Solid particles significantly affect the insulating performance of transformer oil

becoming one of the main causes of converter transformer outlet terminal faults. This study focuses on the migration and accumulation behavior of cellulose particles in a long oil gap under a DC electric field. A three-dimensional computational model is developed based on the discrete element method to investigate the motion characteristics of particles in oil and the formation process of particle chains

with comparative analysis against experimental results. The model first analyzes the forces acting on cellulose particles

where external field forces dominate particle motion

and inter-particle forces significantly influence particle accumulation. The effects of bipolar charging are also taken into account in the model. The discrete element model adopts a Lagrangian computational framework and uses a soft-sphere model to handle particle contact interactions. Computational results show that the development of particle chains involves dynamic processes of extension and breakage. With the reciprocating movement of particle chains between electrodes

the number of free particles in the oil gradually decreases

while cellulose particle chains increase

undergoing rapid extension followed by slower growth. Statistical results indicate that particle chains evolve from being dominated by short chains to longer chains

with shorter chains exhibiting relatively higher maximum velocities. Experimental results are consistent with the computation

demonstrating that the model effectively reflects the migration and accumulation characteristics of cellulose particles in a long oil gap.