Transformer Oil Level Check
Transformer Oil Level Check
(OP)
EE's,
I have a question about checking oil level in transformers. We recently checked the oil level in all of our transformers. We connected a fitting to the drain valve and then connected tygon tubing and held the tubing to the height of the transformer. We cracked the drain valve open and visually could see if the oil level was just above the radiator fins. The end of the tygon tubing was to atmosphere. That method worked on a few transformers. When performing this method on GE Prolec transformers we had to connect the end of the tygon tube to a port on a pressure gauge (negative/positive psig) located at the top of the transformer to see the correct oil level. When the end of the tubing was to atmosphere the oil level in the tygon tubing would be well below the radiator fins like 16-in. or more. Can someone tell me why we had to perform the oil level test differently?
I have a question about checking oil level in transformers. We recently checked the oil level in all of our transformers. We connected a fitting to the drain valve and then connected tygon tubing and held the tubing to the height of the transformer. We cracked the drain valve open and visually could see if the oil level was just above the radiator fins. The end of the tygon tubing was to atmosphere. That method worked on a few transformers. When performing this method on GE Prolec transformers we had to connect the end of the tygon tube to a port on a pressure gauge (negative/positive psig) located at the top of the transformer to see the correct oil level. When the end of the tubing was to atmosphere the oil level in the tygon tubing would be well below the radiator fins like 16-in. or more. Can someone tell me why we had to perform the oil level test differently?





RE: Transformer Oil Level Check
It is common for the tank pressure in many transformers to be either above or below atmospheric pressure depending on the oil temperature and the ambient atmospheric pressure. With one end of the tubing open to the atmosphere you are measuring a combination of the oil level and the internal pressure. The internal pressure may change from positive to negative as the oil temperature changes.
Bill
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"Why not the best?"
Jimmy Carter
RE: Transformer Oil Level Check
RE: Transformer Oil Level Check
RE: Transformer Oil Level Check
No liquid at your probing height yields no backwall pulse reflection.
-AK2DM
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"It's the questions that drive us"
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RE: Transformer Oil Level Check
Record the ambient and tank temperature
RE: Transformer Oil Level Check
RE: Transformer Oil Level Check
The pressure due to fluid at penetration elevation must be same inside and outside the tank.
(Rho*g*h)inside + Papplied_inside = (Rho*g*h)outside + Papplied_outside
Where rho is density (depends on temperature as mentioned), g is acceleration of gravity, h is height, Papplied is pressure of gas above the fluid.
You can see that density difference or difference in pressure applied will cause the height outside to differ from height inside.
Also if there is flow in the neighborhood of the tap there may be dynamic effects not captured in above equation.
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(2B)+(2B)' ?
RE: Transformer Oil Level Check
RE: Transformer Oil Level Check
The nameplate should have on it what the correct oil level is. Another way, if you don't trust the level gauges, is to use an infrared camera. There should be a difference of temperature between the oil and air space.