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Colour in Oil

transformer oil colour



IEEE Std C57.106-2006: Guide for Acceptance and Maintenance of Insulating Oil in Equipment provides the following recommendations;


1. Table 1 – Test Limits for Shipments of New Mineral Insulating Oil as Received from the Supplier: Color 0.5
2. Table 3 – Test Limits for New Mineral Insulating Oil Processed for Equipment, 230 kV Class and Above, Prior to Energization: 230kV - <345kV Color 1.0
3. Table 5 – Suggested Limits for Continued Use of Service-aged Insulating Oil: Color not specified.

IEC 60422:2005: International Standard Mineral Insulating Oils in Electrical – Supervision and Maintenance Guidance;


1. Table 3 – Recommended Limits for Mineral Insulating Oil After Filling in New Electrical Equipment Prior to Energization: >170kV Color 2.0
2. Table 5 – Application and Interpretation of Tests: Color and Appearance, Dark Colour is a symptom of chemical contamination or aging.




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 I, C and K 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.





TNB Transmission, SD T1, Malaysia. Although the oil to begin with was only colour 4, in order to bring the oil to colour 2, all other specifications were well above contract specifications and even new oil as shown in table1.


TNB Transmission, SD T1








A comparison can be made in table 2 with another transformer we reclaimed at M Power Station, M1 which started with an identical colour of 4 but was a different brand transformer filled with Shell Diala transformer oil;



TNB, SJM, 23/11kV 60MVA P Transformer BBT20



As can be seen, the colour to begin with was the same as SD T1 but the actual oil oxidation in the M transformer was much more advanced. Final oil condition was not as good as what we achieved at SD but the colour was lighter at 1.5.
Note: All testing recorded above was carried out by TNB research Sdn Bhd.




MH, I Client 13.8/230kV, 67.5/90/112.5 MVA K

Generator Transformer



N, A Client 180/240kV, 300 MVA ABB Transformers






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

esi transformer oil colour

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