Isolation Transformers

Isolation Transformers are transformers which serve to isolate two parts of a circuit. This may be required to ensure that a fault in one part does not affect the other parts of a circuit.

Strictly speaking, all transformers are isolation transformers. The primary and secondary sides are connected through induction and not through conduction. An exception is the autotransformer which cannot provide isolation as its windings are shared.         

Isolation transformers have a transformation ratio of 1:1 as no voltage transformation is involved.         
A grounded shield is usually placed between the primary winding and the secondary winding to prevent any risk of capacitive coupling between the windings. Capacitive couplings can compromise the isolation and provide a linkage between the primary and the secondary circuits. Isolation Transformers are widely used in electronic circuits and in medical instruments.