How can I find the loocation of a break in a 240V underground circuit to an outside storage building
You need a cable locator this is very much like a wire tracer but it uses the ground as part of the circuit. You transmit a signal over the cable and the signal returns through the ground to your receiver. 

You normally use it to trace where a cable is located but you can use it to find a break in the cable as the sound will drop out suddenly where their is a break in the cable. 

https://www.youtube.com/watch?v=PP_-TEKMNXc