I am struggling to wrap my head around this. I understand that a transformer is not going to pass DC, and that every current transformer (CT) has some pass band. But what properties drive the high pass behavior, and how can I estimate what this corner frequency would be? I understand that it has something to do with the inductance of the primary, core material, etc. But if I know my turns ratio and core material is there some rule of thumb to estimate where the low frequency cutoff is? I read this article on CT design but I am still trying to grasp this. Perhaps if someone could draw an equivalent circuit for me showing whatever parasitic RLC components are in play.
You can arrive at an estimate by first calculating the inductance of the secondary. This may be on your data sheet, or it can be calculated from the number of turns, turn area, and core material. From there, the high pass response will depend on the input impedance to the amplifier you are using to buffer / amplify the sense signal off the secondary or the termination resistance (whichever is lower... probably the termination resistance). Specifically, it should be fl=Rterm/(2*pi*Lsecondary).