This chapter defines the power system faults, the role of protective relaying, and the basic concepts of relaying. Power systems are built to allow continuous generation, transmission, and consumption of energy. Most of the power system operation is based on a three-phase system that operates in a balanced mode, often described with a set of symmetrical phasors of currents and voltages being equal in magnitude and having the phase shifts between phases equal to 120. The faults may be defined as events that have contributed to a violation of the design limits for the power system components regarding insulation, galvanic isolation, voltage and current level, power rating, and other such requirements. The faults occur randomly and are associated with any component of the power system. As a result, the power component experiences an exceptional stress, and unless disconnected or de-energized, the component is damaged beyond repair. In general, the longer the duration of a fault, the larger is the damage. This chapter further describes elements of a relaying system and defines the basic concept of a relaying scheme. In addition, the basic principles of protective relaying operation are discussed. More detailed discussions of each of the relaying solutions using the mentioned principles aimed at protecting different power system components are outlined. 2005 Copyright 2005 Elsevier Inc. All rights reserved.
