10 Nov 2025
Expert Oil Diganostic Services
Introduction
Transformer insulation systems, particularly those using cellulose-based paper, degrade over time due to thermal, chemical, and electrical stresses. Traditionally, ageing indicators such as carbon monoxide (CO), carbon dioxide (CO₂), and 2-furfural (2FAL) have been used to assess the condition of the insulation. However, these markers have limitations in sensitivity, stability, and reliability especially when the transformer is using thermal upgraded kraft paper (TUP).
TUP is commonly used in modern transformers due to its enhanced thermal stability and longer lifespan compared to traditional Kraft paper. However, traditional ageing markers like 2-furfural are less reliable for TUP because chemical stabilizers in the paper can suppress furfural formation.
Recent studies have identified methanol as promising early chemical marker for insulation ageing, escpecially in oil-paper insulation systems.
Why Methanol Works for TUP?
Methanol is released during the breakdown of celluloses' 1,4-β-glycosidic bonds, which occurs in both Kraft and thermally upgraded papers.
Unlike furfural(2FAL), methanol formation is not inhibited by the stabilizers used in TUP.
Methanol shows a consistent correlation with the degree of polymerization (DP), a key indicator of insulation health.
Correlation with ageing
Methanol concentration in oil increases steadily as the insulation ages, even in TUP.
Studies show methanol can be detected earlier than furfural, making it a more sensitive marker for early degradation.
Methanol levels can be used to estimate DP and predict insulation condition without needing to dismantle the transformer.
Advantages of Methanol for TUP Monitoring
Early detection of insulation degradation
Stable and reliable accros different paper types
Applicable to modern transformers using TUP
Supported by international standards (ASTM,IEC)
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For more info on our insulating oil analysis services, please do not hesitate to contact our team members:
Shaily Hatun Mohamad Saleh (shaily.saleh@tnb.com.my)
Muhammad Hadi Ahmad Fauzi (hadi.fauzi@tnb.com.my)
Roshaniza Ismail (roshaniza.ismail@tnb.com.my)
Nur Syahida Akryl Azam (nursyahida.azam@tnb.com.my)