The insulating oil with low water content has high insulation level and is an important assurance of safe and stable operation of power grid. Thus

the water content of the insulating oil needs to be maintained in a low range and the problem about super hydrophobic filter membranes used for removing water from the insulating oil needs to be solved. In this paper

the super hydrophobic SiO

2

nanoparticles are uniformly bonded to the surface of the PP filter element

filter cloth

and filter paper by adopting the spraying method so to obtain the hydrophobic filter membrane. On this basis

the hydrophobic PP filter element is suitable for the large-flux primary filtration of insulating oil due to its low precision. The hydrophobic filter cloth combined

with tandem filter device is used for secondary stage filtration

which can withstand higher oil pressure while removing the water from the insulating oil further. The super-hydrophobic filter paper is suitable for the efficient tertiary filtration due to its outstanding ability of water removal. This multistage filtration can reduce the water content of the insulating oil below 10 mg·L

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. Multi-stage filtration not only has high water removal efficiency

but also meets the water removal requirements of different types of insulating oils.