The current that flows through an element of a power system is a parameter that can be used to detect faults, given the large increase in current flow when a short-circuit occurs. For this reason, a review of the concepts and procedures for calculating fault currents will be made in this chapter, together with some calculations illustrating the methods used. Although the use of these short-circuit calculations in relation to protection settings will be considered in detail, it is important to bear in mind that these calculations are also required for other appli cations, for example, calculating the substation earthing grid, the selection of conductor sizes and for the specifications of equipment such as power circuit breakers.

Chapter Contents:

• 2.1 Modelling for short-circuit current calculations
• 2.1.1 Effect of the system impedance
• 2.1.2 Effect of rotating machinery
• 2.1.3 Types of fault duty
• 2.1.4 Calculation of fault duty values
• 2.2 Methods for calculating short-circuit currents
• 2.2.1 Importance and construction of sequence networks
• 2.2.2 Calculation of asymmetrical faults using symmetrical components
• 2.2.2.1 Line-to-earth fault
• 2.2.2.2 Line-to-line fault
• 2.2.2.3 Line-to-line-to-earthfault
• 2.2.3 Equivalent impedances for a power system
• 2.3 Supplying the current and voltage signals to protection systems
• 2.4 Calculation of faults by computer

Inspec keywords: fault diagnosis; power system faults; power system protection; calculation; short-circuit currents

Other keywords: current flow; power circuit breaker; substation earthing grid; fault detection; fault current calculation; short-circuit current calculation; conductor size; electricity distribution network protection; power system

Subjects: Power system protection