# 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.
Phase

Transformer rating

Primary voltage (V)

Secondary voltage (V)

## 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 (Vp): The rated voltage of the primary winding. In a step down transformer, this will be the higher voltage.
• Secondary voltage (Vs): The rated voltage of the secondary voltage. In a tep down transformer, this will be the lower voltage.

## How to calculate transformer primary full load current?

The primary winding full load current Ip is calculated as:

$$I_{p}= \dfrac{S}{\sqrt{3} V_{p}}$$

Where,

• S is the transformer rating.
• Vp is the primary winding voltage.

## How to calculate transformer secondary full load current?

The secondary winding full load current Is is calculated as:

$$I_{s}= \dfrac{S}{\sqrt{3} V_{s}}$$

Where,
• S is the transformer rating.
• Vs is the secondary winding voltage.

## How to calculate transformer turns ratio?

The transformer turns ratio n is calculated as:

$$n = \dfrac{ V_{p} }{ V_{s} }$$, Where,

• Vp is the primary winding voltage.
• Vs is the secondary winding voltage.

## 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.

$$n = \dfrac{11000}{420}$$

$$n = 26.2$$