Free module. This page is free to read. It does not ask you to sign in. It does not offer a class or a call. Use the edition of each standard named in the contract. Questions: hello@transformerpath.com.
Volume 7 is dielectrics, cellulose, oil, and the clocks they keep. This module is the system view. It does not size a duct, pick a paper thickness, or quote a withstand stress. Those are design steps on the paid plan, and they depend on the edition named in the contract. What this page fixes is that the oil and the paper are not two separate products that happen to share a tank.
The oil does three jobs
In a liquid-immersed unit the oil insulates, it carries heat, and it is the sample you can take without opening the tank. Mineral oil is specified by the oil standard the contract names. Esters and other liquids are specified by their own standards, usually because of fire behaviour or environmental duty, and they are not a drop-in correction to a mineral-oil temperature-rise design. The cooling code and the thermal class have to be read with the liquid that is actually in the tank. A nameplate that says only “oil” has not identified which liquid the limits were written for.
Cellulose — the paper on the conductor and the pressboard that forms barriers and cylinders — holds most of the water in the unit. Water moves between paper and oil as temperature changes. A single oil moisture reading, without the temperature and the load at sampling, does not say how wet the paper is. Heat is the other clock: paper ages faster as it runs hotter. Oxygen, where a free-breathing conservator admits it, is a third. Sealing arrangements exist to keep one or more of those clocks slow. They do not stop the clocks.
Barriers divide a weak gap
A long oil gap is weaker, for its length, than the same distance broken into short gaps by solid barriers. That is the point of the pressboard structure around a winding. Creepage along a surface is a different and usually weaker path than a puncture through the solid. Angle rings and caps exist to make that surface path longer and to turn it across the stress. This module does not give a stress in kilovolts per millimetre. Any such number has to come from the design rules and the test levels in the contract, not from a rule of thumb carried between projects.
- Name the liquid. Mineral oil, ester, and silicone are different specifications and different thermal designs.
- Most of the water sits in the cellulose. An oil sample needs its temperature.
- Temperature, moisture, and oxygen are the aging clocks. Sealing slows a clock. It does not delete it.
- Barriers subdivide oil gaps. A single large gap is not the same insulation as several small ones.
Grading, impulse distribution, and drying practice stay on the paid plan. This page does not set a clearance.
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