Hi,
What the circuit does:
The first stage is a (poorly designed) amplifier and rectifier.
The second stage (also poorly designed) is a comparator.
But I don´t know how it is meant to work in combination with a current transformer.
Maybe the current transformer type and the current transformer wring could give more insight.
*****
I´ve done some "isolation fault detection" for an isolated high power application.
It basically introduces some very low frequency (far below mains frequency) signal into the isolated net (voltage limited, current limited) and checks whether there is current flow.
"Very low frequency" instead of DC is used to validate (correlation) the signal. So the output is more fail safe an thus more reliable.
Here the "very low frequency" may be generated by the PEN_ON signal.
But indeed it´s nothing more than guessing.
Klaus