KW Transformer Problem? Help!

[TJCOSS]

I have an old KW powering two mainlines that are interconnected via turnouts. Whenever I power up, the circuit breaker light comes on; I have no power, either track. I don't have to do anything to resolve the issue, other than to wait it out. Usually, after 20 minutes, a half hour, the circuit breaker resets and the trains will run normally for as long as I care to run them. This doesn't seem to me to be a normal short, as I don't need to do anything to resolve the issue. Additionally, the circuit breaker is open every time I first turn on the transformer. After it resets - no problems. ...until the next day, when the cycle repeats. Does this sound like a defective circuit breaker, or ....what? Thanks!