Drainage device solid-state decoupler at insulated joint

In pipeline cathodic protection, as most pipelines are buried underground, the current pipeline anti-corrosion coating offers excellent insulation. However, coupled stray currents have increased. Once a pipeline passes through interference sources such as high-voltage lines, electrified railways, or power plants, it becomes susceptible to significant interference and high levels of stray currents. In some cases, high voltage and large currents can even damage the potentiostats used in cathodic protection. As a result, the entire cathodic protection system may fail to operate, leaving the pipeline unprotected and affecting its service life.

Solid-State Decouplers are AC interference protection products with the function of "blocking DC and passing AC." They offer high steady-state AC interference current tolerance, fault current tolerance, lightning surge discharge capability, and extremely low DC leakage levels. This product can be installed at locations where pipelines run parallel to or cross high-voltage transmission lines or electrified railways, as well as at centralized grounding points in stations and valve chambers. It provides protection against AC interference, fault currents, and lightning surges for metal pipelines while preventing the loss of cathodic protection current.

As a DC isolation and AC conduction device, it blocks the conduction of DC current within a certain voltage range, such as -2 to +2V or -3 to +1V, while providing a low-impedance path for AC current. When the voltage between the two terminals of the solid-state decoupler exceeds the DC conduction threshold, it enters a low-impedance DC conduction mode. When the voltage between the two terminals drops below the DC conduction threshold, it returns to a high-impedance state for DC current, cutting off the DC flow.
Solid-State Decouplers utilize the fast response characteristics of varistor-type surge protectors and the high current tolerance and low residual voltage characteristics of spark gap-type surge protectors to discharge and limit voltage from direct lightning strikes and induced lightning.

① Energy coordination between spark gaps and surge protectors. When a short-term high current occurs, the surge protector acts first, followed by the spark gap after 25ns. The conduction voltage is 45V, and the spark gap's rated discharge current is 50kA (10/350μs waveform for direct lightning strikes), effectively reducing the impact of strong current surges such as direct and induced lightning on the pipeline.

② When there is long-term DC or AC interference, diodes and capacitors activate, limiting the pipeline potential to between -1.4V and +0.7V, ensuring that the cathodic protection effect is not affected by discharge grounding.

③ By coordinating the energy handling of diodes, spark gaps, and surge protectors, the impact of DC and AC interference on the pipeline cathodic protection system can be eliminated.

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