Usually, the electrical transformer is used to either step up or step down the voltage. It hardly does anything to minimize the crossing of noise or transients from primer to secondary.
Circuit impedances can be by using a transformer to reduce short circuit current or to insulate between two systems.
Except for autotransformers in any transformers, there is no directs connection between primary and secondary winding only magnetic flux connects the windings.
Only a basic separation exists between primary and secondary.
Separation transformer having only a physically separated primary and secondary.
A certain level of protection against electrical shock is provided by insulations between the primary and secondary windings.
Increasing the insulations between the primary and secondary windings a step ahead, an isolation transformer is formed.
The insulations between the two windings give a protection level of double insulations against shock.
In case of contact with the exposed conductive part and the line parts simultaneously this separations minimizes the risk.