Transformer Earth Shield

How tiny is this transformer?

Sorry.... It's a 3 MVA, 11/1.7/1.7 kV, Dyd

And it's wired with foil-shielded cable?

Yes

Your transformer is D y D = delta / star+delta.

First, Shield is used to take out the 3rd harmonics currents from the system.

3rd harmonics will be eliminated in Star winding with shield.

Delta winding does not require shield to nullify the harmonics.

In your specific case, if two shields are joined internally, & brought out & separate earth given to shield, in my opinion, effect will be same as explained above. No harm.

Thanks Potter, but if you said the Delta winding does not require shield, then it should be only one shield in the transformer? Because they specifically said they provide two shield in the secondary.

And what is the difference if the connect the shield together and earth it or earth them separately?

According my opinion, a shield is a kind of cupper foil that is placed between the windings.

A connection lead to the shield is brought outside the transformer.

Is it not possible that the shields are used for

1) to minimise the capacitive coupling between the two winding placed aside?

the higher harmonic currents will flow between the winding and the shield and will not affect the other winding.

2) in case of a break down of the transformer, there will be no electrical connection between primary and secondary winding. There will always be a short cut to earth.