Bubble Formation from Non-Thermally Upgraded Kraft Paper in Alternative Insulating Liquids

Bubble formation in transformers could lead to their failure, resulting in severe outages in the electricity network. Hence, understanding the parameters that impact the bubble formation process is crucial to maintain the transformer's dependable operation. Commonly, mineral oil and non-thermally upgraded Kraft paper have been used as the insulating materials for power transformers, and the risk of bubble formation has been studied for this material combination. However, new insulating liquids such as esters and gas-to-liquid technology-based oils are recently gaining more popularity and studies on bubble formation for these alternative liquids are limited. In this paper, the impact of alternative liquids on bubble formation has been investigated by using a small-scale test tube-based system. Studies have shown that when considering the water content in the paper at the time of bubble formation, the bubble formation temperature is comparable across different liquid types.</p

Development of an Experimental Setup to Study the Bubble Formation of Transformer Insulation Systems

Bubbles in transformers caused by overloading could weaken the insulation system and lead to dielectric failures. The bubble formation process has been studied for many decades and results have led to the hot-spot temperature constraint of 140 °C for 2% of water content in cellulose. This paper utilizes a small-scale test system to observe the randomness in the bubble formation process and hence to study the suitability of such a single temperature-water content in paper relationship to describe bubble formation. Multiple tests conducted with the same initial water content in paper have shown that bubble inception time and temperature can vary under same initial conditions.</p

Evaluation of Bubble Formation in Transformer Insulation Systems - a Step Forward

Bubble formation in transformers could result in severe consequences leading to power outages and huge financial losses. There is an increased risk of bubble formation in the future due to increasing load demand and much higher loading fluctuations. The bubble formation process in transformer insulation has been studied for decades and the water content in the paper has been addressed as the most influential impact parameter. However, results from the most common insulating material combination of Kraft paper and mineral oil vary widely and a meaningful comparison for other parameters or insulating material combinations is challenging. This paper presents the development and verification of a simple test setup that can be used to study various impact factors on the bubble formation process with a high degree of confidence.</p