If the smoke got out of it it's bad. ;-)
Most transformers are 110v and 220v be sure how you are wiring
it. I this is a Hayward heater you can find a book for it at
Their are a couple of different heaters but they should all take the same transformer. I would go ahead and find the correct heater and print the book so you have it.
Once your sure of the wiring
make sure you have the proper power going to the unit. To say if it is kicking the breaker you may just be getting half the power to come back on. Then unhook the transformer from the heater and see how much power you have. If your not getting a full 24v you may have burnt half the transformer. This means a new transformer. If it is still kicking the fuse you need to check all the wiring
to the box and make sure that your problem is not there. If it's not kicking the fuse and you have good power, It will be in your heater and you will have to go through that to check for shorts. Your book will have a trouble shooting flow chart to help with this. Good luck.