Hi,
Although I did a 2 Ch, 1600 smpls/s, 800 times/s true RMS calculations (V, I) plus P, Z, I_DC, V_DC, with 16 (15) bit output precision with an 8 bit AVR... I don't think that RCDs do it this way. I also did fast_ response RMS tools that are stable to 16 bits output RMS within 30ms
I think RCDs do it without semiconductors. But I'm not sure.
They don't need to care for waveform distortion, nor for high precision. It doesn't make much difference whether it is 29mA or 31mA (2mA/30mA means 6% or 4bit precision) ...
It just needs to be fast enough and reliable. I guess the tests are made with fairly pure sinewave.
Maybe 30ms magnetics reaction time and 10ms mechanical delay.
I guess there are informations in the internet how RCDs work.
I remember (thirty years ago) there was a (common mode) coil where all live wires and the neutral wires are wound around, plus an output winding that carries the difference current to make the switch to trip.
Klaus