Influence of AC and DC fields on streaming electrification of transformer oil

Electrostatic charging in transformer oils. Testing and assessment

“…Another liquid flow circuit for streaming electrification measurements, as shown in Figure 9, was used by Higaki and Miao [91] and the results were reported by Miao et al [92,93]. The authors used a n electrode system with two coaxial cylinders made of brass.…”

“…At a certain level of electric stress and a t certain temperatures partial discharges may occur. In practice, the highly charged oil flowing through transformer ducts reaches the top tank where the excessive charges may cause catastrophic failure [92]. Although low intensity discharges may not cause any increase in ECT, this may not be true in the case of intensive discharges [80].…”

“…due t o moisture content) further enhancement in streaming current is observed when energization is applied. The effect uf dc field is polarity dependent causing a change of the streaming current polarity which may vary with the dc field level [92]. At a certain level of electric stress and a t certain temperatures partial discharges may occur.…”

Flow electrification of transformer oil effects of mixed fields

“…Under steady state, the radial volume charge distribution in the oil side of the interface at any radius T is given by [8,11,15] where 6 is the Debye length, and p, ( z ) is the total charge contained in the oil per unit area of surface in which its buildup is determined by the balance of charge generation at the solid phase surface and the relaxation of charge to ground [15].…”

“…On the other hand, at very low frequencies near dc, the effect of that term becomes dominant. The effect of frequency of ac energization can be seen from Figure 3; where the radius T~ = 16.5 mm and the values of oil parameters are taken from [8] as …”