Transformer Primary Current Calculator

Calculate transformer primary current using KVA rating and primary voltage

Transformer Primary Current Calculator

Compliant with IEEE C57.12.00 Standards

Results:

Primary Current (IP): 0.00 A

Ideal Primary Current: 0.00 A

Power Rating: 0.00 kVA

Transformer Full Load Current Calculator
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How to Use Transformer Primary Current Calculator

Single Phase Transformer

  1. Select "Single Phase" transformer type
  2. Enter the KVA rating of the transformer
  3. Enter primary voltage (VP) in volts
  4. Set transformer efficiency (typically 95-99%)
  5. Click "Calculate" to get primary current

Formula Used: IP = KVA Rating / VP

Three Phase Transformer

  1. Select "Three Phase" transformer type
  2. Enter the KVA rating of the transformer
  3. Enter primary line-to-line voltage (VP)
  4. Set transformer efficiency (typically 96-99%)
  5. Click "Calculate" to get primary current

Formula Used: IP = KVA Rating / (√3 × VP)

Important Notes

  • KVA rating is the transformer's apparent power capacity
  • Use line-to-line voltage for three phase transformers
  • Higher primary voltage results in lower primary current
  • Efficiency affects the actual primary current drawn from supply
  • Results show both ideal and actual primary current

How to Calculate Transformer Primary Current

Single Phase Formula

Primary Current Formula:

IP = KVA Rating / VP

With Efficiency:

IP (actual) = KVA Rating / (VP × η)

Where:

  • IP = Primary current (A)
  • KVA = Transformer rating (kVA)
  • VP = Primary voltage (V)
  • η = Efficiency (decimal)

Three Phase Formula

Primary Current Formula:

IP = KVA Rating / (√3 × VP)

With Efficiency:

IP (actual) = KVA Rating / (√3 × VP × η)

Where √3 = 1.732 for three phase calculations

  • Use line-to-line voltage for VP
  • Result gives line current value
  • √3 factor accounts for three phase relationship

Real-Life Calculation Example

Three Phase Transformer Example:

Given:

• Transformer Rating: 100 kVA

• Primary Voltage (VP): 11,000V (line-to-line)

• Efficiency: 98% (0.98)

Step 1: Calculate Ideal Primary Current

IP (ideal) = KVA Rating / (√3 × VP)

IP (ideal) = 100 / (1.732 × 11)

IP (ideal) = 100 / 19.052 = 5.25A

Step 2: Calculate Actual Primary Current

IP (actual) = KVA Rating / (√3 × VP × η)

IP (actual) = 100 / (1.732 × 11 × 0.98)

IP (actual) = 100 / 18.671 = 5.36A

Result: Primary Current = 5.36A (actual), 5.25A (ideal)

Primary Current Formulas

Single Phase:
IP = KVA Rating / VP

Three Phase:
IP = KVA Rating / (√3 × VP)

With Efficiency:
IP (actual) = IP (ideal) / η

Power Relationship:
P = VP × IP (Single Phase)
P = √3 × VP × IP (Three Phase)

Key Principles

  • Primary current is inversely proportional to primary voltage
  • Higher KVA rating means higher primary current
  • Three phase transformers use √3 factor (1.732)
  • Efficiency affects actual current drawn from supply
  • Lower efficiency means higher primary current
  • Primary current determines supply cable sizing

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