ET online
January 2009
How to assess the condition of a transformer relatively quickly

How to assess the condition of a transformer relatively quickly

01 January 2009

Matz Öhlén M.Sc., E.E. - Marketing and sales manager

There is a technique called frequency response analysis (FRA). FRA is like a whole body scan of a transformer. It looks at the transformer as a single system.

A variable frequency is applied to the transformer resulting in a trace, showing how the transformer reacted to the frequencies applied. This is the transformer's 'fingerprint'.

This 'fingerprint' can be compared to a previously measured 'fingerprint' trace. If the traces are the same, then nothing within the transformer has changed, the transformer is as healthy as it was and can be safely reconnected to the system.

If a difference is seen then there may be a problem with the transformer and further investigation would be required utilising some of the other available test methods to pinpoint the problem.

FRA is a fast (1 hr) test giving a picture of the health of the transformer as a whole. If there are no changes you can reconnect the transformer quickly, saving time and money. It does however require a reference trace. Ideally, FRA would be performed as part of the commissioning of the transformer to gain the reference trace.

Most in service transformers were commissioned many years ago but running the test today, as part of planned maintenance procedures is an alternative way to gain a reference trace,providing the transformer is functioning in a satisfactory manner. These traces should then be retained along with the connection conditions of the transformer for future comparison.

The FRAX101 Frequency Response Analyser complies with most common operating standard at 10 V, although it can test at lower voltages if previous tests had been done at a non- standard voltage. It has the highest frequency response and can sweep either from low frequency to high, or in the reverse direction, depending on what was done in the original finger-printing.

And of course as these outages rarely occur on pleasant summer's days, FRAX can be left connected to the transformer while you retire out of the weather to operate the unit and collect the data on your computer using Bluetooth® protocols.

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