Short Circuit Studies, Fault Calculations
Short circuit calculations provide currents and voltages on a power system during
fault conditions. This information is required to design an adequate protective
relaying system and to determine interrupting requirements for circuit breakers
at each switching location. Fault conditions can be balanced or un-balanced shunt
faults or series (open conductor) faults. Often information about contributions
to a fault from rotating machines such synchronous machines, large motors would
be required as a function of time to determine making and breaking requirements.
Fault calculations may consider or ignore pre-fault power flow conditions. Short
Circuit is the PowerApps analysis module dedicated to simulating fault conditions
in three-phase electric power systems. User friendly data entry, a multitude of
reports and flexibility in applying all industry-accepted standards are features
that make it an Indispensable tool for these very common and important system studies.
PowerApps Short Circuit Module adheres to North American ANSI C37.5, ANSI C37.010,
ANSI C37.13 and International IEC-60909 guidelines. It also supports conventional
short-circuit studies without reference to any particular standards.
Short circuit studies provide post fault bus voltages at different busbars in
the network for a fault at any one of the location in the network. These results
are typically given as fault MVA’s, fault currents in kA at different bus bars
and fault contributions from adjacent bus
sections to the fault, on a single line diagram for various operating
conditions. Short circuit studies for minimum fault level condition at the main
switch board may be of interest in relay coordination to check, whether relays
can distinguish between the maximum load currents and minimum fault currents. In
the event, the minimum fault currents in the relays are very close to the
maximum load currents, it may be necessary to suggest voltage restraint for
relays to ensure that the relays will operate only for fault conditions and not
for healthy full load conditions.
The deliverables from the short circuit studies will include the following
Tabular report of conventional short circuit levels at
Tabular reports of Making/Breaking Current levels at all
Report on single line diagrams showing fault levels,
fault kA for both conventional and IEC 60909 type calculations
Recommendations with respect to operating strategy, to limit short circuit levels where needed
General Features of Short Circuit
Fault levels for asymmetrical and symmetrical faults including bolted faults.
IEC standards including 363 and 909.
G74 British standard, a computer algorithm based standard for IEC 909 standard.
IEC 909 standard specified multiplication factors based on hand calculation procedures
and simplifying assumptions.
Short circuit analysis of multiple-islanded systems with solution for each of the
Default flat 1.0 pu positive sequence bus voltage based calculations.
Option to consider pre-fault bus voltages from load flow along with the sequence
impedances for loads.
Automatic one line diagram creation.
Multiple case studies in single execution of the program for different network configurations
and/or different source impedances or ratings.
Automatic generation of reports for all the specified study cases on the single
Induction motor models.
Fault calculations for network with multiple islands with sources in each island.
Detailed system wide post fault bus voltages and flows for specified bus faults
along with impedance seen at each relay locations.
Output contains, detailed phase quantities, sequence quantities of voltages, currents,
driving point impedances, transfer impedances, contribution from sources, and contribution
from adjacent buses.
Results of fault calculations with mutual coupling matches perfectly with published
Equivalent Generator Representation for Power System Analysis