Grounding transformers are used with delta secondary transformers primarily to provide a neutral point for connecting single-phase ground loads and to enhance safety by ensuring proper grounding. Without a grounding transformer, connecting a phase to ground could lead to voltage surges and unsafe conditions, as the delta configuration does not allow for neutral current transfer. The grounding transformer helps minimize losses and maintains voltage stability by keeping potential differences within a known range. Additionally, it addresses phase shifts that may arise in doubly fed systems, ensuring compatibility with other sources. Overall, grounding transformers play a crucial role in industrial settings where large loads and safety requirements are present.