The advise sounds OK, if you have the surges on the primary side of the transformer, except I would also suggest an MOV on the primary side of the transformer. The MOVs need rating at the line voltage plus 10% to allow for variations in the supply voltage, plus another 10% to allow for the tolerance on the MOV itself, otherwise you could end up very short MOV life. As I have read your posting you have a primary voltage of 120VAC, therefore plus 10% = 132, plus another 10% = 145VAC. The nearest standard MOV rating is 150VAC. On the secondary side the voltage is 220V, therefore plus 10% =
242, plus 10% =262V rms. The nearest standard MOV voltage easily available is 275V rms. To protect the MOVs form going off with a bang when it fails you should fit a fuse in series rated at the full load current of the fan(s). To size the MOV is no easy, but if you can post the fan's full load current(s) I will try and advise you.
If the surges are actually been generated by the fan, this will need a better suppression circuit on the secondary side of the transformer. Do you have a on/off contactor or relay in the circuit where you switch the fans on and off? If the surges are due to the fans I would suggest MOVs line to line and line to ground, (three MOVs). This offers the best protection. again the sizing of the MOVs depend on the full load current.
On similar systems I have measured surge voltages of 5000 volts, but with a supply of 480V, these were reduced to less than 700 volts peak once the MOVs were installed. you can also add a simple RC network to help reduce the peak value.
MOV can be dangerous so please read the Littlefuse publications regarding there installation for more detailed information,
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Do not try installing MOVs in parallel as it does not increase the ratings due to the tolerances on the MOV's voltage, fit a larger MOV.
Hope this helps