IEC 60076-7:2005 - Loss of Life of Transformers
IEC 60076-7:2005 - Loss of Life of Transformers
(OP)
Hi all,
The IEC 60076-7 provides a mathematical approach of finding the loss of life of transformer. I have recently been involved in finding how much to overload a transformer without causing significant Loss of Life.
I just want to make sure that my understanding of the IEC standard is correct.
Table 4 gives you the limits of Normal cyclic loading, Long time emergency loading and short time emergency loading. My understanding is that these limits values, if ever exceeded, will cause permanent damage to the transformer. However, it implies that the loss of life will be 'accelerated' compared to normal loss of life for a transformer operated at rated loading.
I do understand that if factors such as low ambient temperatures or forced cooling are used after the overload condition, this will produce a normal loss of life.
Finally, anyone with a fair guess the life of a transformer if properly maintain. We have transformers more than 60 years and perfectly fine.
Thank you
kevin
The IEC 60076-7 provides a mathematical approach of finding the loss of life of transformer. I have recently been involved in finding how much to overload a transformer without causing significant Loss of Life.
I just want to make sure that my understanding of the IEC standard is correct.
Table 4 gives you the limits of Normal cyclic loading, Long time emergency loading and short time emergency loading. My understanding is that these limits values, if ever exceeded, will cause permanent damage to the transformer. However, it implies that the loss of life will be 'accelerated' compared to normal loss of life for a transformer operated at rated loading.
I do understand that if factors such as low ambient temperatures or forced cooling are used after the overload condition, this will produce a normal loss of life.
Finally, anyone with a fair guess the life of a transformer if properly maintain. We have transformers more than 60 years and perfectly fine.
Thank you
kevin






RE: IEC 60076-7:2005 - Loss of Life of Transformers
The following should be considered when reading the Loading Guide:
1) The loading guide assumes that the transformer's life is determined by failure modes based on chemical reactions. This is true for many of the important failure modes, e.g. paper degrading, but not true for some other failure modes.
2) The temperature dependence of reaction rates for chemical reactions is explained by the Arrheniu's equation. The equation gives reaction rates based on absolute temperature, therefore the loading guide uses the absolute temperature of the transformer (and not the temperature rise above ambient).
3) There is no such thing as a normal life expectancy for a transformer, it "depends".
4) How good are the transformers that have been operating perfectly fine for 60 years? Can they withstand a short-circuit without a tank rupture? Determining the "end of life" can be tricky.
Best regards,
Jens
RE: IEC 60076-7:2005 - Loss of Life of Transformers
Thank you for your reply. Again I lay emphasis on Table 4 of the IEC in relation to the loss of life. Am I right in my understanding of it?
Thank you
Regards
kevin
RE: IEC 60076-7:2005 - Loss of Life of Transformers
It also depends on overhead in the transformer design. I've seen 65° C rise transformers range anywhere from 45° C to 66-68° C rise (penalty applies) at rated MVA during heat run tests.
RE: IEC 60076-7:2005 - Loss of Life of Transformers
Perhaps the longevity of power transformer could be attributed to advance in insulation materials, overvoltage protection with metal oxide surge arrester, protective relays, better manufacturing QA/QC process, etc. Design safety margin on the other hand, has been reduced in the pass decades do to competitions and advance computer tools.
According with a FERC report, the average age of installed large power transformer (>100 MVA) in the United States is approximately 38 to 40 years, with 70 percent of being 25 years or older. While the life expectancy of a power transformer varies depending on how it is used, aging power transformers are potentially subject to an increased risk of failure.
Fundamentally, the major components of a transformer are windings with associated solid insulation, and the steel parts e.g. core, frame, and tank. The steel parts can last for many years. This is true also for the copper, from which the windings are made. This is however not the case with the insulation system.
IEC 354 thermal model for transformer hottest-spot calculations is very similar to the IEEE Std. C57.91-1995 classical model. Should be noted that
transformer failure could be best characterized as a stochastic (probabilistic) model rather than a deterministic approach. For illustration, below are a few graphics and picture from various source showing basic probabilistic tools to consider in failures analysis in power transformer. Hope this help with the discussion.
RE: IEC 60076-7:2005 - Loss of Life of Transformers
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RE: IEC 60076-7:2005 - Loss of Life of Transformers
Regarding table 4:
I share your understanding of the guide; exceeding the limits in table 4 can lead to permanent damage but when operating within the limits of table 4 the relative aging calculations apply.
Rgs.
Jens
RE: IEC 60076-7:2005 - Loss of Life of Transformers
RE: IEC 60076-7:2005 - Loss of Life of Transformers
Highly Appreciated
Cheers
Kevin