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OTS80PB and OTS60PB OTS100AF, OTS80AF and OTS60AF
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Preparations for use
7.4. Test vessel preparation
When unexpected results are experienced in testing the dielectric breakdown of oil samples the cause can often be
traced to insufficient attention to one or more of the following key elements of vessel preparation:
1. Storing and subsequent cleaning
2. Setting the electrode Gap
3. Ensuring thorough rinsing of the test vessel and then immediately filling the vessel with the oil sample to be tested.
4. Exclusion of all air from contact with the oil sample and prevention of air/ moisture contamination; (particularly
relevant when using an impeller to stir the insulating oil sample).
5. Selecting the optimum stirring option for the insulating oil sample and test standard required.
Any of these elements have the potential to cause an un-expected drop in breakdown voltage level. Therefore it should
be verified that each aspect has been properly considered and implemented.
Taking each of these elements in turn:-
Storing and subsequent cleaning
IEC
Fig 1: IEC Storing oil samples
IEC 60156 recommends that a separate test vessel assembly is used
for each type of insulating fluid that is to be tested. The standard
requires that the test vessels are filled with dry insulating fluid of the
appropriate type, then covered and stored in a dry place.
ASTM
Fig 2: ASTM Storing oil samples
ASTM offers an alternative option of storing the vessels empty in
dustfree cabinet.
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