Transformer Voltage Drop Calculator
Calculate voltage loss instantly using our transformer voltage drop calculator. Get accurate results for better system efficiency and safe electrical design. Ideal for engineers, electricians, and students working with transformers.
Transformer Voltage Drop Tool
How to Use Transformer Voltage Drop Calculator
Follow these simple steps to use the transformer voltage drop calculator:
- Enter Primary Voltage: Input the transformer’s primary side voltage (e.g., 11kV, 400V).
- Enter Secondary Voltage: Add the rated secondary voltage of the transformer.
- Input Load Current: Enter the actual load current in amperes (A).
- Enter Transformer Impedance (%): Use the nameplate impedance value (typically 4%–10%).
- Select Phase Type: Choose single-phase or three-phase system.
- Click Calculate: The calculator instantly shows voltage drop and percentage drop.
Tip: Always use accurate nameplate data for best results.
How to Calculate Transformer Voltage Drop (Step-by-Step)
Transformer voltage drop depends on impedance and load.
Formula
For simplified calculation:
Step-by-Step Example
Given:
Transformer Rating = 100 kVA
Secondary Voltage = 400V
Load Current = 120 A
Impedance = 5%
Step 1: Calculate Full Load Current
Full Load Current = (kVA × 1000) / (√3 × Voltage)
Full Load Current = (100 × 1000) / (1.732 × 400)
Full Load Current = 144.3 A
Step 2: Calculate % Voltage Drop
% Voltage Drop = (120 / 144.3) × 5
% Voltage Drop ≈ 4.16%
Step 3: Calculate Actual Voltage Drop
Voltage Drop = 400 × (4.16 / 100)
Voltage Drop ≈ 16.64 V
Final Answer:
Transformer voltage drop = 16.64V (4.16%)
Transformer Voltage Drop Conversion Chart
| Load % | Impedance % | Voltage Drop % |
|---|---|---|
| 25% | 4% | 1.0% |
| 50% | 4% | 2.0% |
| 75% | 4% | 3.0% |
| 100% | 4% | 4.0% |
| 25% | 5% | 1.25% |
| 50% | 5% | 2.5% |
| 75% | 5% | 3.75% |
| 100% | 5% | 5.0% |
| 25% | 6% | 1.5% |
| 50% | 6% | 3.0% |
| 75% | 6% | 4.5% |
| 100% | 6% | 6.0% |
Use this chart for quick estimation without calculation.
FAQs – Transformer Voltage Drop Calculator
Transformer voltage drop is the reduction in output voltage due to load and internal impedance.
It affects system efficiency, equipment performance, and voltage stability.
Typically, 2%–5% is acceptable depending on standards and application.
Yes. Higher load current increases voltage drop proportionally.
Higher impedance results in higher voltage drop.
Yes. Use lower impedance transformers or reduce load current.
Yes. Three-phase systems use √3 in calculations, making results slightly different.
Yes, if you input correct transformer ratings and load data.
IEC and NEC recommend keeping voltage drop within safe limits for system reliability.
It is critical in power distribution, industrial systems, and sensitive equipment setups.