Distribution transformers

Keeping a close eye on distribution transformers

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Bas Verhoeven Bas Verhoeven
Director Marketing & Sales KEMA Laboratories

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KEMA Laboratories
Transformer prepairing for testing
Distribution transformers are today seen by some as commodity items. But this is a dangerous misconception. These highly specialised components occupy a crucial position in the grid. Hence it is vital to properly consider their performance and reliability throughout specification, manufacturing and tendering. Our experience in testing bears this out: 1 in 4 distribution transformers initially fail type testing.
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  • Keywords: KEMA Laboratories, Corporate energy users, Manufacturers, Utilities

KEMA Laboratories has supported the T&D industry for many decades through renowned independent testing and certification of grid components. By analysing the results of these tests, we can also provide component manufacturers and their customers with valuable insights to help them deliver a safer, more reliable energy supply.

For example, a recent analysis of ten years of data from type tests for distribution transformers showed that initial failure rates remain as high as ever at around 25%. Looking a little deeper, we analysed the results of some 250 distribution transformer short-circuit tests performed over a five-year period (see figure 1). The transformers had rated powers ranging from 50 to 5000 kVA, with a maximum primary voltage of 13.8 kV. 202 of these transformers were certified while 48 weren’t. Given the grave consequences that would result from a transformer failing in operation rather than our test bays, these figures represent a significant risk to grid reliability.

The threat is further highlighted by looking at dry-type (cast resin) transformers. IEC 60076-11 defines special tests for climatic (C), environmental (E) and fire behaviour (F). Since 2008, we have tested 47 dry-type transformers for C, E and/or F class verifications. The results show an initial failure rate of more than 60% for combined testing (figure 2). Especially worrying is the 50% failure rate for fire behaviour. Cast-resin transformers are often used in buildings so poor fire behaviour directly threatens lives. This is a particular issue for places such as the Middle East where high loads (e.g. due to demand for air conditioning) and extreme ambient temperatures put transformers under greater strain and risk of fire.

World renowned service
The test data proves that distribution transformers cannot be seen as commodity goods, and instead require proper attention to make sure they function as intended. The most reliable way to prove the quality of a component is through independent, physical type testing. This is where KEMA Laboratories comes in. Our industry-leading facilities, skilled test engineers and global reputation for excellence ensure all stakeholders can have full confidence in a KEMA-certified component.

We offer a full range of testing and certification services for distributor transformers. This includes going beyond the standards to customise tests for local conditions or specific user requirements. For example, we can perform tests at high ambient temperatures of 50 °C or more, allowing manufacturers to demonstrate that their transformers are up to the rigours of extreme climates.

Be there when you can’t be there
At KEMA Laboratories, we see ourselves as a partner to the T&D industry. Hence we are continually looking to tailor our services to meet the evolving challenges and financial pressures faced by our customers and their customers. Our excellent logistics, multiple flexible test bays and ability to schedule tests in the most efficient way possible mean we can minimise total testing time – especially for batches of transformers.

Manufacturers can also choose to witness testing – either in person at one of our facilities or remotely via the internet. Both options allow manufacturers and their customers to be actively involved in the testing process. For remote witnessing, tests can be followed through a live web cam in the test bay and full interaction with the test engineers is possible via video conference. Screen sharing enables a direct evaluation of the results. What’s more, because we operate multiple testing shifts each day, we can schedule tests to be convenient for the witnesses’ time zone.

As they require little or no assembly or mounting, distributor transformers are well suited to remote witnessing of tests. By offering the choice of in-person or remote witnessing, we aim to give distribution transformers manufacturers and their customers maximum flexibility in how they do business – while delivering complete confidence in these highly important components.

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