ABSTRACT
When cathodically protecting steel-reinforced concrete structures, the need for power is normally modest compared to that required for cathodically protecting steel structures in water or soil. For concrete, it is normal to use several small power supplies, each with an output of around 0.5-5 A and a maximum output voltage in the region of 8-10 V depending on the anode type. This can be compared to traditional cathodic protection (CP) systems
CONTENTS
10.1 Introduction ................................................................................. 161 10.2 Types of power supplies ................................................................ 162
10.2.1 Manual tap transformer + rectifier .................................... 163 10.2.2 Transformer + rectifier + smoothing circuit ...................... 164 10.2.3 Thyristor control ............................................................... 164 10.2.4 Linear ................................................................................ 165 10.2.5 Switch mode ...................................................................... 166
10.3 Features of power supplies ............................................................ 169 10.3.1 Protection against transients and lightning ........................ 169
10.3.1.1 Metal oxide varistor ............................................ 170 10.3.1.2 Transient protection diodes ................................. 171 10.3.1.3 Surge arrester ....................................................... 171 10.3.1.4 Weather station decoupler ................................... 171
10.3.2 Cabinet selection ................................................................ 172 10.3.3 Reading output currents, voltages and potentials .............. 175 10.3.4 Galvanic separation of power supplies ............................... 176 10.3.5 Power supply and reference electrode layout ...................... 177 10.3.6 Electromagnetic interference .............................................. 178 10.3.7 Efficiency ........................................................................... 179
10.4 Automatic systems ........................................................................ 179
where 200 A transformer rectifiers are common and single power supplies can have a capacity of 1000 A or more at up to 50 V. When protecting masonry structures, the difference is even greater as the current requirements are very low and the output is often in the region of 10-500 mA at around 4 V.
