1. What is the 3 Phase Transformer Fuse Calculation?

The 3 Phase Transformer Fuse calculation determines the appropriate fuse size for protecting a three-phase transformer, accounting for inrush current with a 1.25 multiplier. Proper fuse sizing is critical for both protection and operational reliability.

2. How Does the Calculator Work?

The calculator uses the 3 phase transformer fuse formula:

Where:

• \( kVA \) — Transformer kilovolt-amp rating
• \( V \) — Line voltage (volts)
• \( \sqrt{3} \) — Constant for three-phase calculations (≈1.732)
• 1.25 — Multiplier for inrush current protection

Explanation: The formula first calculates the full-load current of the transformer, then applies a 25% safety factor to accommodate inrush current during startup.

3. Importance of Proper Fuse Sizing

Details: Correct fuse sizing ensures protection against short circuits while allowing for normal operation and temporary overloads. Undersized fuses may nuisance trip, while oversized fuses may not provide adequate protection.

4. Using the Calculator

Tips: Enter the transformer's kVA rating and system voltage. The calculator will determine the recommended fuse size with built-in safety factor for inrush current.

5. Frequently Asked Questions (FAQ)

Q1: Why is there a 1.25 multiplier in the formula?
A: The 1.25 factor accounts for transformer inrush current, which can be 8-12 times the full-load current for a brief period during startup.

Q2: Can I use this for single-phase transformers?
A: No, this calculator is specifically for three-phase transformers. Single-phase calculations use a different formula without the √3 factor.

Q3: What if my calculated fuse size isn't a standard rating?
A: Always round up to the next standard fuse size. Common standard sizes include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 amps, etc.

Q4: Does this account for ambient temperature or enclosure factors?
A: No, this is a basic calculation. Additional derating may be needed for high ambient temperatures or enclosed spaces.

Q5: Should I consider other protection devices?
A: For comprehensive protection, consider using circuit breakers with appropriate trip characteristics or dual-element time-delay fuses.