Space charge inhibition effect of nano-Fe3O4 on improvement of impulse breakdown voltage of transformer oil based on improved Kerr optic measurements

Abstract

Transformer oil-based nanofluids (NFs) with 0.03 g/L Fe3O4 nanoparticle content exhibit 11.2% higher positive impulse breakdown voltage levels than pure transformer oils. To study the effects of the Fe3O4 nanoparticles on the space charge in transformer oil and to explain why the nano-modified transformer oil exhibits improved impulse breakdown voltage characteristics, the traditional Kerr electro-optic field mapping technique is improved by increasing the length of the parallel-plate electrodes and by using a photodetector array as a high light sensitivity device. The space charge distributions of pure transformer oil and of NFs containing Fe3O4 nanoparticles can be measured using the improved Kerr electro-optic field mapping technique. Test results indicate a significant reduction in space charge density in the transformer oil-based NFs with the Fe3O4 nanoparticles. The fast electrons are captured by the nanoparticles and are converted into slow-charged particles in the NFs, which then reduce the space charge density and result in a more uniform electric field distribution. Streamer propagation in the NFs is also obstructed, and the breakdown strengths of the NFs under impulse voltage conditions are also improved.

Effect of Fe3O4 nanoparticles on positive streamer propagation in transformer oil

“…Therefore, electrical field distortion in the oil can be alleviated by the increasing amount of negative charge carriers at the streamer tip and inside the streamer channels, which has been confirmed by Kerr electro-optic field mapping technique. 12 In addition, fast electrons lose more energy during these trapping and de-trapping process in shallow traps and ionization probability for oil molecules will be further decreased in nanofluid. In all, the presence of Fe 3 O 4 nanoparticles greatly increases the density of shallow traps and form more negative charges in the oil, which alleviates the electrical field distortion at the positive streamer tip and inhibits the propagation of streamer, improving its positive breakdown strength.…”

“…8,9,11 Some researchers think the potential well generated by induced or polarized charges on the surface of nanoparticles can capture the passing electrons and enhance the breakdown performance of transformer oil. 10,12 In comparison with the dielectric breakdown strength of nanofluid, its prebreakdown streamer propagation behavior is more important to understand the fundamental modification effect of nanoparticle, which can give valuable insight into the events leading to breakdown. Up to now, there is still dearth of knowledge about streamer propagation behavior in the transformer oil-based nanofluids and its relationship with nanoparticle modification.…”

Effect of the electrode material on the breakdown voltage and space charge distribution of propylene carbonate under impulse voltage

“…Furthermore, the is relatively significant for its high Kerr constant. In our previous works, [10][11][12][13][14] Kerr electro-optic measurement method is applied to investigate the space charge behaviors in liquid dielectrics such as propylene carbonate and transformer oil. Based on the space charge measurement results, the physical mechanism of space charge's effect on the breakdown process of liquid dielectrics is presented.…”

Magnetic liquids under high electric fields as broadband optical diodes

“…where K is the Kerr constant, which for ordinary liquids (transformer oils, for instance) is of the order of 10 −8 cm/(statVolt) 2 [35], and λ the wavelength of the propagating waves. One can show that it modifies Eq.…”