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Caring for distribution transformer oils

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A guide to monitoring the performance of your distribution transformers through regular oil checks, and the best esters to use to ensure maximum functionality.

Testing fluid can be vital in order to ensure your transformer continues to perform at its optimum level, while it can also help to pick up any faults before they become too big to repair.

In the case of distribution transformers, there is a clear testing plan you can adopt in order to ensure its continuing functionality. Firstly, you should check the oil before energising, then again after the first year of service and at five year intervals thereafter.


This schedule can of course be adapted to cater for the specific features of your distribution transformer. For example, larger machines such as power transformers may be highly loaded or carry out a critical function. In these cases, it is good to increase the frequency of your test to incorporate regular performance evaluation.

Types of transformer esters

It is recommended that you use a natural or synthetic transformer ester as opposed to the traditional mineral oil. These perform well in all kinds of transformer, and are especially useful for the crucial role played by distribution transformers.

As distribution transformers are often located in or near buildings, the extra safety provided by these transformer oils is hugely significant. For example, in contrast to mineral oils, they have a 100% fire safety record, and their higher moisture tolerance greatly reduces the likelihood of breakdowns.

This in turn results in lower maintenance level requirements, and these esters are also readily biodegradable whereas mineral oils are not. Overall, they can be shown to be the best option.

Further distribution transformer performance analysis

No matter which kind of transformer oil you choose, all can still be tested using traditional Furan and Dissolved Gas Analysis (DGA) methods in order to ensure continuing high performance.

While these processes do check the oil, both are used to check transformer performance rather than oil quality. The tests carried out under these methods can highlight issues early and allow them to be rectified without the need for any major work to be done on your transformer.

By adhering to a set maintenance schedule incorporating tests such as these, you can avoid the potentially dangerous and costly repercussions of transformers developing a fault or breaking down.

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