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We have studied ac losses of a conductive cooled high-temperature superconductor (HTS) coil. AC losses of a large stored energy HTS coil of 1.1 MJ were measured using the electrical method and the calorimetric method. The HTS coil is composed of 36 single-pancake coils using Ag-sheathed Bi2223 tapes and impregnated with epoxy resin. AC losses measured by the two methods were in good agreement. At low frequencies the experimental results were almost the same as the calculated hysteresis losses. With increasing the frequency, the measured values became larger than the calculated hysteresis losses. The extra losses were estimated to be eddy current losses generating at conduction plate made of pure aluminum and coupling losses generating between Ag sheathed tapes.