Top Of The Class – The K-Class Transformer Fluid

KNAN, KNAF, ONAN, ONAF – what do they mean?  Here’s how to unlock the cooling class code for liquid filled transformers.

The ANSI/IEE Standard C57.12.00 defines a 4 character code to describe the cooling attributes of the transformer.  The first letter refers to the main cooling medium (i.e. in contact with the windings).  Decode as follows:

O = mineral or synthetic oil with a flash point less than 300 degrees
K = insulating fluid with a flash point greater than 300 degrees (K-class fluid)

The second letter designates the circulation mechanism for the main cooling medium.  It may be:

F = forced
N = natural
D = forced through a cooler

The third letter refers to the external cooling media, which can only be one of two options:

A = air
W = water

Leaving the fourth letter to designate how the external cooling media operates.  It can be:

F = forced (e.g. fans or pumps)
N = natural (convection)

Thus by way of example ‘KNAF’ designates a non-mineral oil filled unit (likely a synthetic ester) that has natural convection flow in the tank and utilizes fan cooling externally.

Of special interest to Benzoil is the first letter, O or K.  Benzoil supplies standard mineral oils (the O), plus we stock non-mineral oils (the K) such as silicone oil, synthetic esters and natural esters.  The flash point is the differentiator.

Note that some technical literature refers to fire point, and some to flash point.  There is a subtle difference, and the fire point is always higher that flash point.  For the avoidance of doubt, IEE Standard C57.12.00 makes reference to fire point.

By definition the flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air.  The fire point is the temperature at which the vapour continues to burn after being ignited.

There are environmental, health & safety and performance benefits of K-oils over O-oils, so ask Benzoil about changeouts, retrofills and transformer oil replacement programs today.  High flash point fluids we supply are suitable for use in transformers in hazardous locations where fire or explosion hazards exist.  This may be due to the presence of flammable gases and vapours, combustible dusts, or ignitable fibres present producing ignitable mixtures.  We stock the following:

Natural ester oils
Formulated from edible seed oils and bio-based feedstocks (canola, soybean), natural ester dielectric fluids are sustainable and renewable providing sustainable environmental protections.  Examples include:

  • Envirotemp FR3
  • Midel 1204
  • Midel 1215
  • NeuGen Plus

Synthetic ester oils
Synthetic esters are manufactured by combining alcohols and carboxylic acids in an esterification reaction.  The sophisticated chemistry allows the formulator to design oils to meet any insulating challenge.  Although not quite natural, synthetic esters do still exhibit the favourable health, toxicity and environmental benefits of more natural oils.  Examples include:

  • Envirotemp 200
  • Midel 7131
  • Dow Corning 561
  • Nycodiel

All the K-type oils have the required fire point (and flash point) over 300 degrees, so are suitable for any O to K oil replacement project.  Ask for our advice today.

By |2019-03-13T06:26:37+00:00February 8th, 2019|Architecture|