In our country power generate at l1.5kv. At this voltage current will high and if we transmit power on this voltages line losses will increase because P=I2R. For transmission we use high voltages i.e. 500kv, 220kv, 132kv and 66kv. At these voltages current will low and power losses will also less. For this purpose we use a step up transformer which increase the voltage and decrease the current and at grid station a step down transformer convert again these voltages in 11.5kv. We can’t use these high voltages and the help of step-down transformer we convert voltage as requirement.