Wont the above steps help reduce the inetrwinding capacitance ?

Hallo Raghunathan,

sorry for being late, but I was busy...

Well, this interwinding capacitance cannot be decreased very much. The standard safety transformer shows minimal interwinding capacitance by design, because both windings sit on different frames. By this, both windings are not laying directly on each other, but are separated a bit. This gives minimum interwinding capacitance.
The stuff with the shield winding was widely used in the past. But not in order to increase shielding, but because manufacturer didn't trust their isolation materia very much. They thought, that if the barrier is damaged by some overvoltage condition, there's at least this shield, which shunts dangerous potentials to protection earth. Shield winding was mainly used with transformers, where by design both windings are bent directly on each other. This is different to the safety transformer, which uses two separated frames.
The shield winding with standard transformer does indeed improve shielding, but mostly it will not give better performance than standard safety transformer having no shield at all.
Ring core transformers are very bad referring to interwinding capacitance. Here, a shield winding can be of high benefit. Shielded ring core mains transformers are sometimes used with High End audio amplifiers.

There's a very easy methode to prevent common mode noise from penetrating your system. Even with safety class II power supply, you can shunt common mode noise to protection earth by the following circuit:



Keep in mind, that your power supply still must fullfill safety class II requirements, means providing safety by double or enhanced isolation. 'Earth' here is not the 'protection earth', but a 'functional earth'. This means, that especially mains transformer must still be a safety transformer.

One further advantage of this circuit is, that diodes are now protected against heavy overvoltage spikes coming from primary side. Think about lightnings...

Also can you post some links for the kind of ferrite beads that you had recommended in your reply?

Have a look at

http://www.we-online.com

They do have many of them. But there many other manufacturers very well, which have them too. It's not so important, what kind of ferrite choke you use. Important is, that you USE them, and at each single cable!
At 1GHz impedance should be well above 100Ohm, at 1MHz impedance should be above 10Ohm.

Kai