Suggestion: References:
1. Mason C. R., "The Art and Science of Protective Relaying," John Wiley & Sons, New York, 1956, page 268 "Grounding Transformers"
Reference 1 includes the y-delta and zig-zag grounding (= earthing in some Countries or Territories) transformer explanations and applications. It features schemes without direct connections of grounding transformers to the feeder (or downstream power distribution network) having load being protected by the grounding transformer against ground faults.
2. Beeman D., "Industrial Power Systems Handbook," McGraw-Hill Book Company, Inc., New York, 1955, page 348 "Grounding Transformers"
The grounding transformers may be connected directly to the feeder (or downstream power distribution network), and then they are treated as normal transformers from the grounding protection schemes standpoint. Again y-delta and zig-zag transformers are treated. Zig-zag transformer is usually smaller since it does not have the secondary windings; however, it is rated for very short time of fault duration and then fault must be tripped. y-delta transformer is usually used for the longer fault duration to allow time for its clearance.