Ship Electrical Short Circuit Current, Breaker Capacity & Busbar Fault Level Tool

Prospective Short-Circuit Current • Busbar Fault MVA • Generator & Motor Contribution • Breaker Breaking & Making Duty • I²t • N-1 Fault Level

Ship Electrical Short Circuit Current, Breaker Capacity & Busbar Fault Level Tool

Screen shipboard AC fault levels against circuit-breaker interrupting and making capacity instead of comparing generator kVA with breaker kA. Simple mode estimates main-bus symmetrical and peak short-circuit duty. Advanced combines generator, transformer/shore and motor contributions through entered fault-path impedance, then checks multiple fault locations, breaker margins, busbar thermal duty and N-1 source configurations.

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Nine inputs for a fast main-bus breaker-duty screen.Use generator subtransient reactance and breaker nameplate data where available. This is a prospective-fault screening calculation, not a protection-coordination or arc-flash study.

Fault CurrentInitial symmetrical kA

Fault LevelBusbar short-circuit MVA

Breaker DutyBreaking & making margin

Source & Motor Contribution

Ship bus voltageV line-to-line, 3-phase.

Online generator countIdentical generators online.

Generator rating eachkVA per generator.

Generator Xdʺ / source impedance% on each generator base.

Running motor loadAggregate kW connected to the faulted bus.

Motor fault-current multiple× estimated motor full-load current.

Equivalent source X/R ratioUsed for peak-making-current screening.

Breaker Ratings

Breaker rated breaking capacitykA RMS symmetrical at system voltage.

Breaker rated making capacitykA peak.

System Basis

System voltageV line-to-line.

Frequency

Voltage factor cUser-entered short-circuit voltage factor.

Target breaker capacity margin% above calculated duty.

Default motor PF

Default motor efficiency

AC Source Register

Generator / transformer rows use rating and entered impedance. “Direct kA” rows use an OEM or study-derived initial symmetrical contribution. Quantity is treated as identical units operating in parallel.

Use	Online?	Type	Name	Qty	Rating kVA	Z / Xdʺ %	Direct Ikʺ kA / unit	X/R

Running Motor Contribution Register

Motor short-circuit contribution is screened as entered multiple × calculated full-load current. For a formal marine study, use the motor contribution model required by the applicable standard/class method.

Use	Running?	Name	Qty	Rated kW	PF	Efficiency	Fault × FLA	X/R

Fault Location / Breaker Duty Register

Path R and X are the common impedance from the analyzed source bus to the fault location. Breaker RMS breaking capacity, peak making capacity and busbar short-time withstand are compared with the calculated prospective duty.

Use	Fault location	Path R mΩ	Path X mΩ	Breaker break kA RMS	Breaker make kA peak	Bus Icw kA	Icw duration s	Clearing time s

Study / Protection Checks

Generator Xdʺ / source data verifiedEntered source impedances reflect the intended operating configuration. Motor contribution reviewedLarge running motors and propulsion/auxiliary drives are represented appropriately. Breaker voltage-specific ratings checkedBreaking and making values correspond to the actual system voltage and standard. Busbar short-time withstand checkedIcw rating and duration are based on switchboard documentation. Fault-path impedance checkedCables, busway, transformer and other common impedance are represented where relevant. Protection clearing time verifiedThermal screen uses credible protective-device clearing time. Operating configurations reviewedBus-tie, shore supply and generator combinations that can maximize fault duty are included. Formal coordination study planned / availableThis tool supplements, rather than replaces, approved coordination and class short-circuit documentation.

Engineering boundary: this tool is a screening / planning model. It does not replace a formal IEC 61363-1 marine short-circuit study, IEC 60909 calculation where applicable, class review, breaker time-current coordination, arc-flash assessment or OEM verification. Converter-fed sources can have current-limited behavior that must be entered from manufacturer/study data rather than inferred from rotating-machine reactance.

Technical basis: IEC 61363-1:1998 remains the dedicated IEC procedure for calculating short-circuit currents in unmeshed three-phase marine and offshore AC systems. IEC 60909-0:2026 is the current general IEC short-circuit calculation standard for 50/60 Hz three-phase AC systems. ABS requires protective devices to have breaking capacity not less than the maximum prospective RMS short-circuit current at the point of installation and making capacity adequate for the maximum prospective peak current. The tool therefore treats breaker breaking and making duties separately and keeps project/class limits user-entered.

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