Hi cheers
You should get some sample from current of your transformer , e.g with hall effect sensors and clamp method , thus with a simple comparator and current driver , you can give a command to your relays , to opening the circuits. remember , if your transformer is a power transformer , you can not open it under the load , simply . it will be dangerous and harmful .
and about smart relays , i think your mean is mini PLC ? if yes , you should amplify it's out put with powerful contactors.
Best Wishes
Goldsmith