How to choose the right clamp diodes for CT overvoltage protection
Just D1, or both D2 and D3 will prevent the voltage from straying too far from 2.5V. No point of having all of them. 320mV is so low I don't think you can find a TVS diode with a low enough reverse breakdown voltage. 

D2 and D3 clamp in forward bias. D1 clamps in reverse breakdown of one TVS and forward bias of the other (it is just two TVS diodes back-to-back). D2 clamps positive swing. D3 clamps negative swing.

Choosing the forward voltage drop of D2 and D3 to be different (or building your own bidirectional TVS by placing two  unidirectional TVS diodes with different reverse breakdown voltages back-to-back will result in assymetrical clamping above and below 2.5V.