Online calculator for transformer primary and secondary rating current .
| Primary Rating Current | ||
| Secondary Rating Current |
How to determine transformer current rating
Transformer primary and secondary current rating calculated by below formulas
1. Three Phase Transformer:
2. Single Phase Transformer:
Where:
- S : Transformer Apparent kVA
- V : Line voltage of primary or secondary winding in kV
- I : Ampere rating of primary or secondary respectively in A
Transformer inrush current
When a transformer is energized, primary side will experience a inrush current prior to reach transformer stability operating current. Inrush current is due to a certain amount of residual flux remains in the iron core due to the properties of the magnetic core material.
Inrush current in a dry and liquid filled transformers is equivalent to about 12, or even as high as 18, times rated current with a duration of 0.1s (Source: IEEE 242 Buff Book).
Example of a transformer nameplate with current rating
Transformer primary current rating from nameplate is 54.1A which is same with result from above calculator.
