Ahmed Gamil

Natural ester (NE) dielectric liquids are increasingly specified for power transformers to improve fire safety, sustainability, and insulation-system reliability. This abstract compares FR3 (soybean-based) and FR3r (rapeseed/canola-based) NEs using the provided FR3r presentation and published technical information. FR3r was developed primarily for the European market to use a local crop and manufacture closer to OEMs, thereby shortening supply chains and reducing CO₂ footprint, while also addressing anticipated uncertainty around soy-related regulations and customer requests for a non soy NE alternative. Both fluids use an equivalent additive package and are presented as suitable and extensively proven for transformer application, with the key differentiation arising from base-oil fatty-acid composition, which shifts the balance among oxidation stability, low-temperature flow behavior, and gassing characteristics. In particular, the presentation highlights that oxidation stability is generally favored by stearic/oleic chains, whereas viscosity/pour point behavior is favored by polyunsaturated chains, and stray-gassing propensity is highly influenced by linolenic content. Consistent with this chemistry-driven trade space, FR3r is reported to exhibit lower pour point, higher viscosity at low temperatures, slightly higher oxidation stability after additive depletion, and higher gassing tendency relative to FR3. Thermal-property discussion further indicates that FR3 and FR3r have equivalent viscosity at typical operating temperatures, implying no expected impact on transformer temperature rise, while FR3r’s higher low-temperature viscosity may affect auxiliary components (e.g., flow indicators, pumps) during cold operation. From a standards and application perspective, FR3r is positioned to meet IEC 62770 and IEEE C57.147 and is marketed as a K class fluid derived from >99% rapeseed oil with no intentionally added petroleum, halogens, silicones, or sulphurs. FR3 is similarly specified as a bio-based NE dielectric coolant for distribution and power-class transformers, with widely cited acceptance limits including high flash/fire points (~330/360 °C) and a pour point of −10 °C in a representative data sheet. IEC guidance emphasizes that exposure of natural esters to air accelerates deterioration, so use is generally restricted to sealed units or conservators protected from the atmosphere (e.g., membranes). In this context, the FR3r presentation notes that under normal, non free breathing conditions, additive replenishment is not expected over transformer lifetime; when needed, inhibitor depletion can be tracked via oxidation induction time measured by PDSC (ASTM D6186) and replenished via premixed proprietary additives. Operationally, gassing behavior is a key practical differentiator. Literature reviews confirm that natural esters generally show positive gassing tendency compared with synthetic esters and that stray gassing can complicate fault interpretation if mineral-oil historical baselines are applied. Therefore, while FR3r’s higher gassing tendency may be manageable through updated diagnostics and trending, FR3r offers potential advantages in European sourcing and cold-flow specification, whereas FR3 benefits from extensive field history and widely published acceptance limits.

Keywords: FR3, FR3r, natural ester, rapeseed, soybean, oxidation stability, stray gassing