Clever clogs (even though we could have an argument as to whether an increasing negative voltage constitutes 'rising' or 'falling')It's also rising for the 3rd quarter of the first cycle.{** I say quarter of a cycle, rather than the half-cycle you mention, since the voltage is only rising for the first half of the first half cycle}
However, what your failing to notice is that if the RCD really did operate during the first quarter cycle, there would be no current (rising or falling) during the third quarter!
Kind Regards, John.