Why low voltage winding of transformer in the inside,and high voltage winding in the outside?

The arrangement of the high and acmotor2.blogspot.com low voltage transformer,it is decided by many factors.But for most of the transformer,low level around the layout in the high voltage winding is put inside.This is mainly from the insulation into consideration.In theory,no matter how high or low voltage windings to decorate,can be variable pressure role.But because the iron core transformer is grounded,due to the single phase generator low voltage winding is close to the core,from the perspective of insulation easy to do.If the high voltage winding is close to the core,is due to the high voltage winding voltage is very high,to meet the insulation requirements,requires very of insulation materials and the insulation of the large distance.Such not only increases the volume of small electric motors the winding,and waste of the insulating material.Moreover,as a result of the transformer voltage regulation is electrical motor to rely on change of the high voltage winding tap,namely change the number of turns,so the high voltage winding is placed in the low voltage winding outside,lead more easily also.