Distribution transformers are key components in power systems, functioning to change voltage levels for the distribution of electrical energy. The magnetic circuit's function is to provide a path for the magnetic flux produced by the electric current. The selection of core material for distribution transformers is standardized by PT PLN (Persero) through SPLN D3.002-1:2020, which permits the use of either CRGO steel or amorphous steel. No-load loss measurements were conducted using a no-load test. The results showed a loss of 41 Watts for the amorphous steel core distribution transformer and 89 Watts for the CRGO steel core distribution transformer. The reliability of amorphous steel core distribution transformers under high-load conditions was evaluated to determine the hotspot temperatures that arise during underloading, full-load, and overload operations. This was done to estimate the resulting loss of insulation life.Amorphous steel transformer 45,4℃ at 80% In, 54,6℃ at 100% In and 65,6℃ at 120% In while CRGO steel transformer was 55℃ at 80% In, 69℃ at 100% In and 82,6℃ at 120% In. The daily loss of insulation life was calculated for various loading conditions. For the amorphous steel core distribution transformer, the insulation life loss was 0.04227 hours at 80% loading, 0.11035 hours at 100% loading, and 0.38345 hours at 120% loading. The insulation life loss for the CRGO steel core distribution transformer was found to be consistently higher, with values of 0.1341 hours at 80% loading, 0.5673 hours at 100% loading, and 2.8326 hours at 120% loading. These results indicate that the CRGO steel core transformer experiences a significantly greater rate of insulation aging compared to the amorphous steel core transformer under all tested load variations.