A comparison of physical properties of OF copper and ETP copper after holding at temperatures that simulate high voltage transformer use for up to one year

Three Oxygen Free copper alloys, C10100, C10500, and an experimental Cu-Ag alloy, and a C11000 Electrolytic Tough Pitch alloy were studied for physical property changes that would occur when wire samples of these alloys are subjected to the temperature encountered in a high voltage transformer during operation for up to one year. Hardness, Yield Strengths at 0.1% and 0.2% strain, Ultimate Tensile Strength and Elongation to failure were studied for times up to one year at 125°C. The benefits of using an OF C10100 alloy for transformers and other magnet wire products versus C11000 alloys are considered and highlighted. Metallographic comparisons are presented showing the changes in the alloys for the time studied. Recommendations are presented for transformer designers and consumers that incorporate the findings.