I think you need to look at what's going on with your test. With the primary circuit equipment locked out and isolated and the secondary wiring disconnected, you inject voltage into the secondary and measure current in the secondary. As you step the voltage up, secondary current will increase in a basically linear fashion in relation to the injected voltage until you start saturating the core. As you near saturation, a small change in secondary voltage will make a larger change in secondary current.
You can plot this data and compare with published curves for your CT, or you can compare like items. As a rule of thumb, the saturation voltage will be a bit higher than the CT's accuracy class for C-class CT's.
Now, as to what happens when you fault? You can reconnect your secondary wiring and inject an amp at the CT terminals (or the closest terminal block to the CT for normal purposes)and again measure the voltage that your test set takes to push this amount of current. Here, the CT's winding is a high impedance path, so the vast majority of the current will flow through your protection scheme. With this voltage and current you can determine your current loop impedance and calculate your expected terminal voltage at the maximum calculated fault current. If you want to save yourself the calculation, take voltage it takes to push one amp and multiply that times 100. In either case, if the result is less than the saturation voltage you just determined, then your installation should not get into trouble with saturated CTs.
If you have too much circuit impedance, you can easily see what fault level will put the CT into saturation.
Now, since you're dealing with OCB's be sure that you check the saturation on all the CT's. they should be very close for equal ratings. I have seen cases where shifting hardware has shorted the primary path, causing those CTs to drastically drop in saturation due to the shorted primary path. In one case I investigated, this caused a misoperation of a protection scheme on and out-of-zone fault.
old field guy