Grounding current for transformer tank

[mfmsheri]

Hi,

goodwill for every body,

the question about a Generator Step-Up Transformer (15Kv/132Kv) (185 MVA) ,the tank of this transformer is grounded by two points, after measured one was 78A and the other was 44A, that mean the grounding current will be more than 120A.

this's value for grounding current is acceptable or not?

 

[7anoter4]

In my opinion, a third harmonic current generated by generator could flow through grounding conductor. In this case 1.7% of the rated it could be reasonable.
The current flowing through grounding conductor could be-also- from high voltage side as capacitive current from the high voltage overhead line- mainly, if the transformer neutral is not grounded.

 

[prc]

The current values noted are perfectly OK. The maximum that I noted is about 800 A each in a rectifier transformer. Then one of the earths were disconnected and the current value came down to about 400 A. These high grounding currents are seen mainly in transformers with a LV winding with high currents. This current seems to be due to potential difference generated between the tank and grounding grid from the winding leakage flux creating a circulating current in tank.