Transformer Impedance Calculator

Calculate transformer impedance using Z = (Vp/Ip) × (100/%) with automatic current calculation

Transformer Impedance Calculator

Using Formula: Z = (Vp/Ip) × (100/%) | Ip = kVA × 1000 / (√3 × Vp)

Results:

Transformer Rating: 0 kVA

Primary Current (Ip): 0 A

Impedance (Z): 0.00 Ω

Primary Voltage (Vp): 0 V

Impedance Percentage: 0 %

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How to Use the Transformer Impedance Calculator

Step 1: Enter Transformer Rating

  1. Input the transformer rating in kVA
  2. Common ratings: 100, 250, 500, 1000, 1500, 2000 kVA
  3. Large power transformers: 10MVA, 25MVA, 100MVA
  4. Distribution transformers: 25kVA, 50kVA, 100kVA

Step 2: Enter Primary Voltage

  1. Input the primary voltage (Vp) in volts
  2. High voltage: 11kV, 33kV, 132kV, 220kV
  3. Medium voltage: 6.6kV, 11kV, 22kV
  4. Low voltage: 415V, 480V, 600V, 1000V
  5. Primary current will be calculated automatically

Step 3: Enter Impedance Percentage

  1. Input the impedance percentage from nameplate
  2. Power transformers: 8% to 15%
  3. Distribution transformers: 4% to 8%
  4. Small transformers: 2% to 6%
  5. Click "Calculate Impedance" to get result

Transformer Impedance Theory

What is Transformer Impedance?

Transformer impedance is the total opposition to current flow, combining resistance and reactance of the transformer windings and core.

  • Expressed in ohms (Ω) or as percentage (%)
  • Determines voltage drop under load
  • Critical for short circuit calculations
  • Affects parallel operation of transformers

Applications

  • Power system fault analysis
  • Protection relay coordination
  • Voltage regulation studies
  • Load flow analysis
  • Transformer parallel operation

Formulas Used:

Primary Current: Ip = kVA × 1000 / (√3 × Vp)

Impedance: Z = (Vp/Ip) × (100/%)

Where:

Z = Impedance in Ohms (Ω)

Vp = Primary Voltage in Volts (V)

Ip = Primary Current in Amperes (A)

% = Impedance Percentage (%)

How to Calculate Transformer Impedance

Primary Current Formula:
Ip = kVA × 1000 / (√3 × Vp)

Impedance Formula:
Z = (Vp/Ip) × (100/%)

Where:
kVA = Transformer Rating
Vp = Primary Voltage (V)
Ip = Primary Current (A)
% = Impedance Percentage

Real-Life Calculation Example

Given: 1000 kVA, 11kV/415V transformer with 5.5% impedance

Step 1: Calculate Primary Current

Using formula: Ip = kVA × 1000 / (√3 × Vp)

Given: kVA = 1000, Vp = 11,000V

Ip = 1000 × 1000 / (√3 × 11,000)

Ip = 1,000,000 / (1.732 × 11,000)

Ip = 1,000,000 / 19,052

Ip = 52.49 A

Step 2: Calculate Transformer Impedance

Using formula: Z = (Vp/Ip) × (100/%)

Given: Vp = 11,000V, Ip = 52.49A, % = 5.5%

Z = (11,000/52.49) × (100/5.5)

Z = 209.54 × 18.18

Z = 3,809.45 Ω

Step 3: Verification

Voltage drop at full load:

Drop = Ip × Z × (%/100) = 52.49 × 3,809.45 × (5.5/100)

Drop = 10,999.97 V ≈ 11,000V ✓

Percentage = (11,000/11,000) × 100 = 100% ✓

Final Result:

Primary Current = 52.49 A

Transformer Impedance = 3,809.45 Ω

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