Listed below are references for your reading pleasure. Some of these might prove useful if you have limited experience in the actual design/maintenance of a utility electric grid:
Electrical References Transformers and Power Equipment - Anthony Pansini - Excellent, practical info on power equipment (transformers, breakers, fuses, meters, relays, etc.). As I'm looking I realize I'd forgotten how good this book is. Most of this stuff I know from having worked around it but if I'd remembered I would have taken this book in the test for moral support. Pansini has other good books too. His titles are worth Googling or Amazoning.
A Guide to Transformer Maintenance - J.J. Kelly, S.D. Myers, R. H Parrish - The bible of transformer maintenance. if you were marooned on a desert island, surrounded by the natives, their test equipment, and associated instruction manuals you would have no trouble in setting up their transformer maintenance program. I don't even know if they publish the book anymore but S.D Myers (the company) has a website devoted to transformer training.
Electric Power Engineering handbook/Leonard Grigsby and Electric Power Transformer Engineering/James Harlow - These are published by CRC Press. Their site is worth investigating for several other good titles also.
If I only bought one it would be the Pansini book. Supplement that with internet searches. In fact, if there are exam questions that stumped you I'd Google the heck out of them. The other books are good but, aside from building up your personal library, might be TMI. Your choice. To quote Edward R. Murrow, "Good night and good luck". (Google if you don't know who I'm talking about. His story is worth reading.)