Short-Circuit Study
Calculate fault duties, verify interrupting ratings, and support protection engineering and equipment selection.
What is a Short-Circuit Study?
A short-circuit study calculates fault currents under defined system conditions to verify equipment interrupting capability, equipment withstand limits where applicable, and to support protection coordination and settings decisions. Fault levels often change significantly when adding generation, BESS, or altering transformer configurations.
Short-circuit analysis determines the maximum current that flows when a fault occurs at different locations in the power system. This includes three-phase faults, single-line-to-ground faults, and other fault types as required. The results are used to verify that breakers, switchgear, and other equipment can safely interrupt fault current without damage.
This study is critical for interconnection projects, equipment upgrades, and protection coordination work. Utilities and regulatory bodies require verification that all equipment has adequate interrupting and withstand ratings.
When This Study Is Required
Interconnection of Generators and BESS
New generation sources change fault contribution
New Substations & Switchgear
Breaker replacements and equipment ratings verification
Protection Coordination Projects
Relay settings require accurate fault current data
Utility/RTO Studies & Upgrades
Compliance support and system modification reviews
What eGridSync Delivers
Fault duty calculations (3-phase, single-line-to-ground, etc. as required)
Breaker interrupting rating verification and duty margin reporting
Source contribution breakdown (utility + generation/BESS)
Bus fault level summary tables (before/after project)
Equipment impact summary (switchgear/breakers/transformers)
Coordination study inputs and support deliverables
Recommendations (breaker upgrades, impedance solutions, topology changes)
Final report with assumptions and model notes
Inputs Required (Data Request Checklist)
| Item | Examples | Why Required |
|---|---|---|
| One-line diagram & equipment list | Breakers, switchgear, transformers | Identify study nodes and ratings |
| Utility source data | Thevenin equivalent, SC MVA, X/R | Set upstream fault strength |
| Generator/BESS contribution | Subtransient Xd", inverter fault limits | Accurate fault current contributions |
| Transformer data | MVA, %Z, winding config | Drives fault levels and distribution |
| Protection context | CT/PT, relay types (optional) | Supports coordination tie-in |
| Existing models/reports | Prior SC report or case | Baseline and faster validation |
Assumptions & Typical Settings
Fault Types & Locations
Per scope and utility requirements
System Configuration
Normal vs alternate topologies documented
Temperature/Rating Assumptions
Consistent with client/utility requirements
Equipment Data
Accurate impedances and fault contribution limits
Outputs & Reporting
Fault Duty Tables by Bus
3-phase and ground fault currents at each bus
Breaker Duty Comparison & Margin
Calculated duty vs. nameplate rating with margin analysis
"Before/After" Fault Level Changes
Impact of new equipment on system fault levels
Recommendations & Next Steps
Equipment upgrades, mitigation strategies, action items
Common Issues Identified
Breaker Duties Exceeding Ratings
After interconnection, existing breakers may exceed nameplate interrupting capacity requiring replacement
Underestimated Fault Contributions
Missing model limits or incorrect impedance data causing unrealistic fault currents
Model/Equipment Misalignment
Short-circuit model does not reflect actual equipment configuration leading to incorrect results
Inadequate Source Data
Incomplete or outdated utility source impedance affecting accuracy of fault calculations
Frequently Asked Questions
Why can PV/BESS increase fault duty?
Inverters and transformers contribute to fault current; changes depend on control limits and system strength.
What is breaker duty?
The fault current a breaker must interrupt safely.
Do I need both 3Ø and SLG faults?
Usually yes, depending on grounding and utility requirements.
Can you support equipment selection?
Yes—duty margins help justify upgrades.
How does this connect to coordination?
Coordination requires accurate fault currents for relay timing/selectivity.
What's the most important input?
Accurate utility source data and breaker ratings.
What if utility won't provide Thevenin?
We use available short-circuit levels or utility-provided equivalents if possible.
Will you provide "before/after"?
Yes—very helpful for interconnection justification.
Do you update the model if design changes?
Yes—reruns can be done when topology/equipment updates occur.
Does this help PRC work?
It supports protection coordination and settings evidence where needed.
Ready for Short-Circuit Analysis?
For fault duty calculations and equipment rating verification, contact eGridSync.