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The Megger guide to
insulating oil dielectric
breakdown testing
2 www.megger.com The Megger guide to insulating oil dielectric breakdown testing
Contents
1. Introduction .........................................................................................................................3
2. What are the methods for testing oil? ..................................................................................3
3. What is oil dielectric breakdown voltage testing? .................................................................4
4. Who needs to perform dielectric breakdown voltage tests? ..................................................4
5. Which types of insulating oil can be tested? ......................................................................... 4
6. Why, when and how often is oil testing performed? ............................................................6
7. What are the test standards and their differences? ............................................................... 6
7.1 ASTM standards (USA) ............................................................................................... 8
7.2 IEC standards (international) ......................................................................................9
8. How should an oil sample be taken? .................................................................................. 10
9. Preparing the test vessel ..................................................................................................... 12
10. Why measure oil sample temperature? ...............................................................................13
11. How do I know whether my test results are valid? ..............................................................14
12. How do I know if my fluid has passed the test? ..................................................................14
12.1 USA – ASTM and IEEE standards ..............................................................................15
12.2 International IEC standards ......................................................................................15
13. Can new oil fail a dielectric breakdown test? ......................................................................16
14. Can I verify my test instrument performance? ....................................................................17
15. How do oil test sets detect dielectric breakdown? ..............................................................17
15.1 Testing silicone oil ....................................................................................................18
16. Choosing an oil dielectric breakdown voltage test set .........................................................18
16.1 On-site versus laboratory testing .............................................................................. 18
16.2 General instrument selection considerations ............................................................18
16.3 Selection considerations specific to laboratory instruments .......................................24
16.4 Selection considerations specific to portable instruments .........................................25
17. Megger OTS range summary ..............................................................................................27
Acknowledgments
Megger gratefully acknowledges the support of John Noakhes of TJ/H2b Analytical Services for his help in compiling this publication.