PULSED RECTIFIER LIMITATIONS FOR WELL CASING CATHODIC PROTECTION

Rectifier current pulses applied to deep well casings suffer considera ble waveform deterioration as well depth increases. Cathodic protectio n (CP) attributed to the use of a pulsed rectifier will not be effecti ve below a certain depth, which is a function of pulse characteristics and soil resistivity. A hypothetical 3,000-m length well casing is mo deled as a distributed lossy electrical transmission line. Below 300- to 500-m depths, the higher frequency of the pulse is severely attenua ted. Therefore, the CP process results at greater depths will not diff er significantly from those obtained with a nonpulsed DC rectifier.