Effect of nanoparticle shapes on creeping flashover characteristics at the interface of nanofluid-impregnated pressboard

Recent studies have shown that the modifications to nanofluid-impregnated pressboards by different shapes of nanoparticles are different. To investigate the effect of nanoparticles shapes on creeping flashover characteristics at the interface of nanofluid-impregnated pressboard (NP), creeping flashover behavior of spherical nanoparticle fluid/pressboard (NSFP) and nanorod fluid /pressboard (NRFP) were compared to that of oil/pressboard (OP) which was used as a reference. Creeping flashover experiments under AC and positive and negative impulse voltages were carried out. Results show that the modifications by spherical and rod nanoparticles on creeping flashover strength are distinct and different: negative creeping flashover voltages of NSFP and NRFP are increased up to 32 and 15% respectively, and the positive ones are separately improved as high as 15% and 5%. Whereas, experiments under AC voltage reveal quite a different trend: creeping flashover voltage of NSFP and NRFP are almost increased to the same extent, nearly 18%, while partial discharge inception voltage improvement in the increment of the former is 5.6 times larger than that of the latter. Charge behaviors at oil/pressboard interfaces were displayed by thermally stimulated depolarization current method. Space charge accumulation at the surface of NSFP is much less than that of NRFP and the dissipation rate of the former is faster, due to a larger trap density and a lower trap energy level, which weakens electric field distortion and results in the improvement of creeping flashover strength. The underlying mechanism is that spherical nanoparticles have a specific surface area 1.3 times as large as that of nanorods at the same concentration, and it is a source of shallow traps.