The isolation transformers used for commercial purposes have one leg of the secondary coil connected to the ground. This forms a new neutral that eliminates common mode noise and differential ground noise.
Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass. They also block interference caused by ground loops.
When more than one shielded isolation transformer is installed between the source and the load, this is referred to as “cascading” and vastly improves power quality.
The Ultra Isolation transformers with electrostatic shields are used to protect sophisticated/expensive electrical or electronic equipment. Isolation transformers are also used in the medical industry, to protect patients hooked up to monitoring instruments that are powered by utility mains.
Learn more about Isolation transformer.