IEC 62770:2024

Overview

IEC 62770:2024 - “Fluids for electrotechnical applications – Unused natural esters for transformers and similar electrical equipment” - is the 2nd edition international standard that specifies properties, test methods and delivery requirements for unused natural esters used as insulating and heat‑transfer fluids in transformers and similar liquid‑immersed electrical equipment. The standard covers performance, electrical, physical, chemical and health/safety/environmental (HSE) characteristics of new (unused) vegetable‑oil based triglyceride fluids and clarifies that natural esters are intended for use in sealed transformers or equipment where the conservator tank is protected from atmospheric contact (e.g., membrane systems) because exposure to air accelerates oxidation and deterioration.

Key topics and technical requirements

• Scope and classification: Definitions for natural esters and classification of fluid types for electrotechnical use.
• Physical properties: Tests and acceptance attributes for appearance/colour, viscosity, pour point (including LCSET cold‑temperature considerations), water content and density.
• Electrical properties: Requirements and test procedures for breakdown voltage, dielectric dissipation factor (DDF) and relative permittivity.
• Chemical properties: Determination of acidity, corrosive sulfur, additive declaration and furfural content.
• Performance & stability: Oxidation stability test methods (normative Annex A) and guidance on additive use and declaration.
• HSE considerations: Fire and flash points (measured by Cleveland Open Cup), PCB exclusion, biodegradability and emphasis on aquatic toxicity.
• Sampling, identification and delivery: Procedures for sampling, labelling and general delivery requirements for unused natural esters.
• Test method updates: The standard adopts Cleveland Open Cup for flash/fire point (Pensky‑Martens closed cup deemed problematic for natural esters) and references IEC 63012 for other liquid types.

Practical applications and users

IEC 62770 is used by:

• Transformer and reactor manufacturers selecting and specifying insulating fluids.
• Utilities and asset owners assessing retrofit or new‑build use of natural esters for improved fire safety and environmental profile.
• Test laboratories performing dielectric, chemical and oxidation stability testing.
• Procurement teams writing technical specifications and certificates of conformity.
• Safety, environmental and regulatory teams evaluating biodegradability, aquatic toxicity and disposal requirements.

Natural esters are chosen where higher fire points and improved environmental compatibility are priorities, but only when equipment design prevents air ingress.

Related standards

• IEC 63012 - for other insulating liquids and low‑viscosity esters; referenced in IEC 62770 as complementary guidance.

Keywords: IEC 62770, natural esters, transformer fluids, insulating fluids, oxidation stability, dielectric properties, Cleveland Open Cup, biodegradability, sealed transformers.