Disturbance Analysis for Power Systems

Chapter 2

Phenomena Related to System Faults and the Process of Clearing Faults from a Power System

Power system disturbances are classified primarily as shunt faults. In this chapter we describe and analyze phase and ground shunt faults and their causes. Arc-over at the voltage peak represents a slow fault-creation mechanism when insulation fails, whereas lighting hits are random and may produce fault incident points at zero voltage. Faults occurring in power systems can therefore be either symmetrical or asymmetrical, depending on the fault incident angle. In addition, analysis of the nature of fault currents and their different modes of clearing from a power system is also covered and supported by DFR records and oscillograms. Fault modes of clearing, which can be either high speed, sequential, delayed local backup (breaker failure), or remote delayed backup, are also included. Power system phenomena related to the fault clearing process are described based on actual DFR records and oscillograms.

2.1 Shunt Fault Types Occurring in a Power System

As shown in Fig. 2.1, 10 different types of shunt faults can occur in a power system: three-phase faults, three phase-to-phase faults, three phase-to-ground faults, and three double-phase-to-ground faults. Protection against faults can be grouped as phase protection and ground protection. Traditionally, six electromechanical distance relays, three for phase connections and three for ground connections, are required to provide complete ...