**Subject :**Electrical Machines I (DC Machines)

**Unit :**Transformer

## Simplified Equivalent Circuit of a Loaded Transformer

**Simplified Equivalent Circuit of a Loaded Transformer**

The no-load current I_{0} of a transformer is small as compared to the rated primary current. Therefore, voltage drops in R_{1} and X_{1 }due to I_{0} are negligible. The equivalent circuit shown in Fig. (7.19) above can, therefore, be simplified by transferring the shunt circuit R_{0} - X_{0} to the input terminals as shown in Fig. (7.20). This modification leads to only slight loss of accuracy.

**(i) Equivalent circuit referred to primary**

If all the secondary quantities are referred to the primary, we get the equivalent circuit of the transformer referred to the primary as shown in Fig. (7.21 (i)). This

further reduces to Fig. (7.21 (ii)). Note that when secondary quantities are referred to primary, resistances/reactances/impedances are divided by K_{2}, voltages are divided by K and currents are multiplied by K.