Types and circuits of DC decoupled devices

To prevent these high ohmic resistances, a breakdown fuse should be connected in parallel. Once the voltage drop on the resistor reaches the nominal value of the breakdown fuse, the fuse will blow immediately.

In the grid with resonant grounding, once a current fault occurs, the fault current or coil current or part of them will flow through the resistance for several hours. According to the scale of the power grid, the coil current can be as high as 400A. Connecting a π element consisting of a longitudinal choke and a transverse capacitor can avoid unnecessary loading when the fuse is broken through under transient overvoltage.

It's a very low resistance for cadmium, which is only 1 m Ω. The state of charge of the battery is secondary. The current and current stability of the nickel battery must be sufficient. They can be directly used as DC decoupling devices.

In normal operation, the fuse is not connected, because if you make it act, the battery will be short circuited and destroyed. When the cable is energized and the cathodic protection station is interrupted, the fuse is connected by closing the switch. The 1.2V NiCd battery can be isolated by removing the isolation cable. Finally, the grounding bus is closed to establish direct grounding. This battery is installed in the reverse order.

A polarized cell is an electrochemical module in which nickel or stainless steel electrodes are immersed in 50% KOH solution. Under the action of alternating current, because the electrolyte has good conductivity, and the passivation material with electronic conductivity has very low polarization impedance, the polarized battery has a resistance of several milliohm.

Since the grounding device of steel conduit is about negative 1V, it is necessary to implement cathodic protection for the steel conduit. If the diode is not connected to a high voltage threshold. When the cable structure is asymmetric or grid fault, the induced voltage in the steel conduit can exceed the threshold voltage due to the symmetrical load of the cable.

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