My theoretical mutterings:
In a normal transformer, the self inductance of the primary is high enough to limit current at the full primary voltage. This self inductance comes from the magnetic flux produced by the primary. Any secondary current acts to oppose the flux produced by the primary, forcing the primary to draw more current.
In a CT, the self inductance of the primary is very, very low. A CT can only work because we place a load in series with the primary circuit, and that load acts to limit current flow. In the ideal case, the actual voltage drop across the primary of the CT is a few mV.
The flux developed in the core of the CT is kept low because the current flowing on the secondary of the CT acts to oppose any flux developed by the primary.
The voltage developed in the secondary will always follow the standard transformer rule that the voltage developed in a wire by changing magnetic flux is equal to the rate change of the flux coupling that wire. Its just that in normal operation we arrange things so that the magnetic flux is quite low.
If you open circuit the secondary of the CT, then the core will almost certainly go into saturation, since you only have the primary current flow. If you know the core dimensions and the saturation flux density, then you will be able to estimate the total flux change per AC cycle, and from this you could estimate the 'average' voltage developed. Since the voltage developed is proportional to the rate of flux change, and we calculate the total flux change and the time period for that total flux change, we can calculate the average voltage.
However since the CT core is in saturation, we would expect that the flux will remain 'hard' at one polarity for most of the AC cycle, and then suddenly shift to the other polarity, with a very rapid transition. During this rapid transition, the rate change of flux is much higher than average, and the voltage developed in the secondary would be much higher than the average.
To answer the question, I guess what I would do is use the core characteristics to calculate the relationship between primary current and CT core flux (assuming an open secondary), use primary current to calculate core flux, and take the rate change of this calculated core flux to get secondary voltage.
-Jon