This guide provides a comprehensive overview of various transformer protection schemes and offers recommendations for relay selection, coordination, and settings. Another important standard is the IEC 61850, which focuses on communication protocols for substation automation systems. George Rockefeller is President of Rockefeller Associates, Inc. He has a BS in EE from Lehigh University, a MS from New Jersey Institute of Technology, and a MBA from Fairleigh Dickinson University. Some of applications are small and large transformer infeed, dual infeed with single transformer, parallel incoming transformer feeders, and others like parallel incoming. 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. In some cases, a user may apply the techniques described in this guide for protecting. This document supplements PJM Manual 07 which contains the minimum design standards and requirements for the protection systems associated with the bulk power facilities within PJM. Overcurrent Protection Protects against overloads and external short circuit faults: 2.