Answer / guest

Stepdown transformer(HT/LT) generaly used for distribution purpose so secondary side star is necessary and to increase voltage ratio primary side delta is necessary ie. in delta we get line voltage which is 1.732 time of phase voltage (star voltag) therefore less turn required in secondary side.

Answer / siddhartha agrawal

Generally HT side there is only three phase available while
LT side we require neutral. So we connect LT side Star
connection to use phase to phase voltage (415 volt) and
phase to neutral voltage- single phase load (240-220volt).

Generally HT side there is only 3 wire to reduce the cost of
transmission wire cost.

Answer / ap

we use delta connection in primary side (HT side) because if any fault current occurs it circulates in primary only and is not transmitted to secondary. Thus secondary is free of fault current.

Answer / bikki

In HT transformer, the primary side has less voltage stress since it is a step up transformer. But the voltage on secondary side will be high and hence the stress will be also high.As a result, the winding insulation requirement will cost a lot if the connection was Delta on secondary side;because in delta phase voltage=line voltage.
But if the secondary connection is star, then phase voltage will be Line voltage/(sqrt(3) which means the winding has to withstand less voltage stress and hence less insulation is required.Hence lesser cost.

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