Experimental study on the influence of fine particle mixing in gravel layers on the oil discharge efficiency of transformers

This study investigates water and transformer oil permeability in gravel layers with varied particle proportions. The specified experimental platform was established. 50-80 mm gravel samples and 1-10 mm particles were tested. The results indicate that for a 50-80 mm gravel layer, the permeability coefficient remains relatively unchanged when the mass fraction of fine particles does not exceed 12.7%. Once the mass fraction of fine particles exceeds 12.7%, the permeability coefficients for water and oil decrease according to a power function, with a more pronounced decrease in oil permeability. Combining ACE regression and experimental results, empirical formulas describing the permeability coefficients of water and oil in the gravel layer concerning the mass fractions of 5-15 mm and 1-5 mm particle sizes were derived as well. This research provides practical insights for optimizing gravel layer permeability in facility design and maintenance.