Page 46 - Energize March 2022

TECHNICAL

Why it’s time to revisit

transformer testing regimes

Today’s energy networks face looming challenges from a relentless and accelerating process of
decarbonisation and decentralisation across the energy system.

INFORMATION FROM MEGGER

hese forces, which equate to However, as pressure and reliance on the performance of transformers on the
proliferating connections of distribution network increases, Megger’s experts argue it is time for a rethink on the depth
Tdistributed low carbon technologies, and breadth of testing conducted. In particular, they argue for a review of testing regimes for
are straining network capacity and creating “middle ground” distribution level transformer units which are relatively costly to replace,
stresses for ageing assets which were not and which are becoming increasingly critical to network resilience.
designed to deal with dynamic and highly
variable energy flows. The need for a rethink in transformer testing
Furthermore, these challenges are This report seeks to clearly articulate the need for this rethink, to set out what ‘good’ should
being magnified by increasingly stretched look like in transformer testing regimes, which will help networks perform confidently in an
performance expectations from the increasingly challenging environment and explain how advances in technology mean that
energy regulator around service reliability these regimes can now be implemented at scale, without incurring unmanageable cost or
and operational efficiency, as it seeks operational burdens.
to uphold the right of consumers to
expect uninterrupted power supplies at What is the current state of transformer testing in the UK?
an affordable price, notwithstanding the While transformers are typically thought of by asset management leaders as relatively robust
rigours of the energy transition. and low maintenance pieces of equipment, their criticality to power system operations
This daunting operating environment nonetheless means that their health and performance should be carefully monitored.
means it has never been more important for Across the UK, rigorous maintenance regimes are in place to serve transmission level
networks to have an accurate and current transformers which are extremely expensive, tend to be unique in their design and are
picture of the resilience of critical assets therefore hard to replace, and which have very high levels of system dependency riding on
within their infrastructure base, including their performance, says Tony Wills, an applications engineer at Megger.
transformers. But while large transformer But for the vast majority of transformers in place across the UK’s distribution system,
units at high voltage levels have long been Wills says, the picture is very different. “These assets are much smaller, off-the-shelf
stringently monitored and subjected to technologies and historically, the consequences of failure have not been large enough to
rigorous testing regimes, equipment at justify significant expenditure and operational effort on regular testing,” he explains. “It
lower voltage levels – where much of the simply hasn’t been such a big issue when they experience faults. But with decarbonisation
action and stress of decarbonisation is and increasing connections of distributed energy resources at lower voltage levels, that’s set
now manifesting – has historically been to change very rapidly.”
neglected according to experts from test Wills is especially adamant that “middle ground” transformers at distribution level could
equipment and measuring instrument and should now be subjected to more rigorous testing in order to support system reliability
manufacturer, Megger. and resilience and, ultimately, help networks operate more efficiently – an important
The reasons for this are manifold and factor given the downward pressure on operational spending being applied by the energy
not unreasonable. Maintaining extensive regulator.
testing and monitoring for all transformers One key objection to conducting regular testing for distribution level transformers – of
across the distribution network would which there are many and in widely spread locations – has been that many transformer
previously have been unfeasibly costly and tests need to happen “offline”, meaning the asset must be taken out of service to take the
operationally inconvenient for networks, necessary measurements and gauge asset condition.
necessitating increases to planned “It’s therefore been preferable in most scenarios to simply wait for issues to occur, rather
downtime for assets which would have than trying to pre-empt them,” says Wills. However, while some crucial tests will always
knock-on impacts for customers and require offline interventions, there are increasing levels of online testing and monitoring
undermine efficiency. which can be conducted thanks to advances in technology, he points out.

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