measuring insulation resistance to a wye-wye padmounted transformer

[danicano]

I have a 2000 KVA padmounted transformer. Volt pri 13.8KV Y. Volt sec 480/277 Y.
On the data plate there is a link between the primary winding and the secondary winding with the text "Removable Link".

Bushing H0 and X0 appear as joined and it is common between them, located in the cabinet on the secondary side (low voltage). And on the outside comes a copper tape to join it to the metal of the tank.


What should be the practice to measure the insulation of the windings to ground?

Is it necessary to remove this internal connection inside the transformer tank that is full of oil?
Thanks

dacanoro

 

[davidbeach]

Remove the link for transformer testing. Otherwise leave it connected.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[prc]

You can measure H-G and L-G IR values without removing the link. The only value that you cannot check is H-L values. For health monitoring, I think it is not that important. That may be the reason Westinghouse kept that link under oil.

 

[stevenal]

With the link in place, you are not really measuring H-G and L-G separately. You can still find problems and have a value to trend.

 

[davidbeach]

Missed the bit about the link being under oil...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[prc]

Can you explain a bit more. I think it will be correct. You will be grounding the tank and core to the ground. Then measure (H+X+H0)-G; (H+H0)-G;(X+X0)-G. Short H0X0 terminal to the shorted line terminals of H or X as required.