Oil-paper insulation is the most commonly used main insulation material for large converter transformers

which is composed of solid and liquid phases

and the electric double layer (EDL) exists at the solid-liquid interface. The measures such as regulating the characteristics of EDL at the oil-paper interface

decreasing the charge concentration in the EDL region of the interface

and lowering the interface barrier

are conducive to reducing charge accumulation at oil-paper interface under the applied voltage in oil-paper composite structure

accelerating charge dissipation at oil-paper interface after removing the applied voltage

and reducing the local electric field distortion under special operating conditions such as polarity reversal. Aimed at the composite insulation material composed of mineral insulating oil and cellulose insulation paper

combined with traditional macroscopic measurement methods and new microscopic analysis methods

the charge distribution characteristics and regulation methods of EDL were explored. Based on density functional theory

the oil-paper interface model is established

and the electron affinity of its constituent molecules and the differential charge at the oil-paper interface are calculated. The results show that the electron affinity of the main component molecules of mineral insulating oil is positive

while cellulose molecular has a negative electron affinity

which leads to the spontaneous affinity to the negative charge. Therefore

the surface of the insulating paper is negatively charged

and the insulating oil is positively charged. In order to weaken the interface barrier effect caused by EDL

additional hole traps should be introduced to the surface of the insulating paper with additives. According to the partial density of states of the oil-paper interface

3-amino-1

2

4-triazole

N

N'-di-tert-butyl-ethylenediamine and phenyl-alpha-naphthylamin molecules can act as hole acceptors

tend to adsorb positive charges

and can form hydrogen bonds with cellulose molecules to easily attach to the insulating paper surface

thereby reducing the negative charge adsorbed on the insulating surface. According to the zeta potential of EDL at the oil-paper interface obtained by microelectrophoresis

the Zeta potential of the electric double layer at the oil-paper interface was reduced by 9.8~16.1 mV with 3-amino-1

2

4-triazole

N

N'-di- tert-butyl-ethylene- diamine and phenyl-alpha-naphthylamin additives

which proves the effectiveness of the electric double-layer regulation at the oil-paper interface

and also provides a reference for the selection of insulating oil additives.