Transformer Oil Level Guage

[mpeck1982]

Hello EE,

How do you know how much oil you have in your transformer with a level gauge that has the indication of Low, 25 deg C, and Hi? The needle of the level guage is currently slightly higher than 25 deg C. Am I suppose to reference that temperature to the transformer oil temperature guage? Any ideas?

 

[crshears]

Maybe I should have made my handle "former operator"...

In my utility the transformer oil level gauge is typically mounted on what we call the "conservator," which is in truth a head tank that allows for the expansion and contraction of the transformer's oil with loading and ambient temperature changes.

You are intuiting correctly: conservators are typically sized to a specified minimum ratio of transformer tank volume such that neither will the conservator overflow when the oil reaches its hottest temperature nor the transformer tank inhale [for lack of a better term] air when the oil reaches its coldest temperature. The oil level gauge is so positioned and its float adjustment so calibrated that, when the transformer oil in both the transformer tank and conservator is at 25°C, the needle on the transformer oil gauge should point very closely if not precisely to the 25°C index mark on the gauge.

As part of a transformer inspection, operators / field staff routinely cross check the position of the pointer against the prevailing oil temperature as a means of determining whether the transformer in question contains the proper amount of oil.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[ScottyUK]

These are common on the tank walls of smaller transformers. They typically show the nominal level at (around here) 15°C with a line etched on the glass and have a 'high' and 'low' level. I wouldn't worry unless it is very high or very low - if you can see the surface of the oil in the sight glass then it is ok. The markings are fairly rudimentary in my experience - I certainly wouldn't class it as being an instrument for measurement purposes.

 

[prc]

Today most of the Power transformers are provided with an air cell (Diaphragm)membrane inside conservator to prevent direct contact of oil with atmosphere.In such cases there will be two oil level gauges-one magnetic oil level gauge actuated by the position of membrane,indicating actual oil level inside and other an oil sight window which shall be full always and level will come down only when the membrane breaks or a break somewhere through which breathing occurs.

With such arrangement, it is important to fill or keep oil level exactly corresponding to the oil temperature. In case more oil is filled, it will result in excess pressure inside transformer when loaded.This will lead to weld cracks in tank welding or/ cum operation of pressure relief device, spilling out oil.