Power system fault calculations are invariably undertaken using the mathematical technique termed `symmetrical components' analysis (alternatively termed `phase-sequence components' analysis). A wealth of literature exists on this subject and therefore the purpose of this text is to provide an abbreviated, concise and relevant explanation focusing on fundamental concepts and practical requirements relevant to power network construction. There are numerous computer-based systems available for undertaking power system fault calculations, but instances arise in practice of where it is much quicker and convenient to undertake hand calculations (with the aid of a calculator), or even to carry out hand calculations as a rough check to provide assurance that a computer calculation is correct (since computer output depends on correct data input). Furthermore, the ability to undertake hand calculations most importantly requires a mastery of the principles and concepts involved. This in turn leads to an in-built understanding of comparative equipment impedances and the typical current flows that arise on the power system, i.e. an appreciation of numbers, scale and size. Suffice it to say that where an analysis of an extensive or complex part of the power system is concerned - then in those instances recourse to a computer-based solution is invariably essential.

Chapter Contents:

• 4.1 Power system fault analysis — requirements
• 4.2 Symmetrical components fundamentals
• 4.2.1 Symmetrical components — basic concepts
• 4.2.2 Practical determination of phase-sequence impedances
• 4.2.3 Phase-sequence impedances of an OHL (or HV cable)
• 4.2.4 Phase-sequence impedances of a star-delta transformer
• 4.2.5 Phase-sequence impedance of an auto-transformer
• 4.2.6 Phase-sequence impedances of an earthing transformer
• 4.2.7 OHL single and double circuit impedances
• 4.2.8 Impedances database
• 4.3 Generator short-circuit performance
• 4.3.1 Generator short-circuit considerations
• 4.3.2 Rotor and stator windings
• 4.3.3 Unloaded generator subject to three-phase short-circuit at generator terminals
• 4.3.4 Generator fault current — practical considerations
• 4.3.5 Loaded generator subject to a three-phase short-circuit at the generator terminals
• 4.3.6 Generator sequence impedances
• 4.3.7 Generator subject to an open-circuit
• 4.4 Sequence networks for common fault conditions
• 4.4.1 Sequence networks
• 4.4.2 Three-phase fault
• 4.4.3 Single-phase-to-earth fault
• 4.4.4 Phase-to-phase fault
• 4.4.5 Single-phase open-circuit
• 4.4.6 Phase-sequence current flow analysis
• 4.5 Maximum and minimum fault level studies
• 4.5.1 Maximum and minimum busbar fault levels
• 4.5.2 Maximum and minimum fault level studies — feeders
• 4.5.3 Use of maximum and minimum fault level studies
• 4.6 Fault currents — methods and techniques
• 4.6.1 Fault calculations — overview
• 4.6.2 Generator driving voltage
• 4.6.3 Methods and techniques
• 4.6.4 Use of circuit maximum and minimum fault levels
• 4.6.5 Fault current decrement and protection operation
• 4.6.6 Transformer tap changers
• 4.6.7 The infinite busbar
• 4.6.8 Comparative impedances

Inspec keywords: power system protection; fault currents; power system faults

Other keywords: power system fault calculations; computer calculation; power network construction; `symmetrical components' analysis; mathematical technique; power system fault analysis; computer-based systems; comparative equipment impedances; fault current

Subjects: Power system protection