Voltage-current characteristic of transformer oil under high electrical stress

M. Butcher, A. Neuber, H. Krompholz, J. Dickens, J. Qian, R. P. Joshi, K. H. Schoenbach

Research output: Contribution to journalConference articlepeer-review


The scattering cross-sections, transport coefficients, and details of the breakdown mechanism needed for describing current conduction in transformer oil at high applied voltages are virtually unknown. This makes it extremely difficult, if not impossible, to properly model electrical breakdown in oil. To address this issue, we have measured the V-I characteristic of transformer oil in the point-plane geometry for ∼3 mm gap widths. Three regimes can be distinguished. (1) For low voltages, V < 3 kV, the relationship between voltage and current is linear, exhibiting just resistive behavior within the measurement accuracy. (2) At intermediate voltages, the dependence is linear on a Fowler-Nordheim plot. (3) Between the breakdown voltage V B ∼ 30 kV and 10 kV, the current is proportional to V 2, indicating space charge limited current. Assuming a Schottky-type emission mechanism for electrons injected into the liquid, we derive an electron mobility of ∼6.0 × 10 -6 m 2/Vs, which is close to values reported in the literature before. Assuming Fowler-Nordheim emission leads to 3.8 × 10 -6 m 2/Vs. The ion mobility is believed to be more than one order of magnitude lower. At this point, it is difficult to gain any more detailed information on charge transport and possible multiplication based on simple analytical methods. Hence, we will apply our numerical modeling techniques already proven in analyzing high-field phenomena in polar liquids (e.g., water), to evaluate current conduction and the breakdown process in non-polar oil. By comparing our calculations with the experimental data, we hope to characterize important transport parameters, such as the electron ionization coefficient as a function of the electric field. We will also present our attempts to extract details of the field-dependent non-linear processes and electrode effects close to the breakdown regime.

Original languageEnglish
Article number4A9
Pages (from-to)258
Number of pages1
JournalIEEE International Conference on Plasma Science
StatePublished - 2004
EventIEEE Conference Record - Abstracts: The 31st IEEE International Conference on Plasma Science, ICOPS2004 - Baltimore, MD, United States
Duration: Jun 28 2004Jul 1 2004


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