Abstract: In a power plant, the overflow state existed in the expansion tank of the closed cooling water system for long time, and the makeup water percentage of the unit was higher. The method for finding the leakage point was expounded. The device existing leakage fault was replaced, and the makeup water percentage was decreased. The result in this paper provides reference for solving similar problems.

Key words: closed cooling water system, expansion tank, overflow, leakage point find, make-up water percentage