The condensation and dehumidification theory of semiconductor which is Based on the principle of thermoelectric refrigerationis mainly the Seebeck effect and Perle effect. The Seebeck effect is the phenomenon that the N - type and P - type semiconductors convert thermal energy into electrical energy.howeverPerle effect is the opposite which converts electrical energy into thermal energy.thereforePerle effect plays a key role in the theory of thermoelectric condensation. Condensation and dehumidification is achieved through the direct current passing through one or more of the N - type and P - type semiconductors. In the refrigeration mode, direct current flows from N - type semiconductor to P - type semiconductor. In that casethe temperature of the cold end of the thermoelectric pair decreases meanwhilethe cold end of the thermoelectric pair absorbs heat from environment.The operational principle of dehumidifier for box-type transformer and control box is that hot and moisture air can condense when meeting the cold.Through electronic refrigeration methodCreating a regional temperature environment inside the product and using fan to make hot and humid air inside the box pass through that areain that casecondensation will continuously happenthen the condensed water is drained out of the electric box through special equipmentin this waythe moisture content inside the electric box will decrease the relative humidity will go downthe other area of electric box will not condense any more.