissipation factor (DDF) and dc resistivity has been used widely as a design parameter of insulation system. In measuring dielectric properties of oil immersed material (OIM), we have to make some adaptations from IEC 60093 and IEC 60250.This paper is focused on dielectric properties measurement of oil immersed pressboard (OIP) i.e. related to the effect of live electrode corner shape, the effect of electrode's weight, and the applied the electric field stress and temperature.In this experiment, the solid and liquid dielectric wereoil immersed transformer board type B 3.1A and operated under mineral oil bath, Nynas Nytro 4000x. We concluded that, round-cornered electrode yields steep electric field enhancement at the oil side. This phenomena makes it easier to generate oil discharge in the wedgewhen compared to sharp-cornered electrode. For measuring dielectric properties at high voltage level, this phenomenon should take into account. It was also found that electrode with pressure higher than 1.9 N/cm2 gives enough pressure to prevent a thin oil layer that present on surface.We also notice that for small g h ⁄ ratio (the gap of guard and guarded electrode is small compared to the sample) or thick sample, the fringing effect is high. Therefore calculation of effective area according to IEC 60093 is considerably applicable for thick sample. These results could be used as a consideration when measuring dielectric properties of oil immersed pressboardin compliment with IEC 60093 and IEC 60250.

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“…The accumulated charges can enhance the tangential electric field thereby initiating surface discharge activity. Sokolov et al have indicated that the creepage discharges in transformer insulation can cause carbonization of material [6]. In transformer insulation, one of the major cause for failure of solid insulating material is due to surface discharge activity causing carbonization of material.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Surface Discharge Activity with Thermally Aged Nanofluid Impregnated Paper Insulating Material

Swati

Sarathi

Sharma³

2017

ijeei

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SDIV of OIP material gets altered with thermal ageing temperature of OIP material, supply voltage frequency and the harmonic content in the supply voltage. The UHF signal radiated due to surface discharges formed under AC voltage, high frequency AC voltages and with harmonic voltages, have dominant frequency at about 0.9 GHz. Surface charge accumulation studies indicate that thermal ageing have high impact on amount of charge accumulation. Also number of layers of insulation have high charge trap density, which is ascertained through tdv/dt plot. The amount of charge accumulated is high with pressboard impregnated in titania nanoparticle dispersed transformer oil. The SD activity occurs at the rising portion of AC voltage and at high dv/dt's with harmonic AC voltages. More number of discharges occur with OIPs thermally aged at higher temperature. Physico-chemical changes clearly indicate not much of a change occurs with transformer insulation due to thermal ageing.

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Effective methods of assessment of insulation system conditions in power transformers: a view based on practical experience

Cited by 92 publications

References 0 publications

Tracking and surface discharge at the oilߝpressboard interface

Tracking and surface discharge at the oilߝpressboard interface

Considerations for Dielectric Properties Measurements of Oil Immersed Pressboard

Understanding the Surface Discharge Activity with Thermally Aged Nanofluid Impregnated Paper Insulating Material

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