This chapter considers the combination of relays required to protect various items of power system equipment, plus a brief reference to the diagrams that are part of substation design work. A general knowledge of these diagrams is important in understanding the background to. The Control and Protection System technology in a substation is very important because it watches over, protects, and manages the flow of electricity. Because substations are getting more complicated, more power is being sent, and fault currents are getting higher, which means that control and. Previous chapters have detailed the make up and operating characteristics of various types of protection relays. We hope you will find it useful in your work. In HV (High Voltage) and MV (Medium Voltage) substations, relay protection safeguards critical assets such as transformers, circuit breakers, and lines. Effective relay protection depends on. Generator protection covers: phase-to-phase short circuits in stator windings, stator ground faults, inter-turn short circuits in stator windings, external short circuits, symmetrical overload, stator overvoltage, single- and double-point grounding in the excitation circuit, and loss of excitation. This series of courses are based on the “Design Guide for Rural Substations”, published by the Rural Utilities Service of the United States Department of Agriculture, RUS Bulletin 1724E-300, June 2001.