Transformer Short Circuit Current Calculator
Calculate fault currents for power system protection and equipment sizing
Transformer Short Circuit Calculator
Compliant with IEEE C57.12.00 Standards
Results:
Secondary Short Circuit Current: 0.00 A
Secondary Short Circuit kA: 0.00 kA
Primary Referred Current: 0.00 A
Through Fault Current: N/A
X/R Ratio: N/A
How to Use Transformer Short Circuit Current Calculator
Three Phase Transformers
- Select "Three Phase" transformer type
- Enter transformer kVA rating
- Input primary voltage (line-to-line)
- Enter secondary voltage (line-to-line)
- Provide impedance percentage from nameplate
- Optionally add primary fault current for through fault analysis
Single Phase Transformers
- Select "Single Phase" transformer type
- Enter transformer kVA rating
- Input primary voltage
- Enter secondary voltage
- Provide impedance percentage
- Review calculated fault currents
Important Notes
- Impedance percentage is found on transformer nameplate
- Use line-to-line voltages for three-phase systems
- Results assume infinite primary source unless specified
- Consider safety factors for equipment selection
- Verify calculations with system studies
How to Calculate Transformer Short Circuit Current
Three Phase Calculation
Step 1: Calculate base current
I_base = kVA × 1000 / (√3 × V_secondary)
Step 2: Calculate short circuit current
I_sc = I_base / (Z% / 100)
Step 3: Calculate primary referred current
I_primary = I_sc × (V_secondary / V_primary)
Single Phase Calculation
Step 1: Calculate base current
I_base = kVA × 1000 / V_secondary
Step 2: Calculate short circuit current
I_sc = I_base / (Z% / 100)
Step 3: Calculate primary referred current
I_primary = I_sc × (V_secondary / V_primary)
Real Life Calculation Example
Given: 1000 kVA, 11kV/400V, 3-phase transformer, Z% = 4.5%
Step 1: Calculate base current
I_base = 1000 × 1000 / (√3 × 400) = 1000000 / 692.82 = 1443.38 A
Step 2: Calculate short circuit current
I_sc = 1443.38 / (4.5 / 100) = 1443.38 / 0.045 = 32,075 A
Step 3: Convert to kA
I_sc = 32,075 A = 32.08 kA
Step 4: Primary referred current
I_primary = 32,075 × (400 / 11000) = 1,166.4 A
Result: Secondary fault current = 32.08 kA
Calculation Formulas
Three Phase:
I_sc = (kVA × 1000) / (√3 × V × Z%/100)
Single Phase:
I_sc = (kVA × 1000) / (V × Z%/100)
Primary Referred:
I_primary = I_sc × (V_sec / V_pri)
Through Fault:
I_through = I_primary_fault × (V_pri / V_sec)
Safety Considerations
- Always apply appropriate safety factors
- Consider asymmetrical fault currents
- Account for system impedance variations
- Verify with detailed system studies
- Consider temperature effects on impedance
- Review equipment interrupting capacity