Transformation voltage

you have to take account of voltage drop because the inner resistance of transfermer. so that you can get that values.

High power electrical distributor transformer have not only one fix transformation ratio. Usually they have five or more "points" to select appropiate output voltage for compensating line and internal drops caused by internal and lines resistance and higher current demand. In Argentina when voltage in some larges areas becomes low, any can call to electricity supply company. Operators switch the transformer one or two steps (points) up.

You are talking about the "Tap Changer". What i meant here is that why transformation voltage is some time taken as 11/0.415kv and on other times it is taken as 11/0.433kv.

Dear

1. Power transformer are not designed to give exact fix value of required voltage level at secondary. if primary voltage is varying in some specific range correspondingly to put sec. voltage in specified limit we need tap changing.

2. Consider there are two load, one light & another heavy & input supply is 11000 v. In this case we will go to 415 or 433 volts respectively to adjust tappings.But this may not be hard & fast rule for at all.