The third cooling test of the 200 m superconducting DC power transmission system at Chubu University (CASER2) has been conducted from January to March 2011. During this term, the cooling of the system and the test of the liquid nitrogen circulation were performed. The temperature variation of the liquid nitrogen along the cryogenic pipe was measured and the heat leak from the surroundings at room temperature to the liquid nitrogen was estimated. The heat leak was about 275 W for 175 m of the

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... ogenic pipe, which was 55 % of the value obtained during the first cooling test. Further improvement will be continued to reduce the heat leak of CASER2.