Regenerated Transformer Oil Colour Standards

Source of Colour Used In Oil

Chemical contamination is typically colour absorbed from the type of varnish used on the windings or resins used in the cellulose pressboard packers and spacers. It can also be a result of using too high temperature or inadequate vacuum during oil filling or subsequent treatment causing damage to the oil cellular structure. Rusting inside the transformer will also cause colour contamination. Colour introduced by these mechanisms cannot be removed by Fullers Earth Treatment.

Aging is from the normal oxidation process and most of the colour introduced by oxidation can be removed through Fullers Earth. Particulate Contamination can be drawn in from the atmosphere via silica gel breathers, carbon from switching or arcing faults, residual contamination from manufacture and assembly. Colour from particulate contamination can generally be removed quite quickly by Fullers Earth and even Purification.


Over more than 25 years of experience in Oil Reclamation we find that Transformers and Oil from India, China and Korea tend to have very much darker in-service oil compared to the same oil condition of other sources. We believe this is a result of the materials used in construction as well as the base stock from which the transformer oil is refined.


1. TNB Transmission, Malaysia: Contract Acceptance Specification for On-line Reclamation of 132 kV, 230 kV and 400kV Transformers – Color max 2.5

2. PLN Transmission, Indonesia: Contract Acceptance Specification for On-line Reclamation of 150 kV and 500kV Transformers – Color max 3.0

3. NGCP, Philippines: Contract Acceptance Specification for On-line Reclamation of 240kV Tranformers – Color max 2.0

4. Transpower, New Zealand: Contract Acceptance for Online Reclamation of 230kV Transformers – Not Specified

5. TransGrid, SPI Power Net, ETSA, Powerlink, Australia: Contract Accetance for On-line Reclamation of HV Transmission Transformers – Not Specified