Electrical Tester online
March 2009
When moisture means trouble!

When moisture means trouble!

02 March 2009

Adrian Parker - Applications engineer

Moisture in insulating oil not only reduces the efficiency of the oil as an insulator but may also indicate the degradation of solid insulation in transformers and switchgear, since water is a by-product of the breakdown of this type of insulation. The ability to accurately measure the moisture content of oil is, therefore, highly desirable.

One of the most convenient and dependable solutions is the use of Karl Fischer coulometric titrimetry. This is the recognised industry standard method for determining moisture content, and the standard against which other instruments are calibrated.

The Karl Fischer method is very sensitive, which is important as most insulating oils can be expected to have a moisture content in the low mg/Kg (parts per million) range. The method can however be used over a much wider range should this prove necessary.

Modern test sets based on the Karl Fischer method, such as those in Megger’s KF range, are straightforward in operation, allowing them to be used easily by non-laboratory personnel, and they can provide accurate results in under a minute.

With integral batteries and rugged construction, KF test sets have been specifically designed to be as suitable for use on site as in the workshop and laboratory. This is an important benefit, as on-site testing eliminates the contamination risks and other problems associated with storing and transporting samples, as well as giving on-the-spot results, thus allowing equipment with defective oil to be taken out of service without delay.

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