Welcome Ben!.
I don't want to sound rude, but I would'nt like to give this sort of advice over the Internet without knowing what sort of protection on the system has operated and where that protection is in the system.
I would personally be checking any underground cabling first with the megger, before doing anything else. [Linked Image]
Obviously, if the system was working before the new Current and Potential Transformers were installed, logic would dictate that there is a fault in the installation of the CT's and PT's.
BTW, what brand/type of transformers are they? [Linked Image]

[This message has been edited by Trumpy (edited 01-08-2005).]