Short-Circuit Study
We calculate three-phase and single-phase fault current levels at every bus of the facility, check equipment withstand and breaking capacity against them, and deliver the results as the input of the protection coordination and arc flash studies.
Which questions does this study answer?
The short-circuit study is the foundation of power systems work: every later layer rests on its results.
Do my devices withstand the fault current?
The short-circuit withstand and breaking capacities of switchgear, busbars, cables and breakers are compared with the calculated maximum fault currents.
How do levels change when the plant or grid changes?
Changes such as a new transformer, generator, motor load or a solar/BESS connection are added to the model as scenarios and the fault current contributions are compared.
Is the minimum fault current enough for protection?
Maximum and minimum fault scenarios are calculated together; at the minimum level, protection device sensitivity is noted for the coordination study.
Which other studies use the results?
The bus fault currents are the direct input of the protection coordination and arc flash studies.
Required data
The more complete the data, the more reliable the model; missing items are listed at the start of the study.
- Single-line diagram
- Short-circuit power at the grid connection point (as notified by the utility)
- Transformer, generator, motor and cable data (rating, impedance, length)
- Existing protection device information
- Planned changes (new transformer, solar, BESS, motor)
Working steps
The steps are sequential: the output of each is the input of the next.
01
Data collection and single-line verification
Data is collected; inconsistencies between the single-line diagram and equipment data are flagged.
02
Model setup
The grid, transformer, cable, motor and generator contributions are built in a single power system model in ETAP.
03
Maximum and minimum fault scenarios
Three-phase and single-phase fault currents are calculated for every bus under maximum and minimum operating conditions.
04
Equipment check
The calculated levels are compared with equipment withstand and breaking capacity; items that fall short are flagged.
05
Reporting
Results are delivered, document-controlled, together with their assumptions and limitations.
Reference standard
The calculation method rests on the framework below. It is a reference framework, not a certification or accreditation statement.
- IEC 60909
- Short-circuit currents in three-phase a.c. systems
Calculation software: ETAP
Delivered documents
- Bus-by-bus fault current table (maximum and minimum)
- Equipment withstand and breaking capacity check table
- Statement of assumptions and limitations
- Document control record (prepared by / checked by / approved by, revision)
Scope and limits
- Results depend on the data taken from the facility and the grid short-circuit power notified by the utility; if the data changes, the study must be updated.
- The calculation method is limited to IEC 60909; transient (EMTP) analyses are outside this scope.
- The study is an engineering analysis; equipment replacement and field implementation are a separate scope.
A short-circuit study is not by itself a protection setting proposal; setting proposals are the subject of the protection coordination study.
Short-circuit study for your facility
Let us start from your single-line diagram and clarify the scope and the data needed together.
Request a technical pre-assessment