Comments on There are RCD units for DC exist. How do they sense the small DC current difference?
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There are RCD units for DC exist. How do they sense the small DC current difference?
There are GFCI (RCD) units for DC. How do they sense the small DC current difference?
I understand how GFCI for AC works. It uses a differential current sensing transformer with two opposing primary windings and a sense winding. The turns ratio would be on the order of 1:1:1000. But a transformer is an AC thing. What’s done for DC?
There’s this board-level module which can detect 6 mA DC currents.
Then this high level white paper mentions GFCI for DC on p.5 . But it sounds more like a neutral-ground fault detection. In addition, the secondary winding on the left of the diagram has a third terminal for earth ground, which confuses me.
It may seem strange to use a current transformer to detect a DC ground fault current. However this is achieved by driving the CT [current transformer] core into and out of saturation at a certain frequency, and using the DC fault current to generate a detectable change in the saturation characteristics. [page 5]
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