ASTM D3487-25 PDF

Full title and description

Standard Specification for Mineral Insulating Liquid Used in Electrical Apparatus — ASTM D3487-25. This specification defines requirements for unused mineral insulating oils of petroleum origin intended for use as insulating and cooling media in power and distribution electrical apparatus (transformers, regulators, reactors, circuit breakers, switchgear and attendant equipment). It addresses two types of mineral insulating oil (Type I and Type II) and specifies physical, electrical and chemical property limits to ensure functional interchangeability and compatibility with existing apparatus and maintenance practices.

Abstract

ASTM D3487-25 establishes minimum property and performance requirements for new mineral insulating oils used in electrical equipment. The standard categorizes oils into Type I (normal oxidation resistance) and Type II (enhanced oxidation resistance) and lists required tests and limits for properties such as dielectric breakdown strength, dissipation factor, interfacial tension, oxidation stability, inhibitor content, corrosive sulfur, water content, neutralization number (acid number), PCB content, viscosity, pour point, flash point, color and visual appearance. The aim is to ensure oils are miscible and compatible with existing insulating liquids and apparatus and will maintain functional characteristics in service.

General information

• Status: Active
• Publication date: May 16, 2025
• Publisher: ASTM International
• ICS / categories: 29.040.10 (Insulating oils for electrical apparatus); Committee D27 (Electrical Insulating Liquids and Gases)
• Edition / version: ASTM D3487-25
• Number of pages: 6

Scope

This specification applies to unused mineral insulating oil of petroleum origin as received (prior to any processing) for use as an insulating and cooling medium in new and existing power and distribution electrical apparatus (for example, transformers, regulators, reactors, circuit breakers, switchgear and related equipment). It is intended to define oils that are functionally interchangeable and miscible with existing oils and compatible with equipment and standard field maintenance. The standard covers required physical, electrical and chemical property limits and references associated test methods.

Key topics and requirements

• Classification into Type I (normal oxidation resistance) and Type II (enhanced oxidation resistance).
• Electrical requirements including minimum dielectric breakdown voltage and limits on dissipation factor (power factor).
• Physical property limits such as viscosity (at specified temperatures), pour point, flash point, color and visual appearance.
• Chemical requirements: oxidation stability, inhibitor content, neutralization (acid) number, water content and limits on corrosive sulfur and PCB contamination.
• Interfacial tension and miscibility criteria to assure compatibility with other insulating liquids.
• Referenced test methods for verification (ASTM electrical, physical and chemical test methods).
• Requirement that values are stated in SI units (with customary units for information where applicable).

Typical use and users

Primary users are electric utilities, transformer and switchgear manufacturers, electrical equipment design and maintenance engineers, testing and certification laboratories, procurement/specification teams, and consultants focused on asset management and dielectric fluid selection. Typical uses include specification and acceptance of new transformer and switchgear oils, procurement documents, product qualification testing, and compatibility assessments during equipment refurbishment or retrofilling.

Related standards

Commonly referenced and related documents include ASTM test methods and specifications used to verify properties called out in D3487 (for example, ASTM D1816 for dielectric breakdown, ASTM D924 for dissipation factor/power factor, ASTM D971 for interfacial tension, ASTM D2440 for oxidation stability, ASTM D4059 for PCB analysis, ASTM D1500/D1524 for color/appearance, ASTM D97 for pour point, ASTM D92 for flash point, ASTM D445 for kinematic viscosity). Related industry standards and guides include IEEE guides on insulating oil handling and acceptance (for example IEEE guide for maintenance and acceptance procedures) and international standards on mineral insulating oils (for example, IEC specifications for insulating oils).

Keywords

mineral insulating oil, transformer oil, insulating liquid, dielectric strength, oxidation stability, Type I, Type II, dielectric breakdown, dissipation factor, interfacial tension, corrosive sulfur, PCB limits, oil specification

FAQ

Q: What is this standard?

A: ASTM D3487-25 is the ASTM International standard specification that defines property and acceptance limits for unused mineral insulating oils intended for use in electrical apparatus such as transformers and switchgear.

Q: What does it cover?

A: It covers two types of new mineral insulating oils (Type I and Type II) and specifies electrical, physical and chemical property requirements and referenced test methods to ensure oils are compatible, miscible and functionally suitable for power and distribution electrical equipment.

Q: Who typically uses it?

A: Electric utilities, equipment manufacturers, maintenance engineers, testing laboratories, procurement/spec writers and consultants involved in specifying, testing, purchasing or maintaining insulating oils for electrical equipment.

Q: Is it current or superseded?

A: As published it is the current active edition (ASTM D3487-25). Users should confirm the edition in force at the time of procurement or testing because standards may be revised.

Q: Is it part of a series?

A: It is part of ASTM Committee D27 work on electrical insulating liquids and references numerous ASTM test methods and related documents. It is commonly used alongside other ASTM methods and IEEE/IEC guidance for insulating oils and equipment maintenance.

Q: What are the key keywords?

A: Mineral insulating oil, transformer oil, insulating liquid, dielectric breakdown, oxidation stability, Type I, Type II, interfacial tension, corrosive sulfur, PCB.