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KNAN and ONAN Transformers Explained: Key Differences, Oil Types and Transformer Cooling.

IEC cooling class codes for power transformers and distribution transformers define safety performance, environmental impact, maintenance requirements, and asset lifespan. It's a key component in the design and specification of all transformers.

Why Transformer Oil Is Critical in Power & Distribution Transformers

Transformer oil plays a vital role in both power transformer performance and distribution transformer reliability. Four Key Functions of Transformer Oil are:

  • Dielectric insulation – Provides electrical insulation between components
  • Cooling medium – Transfers heat away from windings
  • Protection of insulation – Prevents moisture and oxygen damage to paper insulation
  • Diagnostics tool – Enables condition monitoring through oil testing (e.g., DGA)

Choosing the right insulating fluid is essential in mining, where harsh conditions and remote locations demand reliability

Let's understand more about the differences between KNAN and ONAN oils for Mining Projects

Features ONAN (Mineral Oil) KNAN (Natural Ester)
Flash Point ~160°C ~360°C
Fire Behaviour Sustains combustion Self-extinguishing
Environmental Impact Hazardous, non-biodegradable Biodegradable, non-toxic
Moisture Tolerance ~60 ppm ~800–1050 ppm
Cost Lower Higher upfront
Transformer Design Standard Requires sealed system
Insurance Impact Standard Potentially reduced premiums

Why This Matters for EPCM, EPC's and Mine Owners. 

Fire Risk and Safety

  • In underground and high-density installations, KNAN transformers significantly reduce fire risk, improving personnel safety and compliance.

Environmental Protection

  • Spills of mineral oil can contaminate groundwater at very low concentrations. Ester fluids provide a non-toxic, biodegradable alternative, critical in both African and Australian regulatory environments.

Asset Life and Reliability

  • Higher moisture tolerance in ester fluids helps preserve paper insulation, potentially extending transformer life under the same loading conditions.

Total Cost of Ownership

  • While KNAN solutions have higher upfront costs, they can reduce:fire mitigation infrastructure, environmental remediation risk, Insurance costs and long-term replacement frequency

Transformer Oil Interchangeability FAQ's

Training

In general, older mineral insulating oils are compatible and can be mixed with one another. However, this does not apply to newer insulating fluids, particularly ester-based oils.

No. Most newer oils—especially natural ester fluids—are not suitable for mixing with traditional mineral oils. Mixing these fluids can negatively impact performance and safety.

Mixing incompatible transformer oils can lead to:

  • Reduced flash point, increasing fire risk
  • Degraded dielectric strength
  • Compromised cooling performance
  • Potential long-term transformer damage

Even small levels of contamination can alter the oil’s characteristics.

In some cases, a small amount of contamination may be tolerated, but:

  • A maximum of ~7% mineral oil in ester fluid is typically allowed
  • Beyond this level, key properties—especially fire safety performance—are significantly reduced

It is not recommended. While trace contamination may occur during maintenance, deliberate mixing should be avoided due to:

  • Reduced fire resistance
  • Lower flash point (potentially below 300°C)
  • Loss of environmental benefits

Ready to optimise your transformer specification for safety, reliability and compliance?

At PTI, we work hand-in-hand with key project stakeholders to ensure transformer solutions are not only compliant but technically robust, fully documented and defensible under engineering review.

Our team supports projects with:

  • Detailed compliance verification to IEC and ANSI/IEEE standards
  • ISO/IEC 17025-aligned testing transparency
  • Complete QA/QC documentation packs
  • FAT coordination and witnessing support
  • Technical clarification during tender and bid evaluation
  • Engineering assurance throughout the project lifecycle

We understand that in EPCM and owner-led projects, technical governance and documentation integrity are just as important as performance.

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