Understanding short-circuit analysis

Short-circuit analysis calculates fault currents when an electrical fault (short circuit) occurs in your system. These calculations determine the interrupting capacity required for protection devices and verify equipment ratings.

What short-circuit calculates

Fault current types:

• Initial symmetrical short-circuit current (Ik'')
• Peak short-circuit current (Ip) - maximum instantaneous value
• Breaking current (Ib) - RMS value at circuit breaker opening
• Thermal equivalent short-circuit current (Ith) - for thermal calculations

For each bus:

• Three-phase fault current
• Phase-to-phase fault current
• Single-phase-to-ground fault current
• Fault MVA at each point

Equipment verification:

• Breaker interrupting capacity requirements
• Bus bracing requirements
• Cable short-circuit withstand
• Protective device coordination

Fault current types

Initial short-circuit current (Ik''):

• First half-cycle RMS current
• Subtransient component
• Highest magnitude
• Used for peak current calculation

Peak current (Ip):

• Maximum instantaneous value
• Includes DC offset component
• Determines mechanical forces on busbars
• Formula: Ip = κ × √2 × Ik'' (κ depends on X/R ratio)

Breaking current (Ib):

• Current when breaker contacts separate
• Typically 3-5 cycles after fault
• Lower than Ik'' due to decay
• Determines breaker rating

Thermal current (Ith):

• Equivalent steady-state current for heating
• Used for cable short-circuit withstand
• Calculated from fault duration and current magnitude

Why short-circuit analysis matters

Protection device selection:

• Breakers must have interrupting capacity ≥ fault current
• Undersized breakers cannot clear faults safely
• May explode or fail to interrupt

Equipment rating verification:

• Buses, switchgear must withstand fault forces
• Cables must handle thermal stress during fault
• Transformers must withstand through-faults

Coordination:

• Upstream devices must remain closed while downstream operates
• Requires fault current at each point
• Time-current curves based on fault current

Safety:

• Arc flash energy depends on fault current
• Higher fault current = higher incident energy
• Personnel protection requirements

PandaPower calculation method

ekx uses PandaPower short-circuit calculations following IEC 60909 standard:

1. Convert network to impedance model
2. Calculate source impedances
3. Apply correction factors
4. Solve fault equations for each bus
5. Extract currents and voltages

Standards support:

• IEC 60909 (international)
• ANSI/IEEE standards (future)

Prerequisites for analysis

Required components:

• At least one source (utility feed or generator)
• Complete network topology
• All component impedances specified
• Voltage ratings for all buses

Source impedance:

• Utility short-circuit MVA and X/R ratio
• Generator subtransient reactance (X''d)
• Transformer impedance percentage

Missing data causes:

• Calculation failure
• Incorrect results
• "Insufficient data" errors

Related topics

• Fault types - Three-phase, phase-to-phase, single-phase faults
• Running analysis - How to execute short-circuit calculation
• Protection devices - Interrupting capacity requirements