Double wound Transformer is a device that transfers energy from one circuit to another by Magnetic coupling.
Apart from its ability to easily convert between different levels of Voltage & current in AC circuits, transformer also provide very useful feature called Isolation. which is the ability to couple one circuit to another without the use of direct wire connection. A very useful application of this is that even if the secondary winding is imposed a high DC voltage (wrt ground) it has no effect on the primary side.
This impressed voltage is often called "Common mode Voltage as it can be seen at more than one pt in the ckt with reference to common ground. This transformer Isolates the common-mode voltage so that it is not impressed on the primary ckt at all. For that matter this could be an AC voltage, even at a different frequency & transformer will isolate it from primary side.
Electrostatic shield can also be provided, between prim & secondly to minimise the effect of capacitive coupling. |