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Charred Paper Fiber From Transformer Oil Under the Microscope

Charred Paper Fiber From Transformer Oil

This charred paper particle is from an oil sample collected from a 8400kVA transformer. This transformer was reportedly gas blanketed and sealed. This particle shows the contours of the paper fibers and the edge fracture pattern typical of charred paper. These patterns are often absent in charred paper, in which case the origin of the char can not be determined directly. When these patterns are present the origin of the char can be determined. These particles indicate heating of the paper insulation in excess of 250 degrees Celsius.

Transmitted Oblique Off Crossed Circular Polarized Light and Darfield Reflected light Illumination


Charred paper fiber is paper fiber that has been heated to a high enough temperature for a long enough time to loose much of its hydrogen and hydroxyl groups and to increase the carbon coordination in its structure. I this process the fiber becomes increasingly opaque, it shrinks, and the reflectivity of the surface of the fiber increases. The structure of the fiber is often maintained during this process.

Significance in the Environment:

Charred paper fiber in transformer oil often indicates a significant hotspot in the core at some location.

Characteristic Features:

Associated Particles:

Charred paper fiber is generally associated with much greater numbers of severely degraded paper fiber. The severely degraded paper fiber is created at an earlier stage in the formation of a hotspot.