short circuit studies

SHORT CIRCUIT STUDY – EXECUTIVE SUMMARY
Short Circuit in a system is caused accidentally either due to insulation failure or flashover over lines initiated by lightning or accidental faulty operation. The above phenomenon results in the flow of heavy short circuit currents through the equipment which may result in permanent damage to power system elements. Hence, it is important to ensure that the short circuit ratings of power system elements are adequate. In addition, the faulty parts need to be disconnected from the healthy power system network using circuit breakers, fuses, and other protection devices to protect the power system from further damage. The software used for short circuit studies is ETAP, DigSilent Powerfactory, PSS/E, and so on.
WHY SHORT CIRCUIT STUDY?
• To determine the magnitude of current that flows through the system during fault conditions
• To determine short circuit ratings (breaking current – AC and DC components, peak making current and short time withstand ratings) of switchgear, circuit breakers, and other power system elements.
• To determine the permissible operating configurations that ensure the short circuit ratings are within the capability.
• As an input for the design of the protection system (breaker/relay/release/CT/secondary circuits) and to calculate optimum protection settings.
• As an input for the calculation of incident energy in Arc Flash Studies.
HOW DO SHORT CIRCUITS STUDY? (METHODOLOGY)
• Collection of inputs (SLD, equipment parameters – Voltage kV rating, Power MVA rating, Impedance, System fault level, X/R ratio, etc.)
• Modelling in study software.
• Finalizing the study case scenarios
• Carrying out simulation
• Review of results and recommendations, wherever necessary
• Submission of detailed report
• Presentation of study findings
OUTCOMES OF SHORT CIRCUIT STUDY
• Detailed report explaining the input data, study cases, observations, and recommendations
• Fault currents at various buses and branches in the system
• Breaking current – AC and DC components, peak making current and short time withstand ratings of equipment
• Input to relay coordination study
• Input to Arc Flash Study
REFERENCE STANDARDS
ANSI/IEEE C37
IEC 60909
IEEE 3002

 
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