low IR of Power transformer
low IR of Power transformer
(OP)
hello for all
Our step up power Transformer 11kv\20kv 35M va was defected due to low winding Insulation resistance
Now we are swapping a spare transformer to be fixed , but while testing the insulation resistance of 20kv calble it gives:
L1 24 G-ohm
L2 31 G-ohm
L3 1.6 G-ohm
Does it mean cable is not ok?
Our step up power Transformer 11kv\20kv 35M va was defected due to low winding Insulation resistance
Now we are swapping a spare transformer to be fixed , but while testing the insulation resistance of 20kv calble it gives:
L1 24 G-ohm
L2 31 G-ohm
L3 1.6 G-ohm
Does it mean cable is not ok?






RE: low IR of Power transformer
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: low IR of Power transformer
this the only test conducted to condemn the transformer? Generally something like a Power Factor / Dissipation Factor / Tan Delta
test would be conducted to confirm poor IR readings. I am assuming Oil Filled as it was mentioned 35 MVA. If this is a dry transformer, that is another story.
RE: low IR of Power transformer
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: low IR of Power transformer
Surface contamination would be my first guess. If it's a heatshrink or coldshrink type the first easy thing to try is gently wipe the termination with a clean rag soaked in alcohol. Wipe from the lug toward the sheath. Re-test.
After that you may need to consider re-termination. Depending on joint type, a good jointer may be able to strip the existing joint without damaging the cable so you don't lose length.
RE: low IR of Power transformer
We've check the cable lugs but there are no sighn of any damage .
Does the cable of 1.6G ohm for 20kv is acceptable or not?
RE: low IR of Power transformer
20kV cables I have I tested and I got 2 Gohms!
AFAIK, insulation testing (Megger) is just one of the tests avaliable. The best way of knowing is for you to refer to the cable manufacturer/vendor. Please call them to be sure.
RE: low IR of Power transformer
RE: low IR of Power transformer
RE: low IR of Power transformer
they reason of replacing transformer is because of Differential protection trip and the insulation value was 200 kohm,
but now when we disconnect the defected transformer the disconnected cable insulation value was :
L1 24 G-ohm
L2 31 G-ohm
L3 1.6 G-ohm
before swapping the new transformer we are wondering about the statues of 20kv cable