Page 61 - Energize June 2022

TECHNICAL

TABLE 3: PARTICLES - Table B.1 - Typical contamination levels (particles) encountered in power transformer insulating oil as measured using IEC 60970 5

Flashpoint temperature: Not a routine test. If there is a maximum makes it possible to see the supposed reliability of a specific unit
decrease in flashpoints by 10%, the equipment might require at a specific date and time. This makes it possible to ensure best
further inspection. This value might differ in different countries. It practice application and optimised maintenance. It also makes it
is advisable to perform this test when an unusual odour is noticed, easier to draw up a maintenance plan and action plan.
the unit has been refilled, or an internal fault has occurred.
References
PCB (polychlorinated biphenyls): This test is not to determine the 1. IEC 60422 Edition 4.0, 2013/01 International Standard (Mineral
condition of the transformer; this is a health and safety impact test. insulating oils in electrical equipment – supervision and
PCB is hazardous to both humans and the environment; it is vital to maintenance guide).
test for PCBs after the retro fill of a transformer. It is also required 2. A Shkolnik: “Oxidation inhibitor and reinhabiting oil-filled
whenever any maintenance has been done on the unit, and the transformers”.
possibility of contamination is present. If PCB content exceeds the 3. L Lewand: “Passivators, what they are and how they work”,
recommended limits, the appropriate action needs to be taken. Doble Engineering Company.
Units with a PCB content of more than 50 ppm require a fire safety 4. CIGRE technical brochure 378, 2009: “Copper sulfide in
plan, environmental protection plan, and extra precautionary Transformer Insulation”
measures when maintenance is done. This oil needs to be replaced, 5. CIGRE Technical Brochure 157, 2000: “Effect of particles on
and the oil disposed of as hazardous waste, with a certificate of transformer dielectric strength”
safe disposal issued to the equipment owner. Local regulatory 6. Article initially published by Transformer Technology Magazine
bodies define the limits. Issue 16 – December 2021, https://www.transformer-
technology.com
DGA (dissolved gas analysis): Since DGA is an intricate science with
a lot of data and interpretation, we will discuss this phenomenon About the author
in another article. The limits for the different gases and the Corné Dames is a WearCheck transformer consultant. She has
interpretation of this data according to international standards over 20 years’ experience in the industry, having previously
will be discussed in detail, forming part of the overall health rating worked as laboratory manager for a major industrial laboratory
determination of the transformer. group, focusing on transformer health. She has been intrigued
by transformer chemistry right from the start of her career,
Conclusion particularly in the analysis of test data. Dames has vast practical
Transformer condition monitoring is an interlaced, highly exciting and theoretical knowledge of reliability maintenance programmes.
field of study. In this article, we focused on the types of tests to
determine the condition of the transformer, the critical values, Contact WearCheck, Phone 031 700-5460,
and the recommended actions. The Health Index indication support@wearcheck.co.za, www.wearcheck.co.za

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