Dc to primary winding of transformer it will be burnt.but if given to field winding of syn. motor and armature winding of dc motor they are safe, why?

DC voltage provided to primary winding of transformer will cause it to overheat due to absence of sinusoidal wave produced like in AC voltage. Then DC voltage could cause steady state high currents in the coils causing high winding loss in heating and high flux density in the core as hysteresis loss increased to iron core heating.

In motor once DC is supplied and then motor turns, it is converted back to AC as sinusiodal waves due to the action of rotation then overheating is prevented with rated normal parameters.