# Transformer calculator -full load current and turns ratio

The transformer calculator calculates the primary and secondary full load current, and turns, ratio of a single or 3-phase transformer.## See Also

- Cable sizing calculator AS/NZS 3008
- Maximum demand calculator AS/NZS 300
- Arc Flash Calculator IEEE 1584

## Parameters

**Phase:**Specify the phase arrangement. 1 Phase AC or 3 phase AC.**Transformer rating (S):**The tranformer rating in VA, kVA or MVA.**Primary voltage (V**The rated voltage of the primary winding. In a step down transformer, this will be the higher voltage._{p}):**Secondary voltage (V**The rated voltage of the secondary voltage. In a tep down transformer, this will be the lower voltage._{s}):

## How to calculate transformer primary full load current?

The primary winding full load current **I _{p}** is calculated as:

\( I_{p}= \dfrac{S}{\sqrt{3} V_{p}} \)

Where,

**S**is the transformer rating.**V**is the primary winding voltage._{p}

## How to calculate transformer secondary full load current?

The secondary winding full load current **I _{s}** is calculated as:

\( I_{s}= \dfrac{S}{\sqrt{3} V_{s}} \)

Where,**S**is the transformer rating.**V**is the secondary winding voltage._{s}

## How to calculate transformer turns ratio?

The transformer turns ratio ** n** is calculated as:

\( n = \dfrac{ V_{p} }{ V_{s} } \), Where,

**V**is the primary winding voltage._{p}**V**is the secondary winding voltage._{s}

## Example 1: Calculate transformer full load current

Calculate the secondary full load current of a a 200 kVA, 11 kV to 420 V, step down transformer.

\( I_{s}= \dfrac{200000}{\sqrt{3} \cdot 420} \)

\( I_{s}= 275 \textrm{ A} \)

## Example 2: Calculate transformer turns ratio

Calculate the secondary full load current of a a 200 kVA, 11 kV to 420 V, step down transformer.

\( n = \dfrac{11000}{420} \)

\( n = 26.2 \)