The effect of oxidative and paper degradation impurities on partial discharge characteristics of hexadecane

Abstract

Partial discharge (PD) characteristics of hexadecane were studied in a needle-plane electrode geometry under AC field with a tungsten needle of 20 m tip radius. PD experiments were conducted on samples containing known concentrations of oil/paper degradation compounds. Partial discharge inception voltage (PDIV), streamer repetition rates, and phase resolved PD (PRPD) patterns were acquired. Ionization potentials (IP) and electron affinities (EA) of hexadecane and a selection of additives were calculated with density functional theory (DFT) and correlated to PD characteristics. IP did not have a significant effect on the number of streamers initiated as most additives had higher IP relative to hexadecane. The presence of electronegative oxygen changes substantially the PD characteristics and, for most additives, increases the number of positive and negative streamers initiated. The greatest changes in PD characteristics, a reduced number of negative streamers, was observed for compounds with large electron capture cross section, even those with negative EA.

Partial discharge based diagnostics for impurities in insulating fluid

“…All measurements in [6][7][8] and in this paper were conducted with a needle-plane electrode geometry installed in a 400 ml test cell. A tungsten needle of 3 cm length, 1 mm diameter, and 20 m tip radius and a 5 cm diameter aluminum plane electrode was employed with a fluid-filled gap separation of 1 cm from the needle tip to the barrier of the plane electrode.…”

“…A tungsten needle of 3 cm length, 1 mm diameter, and 20 m tip radius and a 5 cm diameter aluminum plane electrode was employed with a fluid-filled gap separation of 1 cm from the needle tip to the barrier of the plane electrode. A detailed schematic of the test cell is given in [7]. The PD characteristics were measured using a BAUR DTA 100C Breakdown Tester modified to incorporate a conventional PD coupling circuit in accordance to IEC 60270 [9].…”

“…Previous research developed an experimental approach to analyzing the effect of chemical impurities on PD characteristics as a basis for condition assessment of dielectric fluids [6][7][8]. The technique is based on a needle-plane electrode geometry with a barrier insulation at the low-field plane electrode to preclude needle damaging breakdowns and facilitates acquisition of PDIV, discharge rate, and phase resolved PD (PRPD) patterns under well-defined conditions.…”

“…Initially, the objective of the work was to correlate changes in PD characteristics with the concentration and electrochemical properties of a low ionization potential (IP) compound, N,Ndimethlyaniline (DMA), and a high IP compound with a large electron capture cross section, 1,1,1-trichloroethane (TCE) [6]. Further studies were conducted on naturally occurring degradation products associated with oxidation of the dielectric fluid, overheated cellulose [7], aromatic compounds, and corrosive sulfur compounds commonly found in mineral oil used for electrical insulating applications [8]. Density functional theory (DFT) calculations on IP and electron affinity (EA) of various additives were conducted and correlated to their PD characteristics.…”

“…All studies were conducted with the paraffinic hydrocarbon, hexadecane, purchased from Chevron Phillips. Hexadecane provides a relatively pure base fluid with a molecular weight distribution very similar to that of common dielectric fluids used in transformers [7].…”