Grounding a transformer is optional if the system has protective relays installed. He has also served as a private consultant since 1982. This guide contains. Abstract—Typically, high-voltage transmission systems are effectively grounded through the wye windings of transformers and autotransformers. Proper grounding ensures safety, minimizes electrical hazards, and enhances system stability, while protection mechanisms safeguard transformers against faults, overloads, and external. Abstract: Guidelines for protecting three-phase power transformers of more than 5 MVA rated capacity and operating at voltages exceeding 10 kV is provided to protection engineers and other readers in this guide.