1. What is Primary Current?

The primary current (I_primary) is the current flowing in the primary winding of a three-phase transformer. It's determined by the transformer's power rating (kVA) and the primary voltage.

2. How Does the Calculator Work?

The calculator uses the primary current formula:

Where:

• \( I_{primary} \) — Primary current (amps)
• \( kVA \) — Transformer power rating (kilovolt-amps)
• \( V_{primary} \) — Primary voltage (volts)
• \( \sqrt{3} \) — Constant for three-phase systems (≈1.732)

Explanation: The formula converts kVA to VA (×1000) and divides by the primary phase-to-phase voltage adjusted for three-phase systems.

3. Importance of Primary Current Calculation

Details: Knowing the primary current is essential for selecting proper conductor sizes, protective devices, and ensuring the transformer operates within its rated capacity.

4. Using the Calculator

Tips: Enter the transformer's kVA rating and primary voltage in volts. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Is this formula only for three-phase transformers?
A: Yes, this specific formula is for three-phase transformers. Single-phase transformers use a different formula without the √3 factor.

Q2: What are typical primary current values?
A: Primary current varies greatly depending on transformer size and voltage. A 1000kVA transformer at 11kV would have about 52.5A primary current.

Q3: Why is the √3 factor used?
A: The √3 accounts for the phase difference in three-phase systems when converting between line-to-line voltage and phase current.

Q4: Does this consider transformer efficiency?
A: No, this is the ideal current calculation. Actual current may be slightly higher due to transformer losses.

Q5: Can I use this for secondary current calculation?
A: The same formula applies to secondary current if you use the secondary voltage instead of primary voltage.