H2scan TM Catalog 2025 - Flipbook - Page 28
2. Factors in determining life expectancy
When trying to understand how long a transformer will last,
we can think of it like buying a used car. A car’s life expectancy
is going to depend on how it is driven, where it is driven, the
maintenance history, and so on. It will also depend on its
current operating conditions. Has the recommended
maintenance been performed? Has the car been in any
accidents, and so on. There’s a lot to consider. Likewise, not
surprisingly, the questions for power transformers are a little
different, but the general approach is the same. In order to
understand how long a transformer will last, you need to look
at a number of important factors, including the manufacturer,
the age, and how hard its life has been.
As the current lead time for new power transformers ranges
from 1 to 3+ years, how are asset managers coping with
their aged transformer 昀氀eets? Age, by itself, is not necessarily
an indicator of deterioration—but the longer a unit has been
exposed to high temperatures and repeated through faults,
the less likely it will survive future system disturbances.
These real-world operational ‘bumps in the road’ reduce the
mechanical strength of the solid insulation, exposing the
unit to an increased chance of failure from future faults or
contingency loading.
One of the key things every asset manager wants to know is
how long to expect their transformers to last. Replacing
transformers takes considerable effort from many parts of
a utility, including Operations, Engineering, and, don’t forget,
Finance. Money needs to be available to cover those costs.
In addition to money, managers face long wait times for new
transformer orders. Of course, it is not as easy as looking into
a crystal ball to estimate when a transformer will fail. Many
factors must be considered. The transformer speci昀椀cation,
design, manufacturer, factory test performance, maintenance
history and operational history all affect transformer life.
One way to estimate the life of transformers is to look at
publicly available data. Rough guidance can be obtained from
looking at the data that was used to derive dissolved gas
standards in transformer insulating liquid for the 2019 Std
IEEE C57.104 – IEEE Guide for the Interpretation of Gases
Generated in Mineral Oil-Immersed Transformers [2]. The data
set used to derive the standard contained nearly 1.4 million
oil samples from over 300,000 transformers. Many labs and
utilities provided data to support this effort. The data shows
very few oil samples were analyzed for transformers aged 60
years and older.
Similar data published in the 2015 CIGRE Transformer
Reliability Survey [3] shows the age pro昀椀le of over 7000
transformers from a North American data set of in-service
transformers. While the rise and fall of the data from year to
year indicates, to some extent, periods of grid expansion, it is
signi昀椀cant that the trend from 45 to 60 years indicates that
after 45 years, it’s much more likely transformers will be
removed from service, and there is virtually no expectation
a transformer will last past 65 years old.
Figure 1. In North America, a low number of large power transformers were added to the grid in the 90s, causing manufacturing to
shift to Asia [4]
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