Compatibility evaluation of nitrile rubber formulations with insulating fluids (IMO and INE) used in power transformer

ABSTRACT

Power transformers are essential equipment in the electric energy generation and distribution processes and are usually chosen with paper and insulating fluids. Insulating fluids have a dual function of insulation and heat exchange. Proper sealing of this equipment is essential to prevent leaks of the insulating fluid, which can cause a reduction in the life of the transformer, as well as environmental problems. Different compositions were formulated in nitrile rubber (NBR) compatible with those used as seals in power transformers, with different acrylonitrile contents (35 and 44%) and dicumyl peroxide (6.0 / 8.0 and 10.0 phr). The aging tests were conducted systematically under three conditions: insulating mineral oil (IMO), insulating natural ester (INE) soy and corn, traditionally used as insulating fluid in power transformers. The effects of the thermal aging of nitrile rubber on IMO and ENI, as well as the effects of the cross-linking content of the chains were studied using characterization methods such as oscillating disk rheometry, swelling, variation in mass, volume and Shore A hardness. The density of crosslinks and the average molar mass between the links were also determined by the Flory-Rehner theory. Changes in physical properties during the aging process were analyzed and compared. It was possible to observe a different behavior in the sealing elastomers when aged in IMO and ENI influenced by the crosslinks and acrylonitrile contents in the samples.

Keywords
Power transformers; Insulating mineral oil; Insulating natural ester; Nitrile rubber; Compatibility