The corrosion caused by chemical reaction between metallic structures and surrounding mediums, such as soil or water .the (CP) cathodic protection system is used to protect metallic structure against corrosion. Cathodic protection (CP) used to minimize corrosion by utilizing an external source of electrical current which forces the entire structure to become a cathode. There are two Types of cathodic protection system (Galvanic current, Impressed current).the Galvanic current is called a sacrificial anode is connected to the protected structure (cathode) through a DC power supply. In Galvanic current system ,a current passes from the sacrificing anode to the protected structure .the sacrificial anode is corroded rather than causing the protected structure corrosion .protected structure requires a constant current to stop the corrosion which determined by area, structure metal and the surrounding medium. The rains, humidity are decrease soil resistivity and increase the DC current .The corrosion and over protection resulting from increase in the DC current is harmful for the metallic structure. This problem can be solved by conventional cathodic protection system by manual adjustment of DC voltage periodically to obtain a constant current .the manual adjustment of DC voltage depends on experience of the technician and using the accuracy of the measuring equipment. The errors of measuring current depend on error from the technician or error from the measuring equipment. the corrosion of structure may occur when the interval between two successive adjustment is long .An automatically regulated cathodic protection system is used to overcome problems from conventional cathodic protection system .the regulated cathodic protection system adjust the DC voltage of the system automatically when it senses the variations of surrounding medium resistivity so the DC current is constant at the required level.
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