Cathodic protection requires DC isolation from ground for the structure being protected. Yet, at the same time, safety concerns exist regarding exposure to AC faults, AC induced voltage, lightning, or other electrical disturbances, which require solid grounding. Technology advances have led to the design of solid-state AC grounding/DC blocking devices, which can meet both requirements simultaneously. This technology has eliminated maintenance requirements, as compared to liquid-filled polarization cells. Common applications include over-voltage protection of insulated joints, mitigation of induced AC voltage, grounding AC power system faults, blocking stray DC current, and isolating electrical equipment on CP systems, such as motor-operated valves. The technology has been applied to pipelines, tanks, pipe-type transmission power cable casings, lead sheath cable casings, and other cathodically protected equipment. These applications are discussed in greater detail, with regard to safety requirements, codes, proper electrical ratings of devices, and resulting improvements in the cathodic protection system.
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