Expert Tip #14: Rectifier Cabinets
What Type of Rectifier Cooling is best? Air or Oil?
Cathodic protection (CP) rectifiers generate heat due to the loss of energy as a result of converting AC power to DC. This is caused by the relative inefficiency of the internal components, such as the transformer and diodes. Therefore, this heat must be moved away from the rectifier components.
Air-Cooled Cabinets
Air-cooled cabinets use the movement of cooler air across the rectifier components to cool the components. Called convection, warm air rises and escapes through upper cabinet vents and then pulls cool air into the cabinet via the lower cabinet vents. This removes the heat from inside the rectifier cabinet to the outside environment. This is the most common type of cooling used for CP rectifiers. However, as convection draws in outside air, it also brings with it dust and possibly damp, corrosive air that can cause corrosion, thereby aging rectifier components.
Oil-Cooled Cabinets
Oil-cooled cabinets use the movement of transformer oil to cool rectifier components. Similar to air-cooled units, as the oil is heated, it rises and moves across the components. The heat in the oil is then dissipated through the cabinet walls and cooling fins into the atmosphere. The oil also protects the rectifier components from dust and corrosion, so oil-cooled cabinets may be more practical in dusty or humid environments. Oil-cooled rectifiers can be used in certain hazardous locations because any electrical arcing due to abnormal conditions in the rectifier is suppressed by the oil and is prevented from reaching the atmosphere.