Power transformers require a reliable isolation medium to maintain their performance and safety. One of these media is transformer oil which also functions as a coolant. The quality of the oil is greatly influenced by the level of moisture that enters through the transformer's breathing system. The silica gel in the breather is used to absorb the moisture, but its effectiveness decreases over time. This study aims to analyze the relationship between the condition of silica gel based on the length of use and the value of the breakdown voltage (BDV) of the transformer oil. The research method was carried out descriptively by taking data from BDV test results from two ONAN type transformer units at PT PLN Indonesia Power UBP Kamojang. The data obtained were analyzed to see the effect of silica gel conditions on changes in the transverse voltage of transformer oils. The results showed that transformers with silica gel that were replaced or properly maintained (Transformer 32) experienced an increase in BDV value from 63.2 kV to 73.5 kV. In contrast, transformers with unreplaced saturated gel silica (Transformer 8) experienced a drastic decrease in BDV value from 69.7 kV to 34.7 kV in a period of about eight months.