Why is there a 25'C marking midway between Low and High on a liquid level gauge on transformers? Is the oil expanding and contracting with temperature and the needle showing the approximate tank level with respect to the oil temperature? Thanks for your input.
An oil level gauge is required so that the correct oil level can be maintained.
There is usually a mark on the gauge that indicates the 25°C level,
which is the proper oil level at that temperature. Maintaining the proper oil
level is extremely important because if the oil level falls below the level of
the radiator inlet, flow through the radiator will cease and the transformer
A very low oil level can expose energized and current-carrying components that are designed to operate in oil and could result in overheating or an electrical flashover. If the oil level is too high, it could cause over pressurization when the oil expands.
If the transformer is equipped with a constant-pressure nitrogen oil preservation system, then pressure gauges are included to measure the pressure of the gas blanket and the nitrogen in the make-up bottle.
John J Winders Jr Tx book