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Short Circuit Study

The importance of conducting thorough and detailed short-circuit studies and analyses of industrial and commercial power systems cannot be overstated. Electric power systems in industrial plants and commercial buildings are designed to serve loads in a safe and reliable manner. One of the major considerations in the design of a power system is adequate control of short-circuits or faults as they are commonly called. Uncontrolled short-circuits can cause service outage with accompanying production downtime, inconvenience, interruption of essential facilities or vital services, extensive equipment damage, personnel injury or fatality, and possible fire damage.

Objectives of Short Circuit study:

  • To verify that the protective device is closing and latching properly
  • Verify that the protective device is capable of interrupting the flow of power
  • Verify that the equipment can withstand large mechanical forces caused by the maximum short-circuit capacity
  • Verify the equipment’s ability to withstand thermal stress by checking its I2t value
  • Determine branch fault current under various conditions as required to determine protective relay settings and associated equipment ratings
  • As an input for the calculation of incident energy in Arc Flash Studies

Short Circuit study Execution:

  • Gathering of required inputs such as SLDs, component parameters, Grid X/R ratio, system fault level, generator impedance parameter and Power MVA rating
  • Modelling of the system using ETAP simulation software
  • Creation of various study cases and finalizing the worst case scenario
  • Finding the Maximum and Minimum short circuit current
  • Preparation of detailed report with recommendation if necessary

Uses of Short Circuit study Results:

  • To identify fault current at various buses and branches of the studied network
  • To find the symmetrical rms current, Peak current and short time withstand rating of equipment
  • The result of short circuit study is the input for Relay coordination and Arc flash studies

Reference Standards:

  • IEC 60909 Short circuit currents in three phase A.C systems
  • IEEE 3002.3 Recommended Practice for Conducting Short-Circuit Studies and Analysis of Industrial and Commercial Power Systems