Any test you do with the Transformer connected to the Feeders will come up with a near zero Resistance reading.
One other thing to consider is when the tester is disconnected from the Feeders, this will create an EMF equal to the Transformer's winding which will flow for a short amount of time. It will also burst a current on the Primary side of the Transformer.
Keep this in mind when working on Transformers.
The only thing to do for a proper test would be to open the Feeders at the Transformer while testing.
Scott S.E.T.
