1. What is Transformer Short-Circuit Current?

The transformer short-circuit current is the maximum current that would flow if a bolted fault (zero impedance) occurred at the transformer secondary terminals. This value is critical for protective device coordination and equipment ratings.

2. How Does the Calculator Work?

The calculator uses the transformer short-circuit current formula:

Where:

• \( I_{sc} \) — Short-circuit current (Amps)
• \( kVA \) — Transformer rating (kilo-Volt-Amperes)
• \( V \) — Line-to-line voltage (Volts)
• \( Z_{pu} \) — Per unit impedance (decimal)

Explanation: The equation calculates the theoretical maximum current during a fault condition based on transformer characteristics.

3. Importance of Short-Circuit Calculation

Details: Accurate short-circuit current calculation is essential for selecting properly rated protective devices, ensuring equipment withstand ratings, and maintaining system reliability.

4. Using the Calculator

Tips: Enter transformer kVA rating, line-to-line voltage, and impedance percentage. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is typical transformer impedance?
A: Common values range from 2-7% for distribution transformers and up to 10-15% for special applications.

Q2: How does impedance affect fault current?
A: Higher impedance transformers produce lower fault currents, while lower impedance transformers produce higher fault currents.

Q3: Is this calculation conservative?
A: Yes, this calculates the theoretical maximum. Actual fault current may be lower due to system impedance.

Q4: What about single-phase transformers?
A: For single-phase, use I_sc = (kVA × 1000) / (V × Z_pu), removing the √3 factor.

Q5: How does this relate to arc flash calculations?
A: This is the first step in arc flash analysis, which also considers distance, electrode configuration, and clearing time.