What does a furan test of transformer oil indicate about paper insulation?

Furan analysis measures chemical markers that are produced when cellulose paper insulation degrades. Higher furan concentration generally indicates advanced paper aging and reduced mechanical strength, which is critical for short circuit withstand capability. Furan results are interpreted with operating history, oil temperature, moisture, and oxygen exposure, because these factors affect aging rate. Furan testing is especially valuable for life assessment and asset management because paper condition cannot be measured directly without invasive inspection. Trending over time provides stronger insight than a single test result.