Page 47 - Energize March 2022

TECHNICAL

“A combination of online monitoring
and offline measurements is crucial in
identifying the condition of a transformer,”
states Wills. His colleague Sandy Woodley,
a sales manager for power products in
the UK and Ireland adds: “Implementing
more online testing can be a great starting
point in helping networks identify which
transformers might benefit from further
testing interventions. It can also help them
plan which transformers are likely to be
most fit to move into new positions on the
network if that is required.”

What tests should networks Figure 1: The bathtub curve: How asset age impacts transformer testing considerations (Power.com)
be carrying out on their
transformers?
There are myriad tests which might be bushing insulation and winding turn-to-turn insulation.
considered important for transformers, Asset owners need to consider which tests are likely to be most valuable to them for
depending on the types of stresses and any given asset and develop a maintenance regime which incorporates these, with specified
strains they tend to be subjected to. actions to take, if results within given ranges are returned. Actions might include oil
regeneration, degassing or drying.
Common tests
Common tests include winding ratio, What needs to change in transformer testing and why?
magnetisation current, insulation Efficiency and reliability are the main factors which should be driving networks towards
resistance and core ground tests, while increased transformer testing, Woodley says. “Network-wide changes instigated by
more advanced tests include frequency distributed generation and increased energy flexibility for example, have put an increased
response analysis, polarisation/ amount of pressure on the network – most of which is already running at capacity”, he adds.
depolarisation and recovery voltage Furthermore, with many transformers now classed as ageing assets, their ability to cope with
method. Some tests simply gauge the the additional strains created by more dynamic and variable power flows is limited, adds
operation of the transformer while others Wills. “The industry needs to know the condition of these assets so that any failures, and
will diagnose potential issues with its thus wider network issues, can be prevented,” Woodley states. On top of this, eliminating
condition, or any physical changes such unnecessary capital expenditure amid the post-pandemic financial squeeze is imperative for
as whether the insulation is deteriorating, utility firms, says Wills. “Making full use of transformer testing technology is one of the most
for example. Other problems detected by effective ways of ensuring asset interventions are made as and when they are needed, and
testing include magnetic circuit integrity that money and human effort are not expended unnecessarily.”
and insulation, winding geometry, It’s not just efficiency that lies in the balance, however. As exponential growth in the
winding/busing/OLTC continuity, winding/ connection of distributed low carbon technologies push more and more transformers to

Figure 2: The bathtub curve explained

energize | March 2022 | 45