1. What is Short Circuit Calculation of Transformer?

Definition: This calculator determines the short circuit current a transformer can deliver based on its power rating, voltage, and impedance percentage.

Purpose: It helps electrical engineers and technicians assess potential fault currents for proper protective device selection and system design.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( I_{sc} \) — Short circuit current (amperes)
• \( S \) — Transformer power rating (volt-amperes)
• \( V \) — System voltage (volts)
• \( \%Z \) — Transformer impedance percentage

Explanation: The transformer's full load current is divided by its impedance percentage (expressed as a decimal) to determine the short circuit current.

3. Importance of Short Circuit Calculation

Details: Accurate short circuit calculations ensure proper sizing of circuit breakers, fuses, and other protective devices to safely interrupt fault currents.

4. Using the Calculator

Tips: Enter the transformer power in VA, system voltage in volts, and impedance percentage (default 5%). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is typical transformer impedance?
A: Common values range from 2-7% for distribution transformers, with 5% being typical for many applications.

Q2: Why is short circuit current higher than normal current?
A: During a short circuit, the only limiting factor is the transformer's impedance, allowing much higher current flow.

Q3: Should I use primary or secondary voltage?
A: Use the voltage of the side where you want to calculate the short circuit current.

Q4: How does this relate to arc flash calculations?
A: Short circuit current is a key input for determining incident energy in arc flash studies.

Q5: What safety margin should I add?
A: Consider adding 10-20% to account for system contributions and future growth.