New Weidmann study challenges the decades long belief regarding the thermal class of Transformerboard
A transformer’s capability of withstanding thermal, electrical and mechanical stresses is of primary consideration during long-term operation.
Image source: Weidmann
A transformer’s capability of withstanding thermal, electrical and mechanical stresses is of primary consideration during long-term operation.
Therefore, the thermal class standards of Transformerboard*, as part of the industry proven insulation system used in liquid-filled transformers, are a vital indicator of thermal performance and ultimately transformer lifetime diagnostics and monitoring. For decades, however, transformer pressboard has been widely rated simply to 105 °C. Some in the industry have even alluded to the necessity of ‘chemical treatments’ to slow down thermal aging at elevated temperatures, in order to apply it at a higher thermal class.
In a recent study, Weidmann Electrical Technology investigated the thermal aging performance of Transformerboard, as well as the sealed tube aging test procedure itself. In the 2011 edition of the IEEE C57.100 standard, a new sealed tube accelerated aging test procedure was introduced to determine the thermal class of solid and liquid insulation systems. The experimental work presented in the article investigated the effects of different test parameters on aging test results and data interpretation. The new findings on the dependence of the aging process on the ratio and type of materials in the system, as well as on the selected aging criteria, provide a better understanding of accelerated aging testing and the interpretation of aging data, along with practical recommendations for improvements to the test procedure.
In parallel, for the first time, the thermal index (and corresponding thermal class) of Weidmann Transformerboard, as a component of the ‘industry-proven ‘insulation system together with thermally upgraded kraft paper and mineral oil, was investigated and defined based on the standard industry test. The results confirmed that Transformerboard has a higher thermal class, which challenges the decades old assumption relating to the thermal class of Transformerboard as used in both power and distribution transformers.
*Tests were only conducted on Weidmann-manufactured Transformerboard, that adheres to our own internal specification and quality standard. No other manufacturers’ material was tested, nor can we comment on the performance of those materials.
Source: Weidmann
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