About Dielectric Breakdown / Oil Tester
In the world of electrical engineering and power distribution, ensuring the reliability and safety of equipment is paramount. One critical aspect of this maintenance program is testing the dielectric strength of insulating oils, used in transformers, switchgear and other electrical apparatus.
Dielectric breakdown oil testers play a vital role in this process, helping to prevent costly downtime, equipment failures, and electrical fires; proper maintenance is essential to ensure that the dielectric strength of the oil does not deteriorate.
Why Should Dielectric Breakdown Oil Tests Be Part Of Your Maintenance Program?
For in-service equipment in particular, there are many testing techniques used to evaluate the condition of the insulating oil. If the technique of dissolved gas analysis is excluded, oil tests can be divided into two basic groups.
Group 1: Tests to evaluate the immediate condition and acceptability of the insulation oil - the chosen method is the Karl Fischer (KF) method and testing capabilities include dielectric breakdown, moisture content and measurement of the dielectric dissipation factor.
Group 2: Tests to evaluate the degree of degradation and aging of the equipment’s insulation system. These tests include interfacial tension, acidity (neutralisation value), resistivity and visual determination of colour and appearance of the insulating oil. The darker the colour the more contaminants it presents.
While all of these tests are useful in particular circumstances, the most convenient and most universally applicable is dielectric breakdown voltage testing.
Who needs to perform dielectric breakdown voltage tests?
There are many types of organisation that benefit from carrying out tests on transformer oil. These include:
- Utility contractors (principally in substations)
- Utility companies (principally in power stations)
- Rail companies (locomotive HV step-down transformers and switchgear)
- Oil test laboratories (providing testing services)
- Transformer and switchgear manufacturers (quality control of oil)
- Oil companies (testing new oil during manufacture)
Which types of insulating oil can be tested?
While the generic term ‘oil’ is almost universally used to describe insulating fluids, there are currently five different types of insulating fluid in common use. These are:
- Mineral oil
- High molecular weight hydrocarbon (HMWH) fluids
- Silicone fluids
- Synthetic ester fluids
- Natural ester (vegetable oil) fluids
All of these oil types can be tested for dielectric breakdown voltage and tested with Megger OTS range test sets.
Why and when should you conduct dielectric breakdown testing?
The dielectric breakdown voltage test is a relatively quick and easy way of determining the amount of insulating oil contaminant. Usually the contaminant is water, but it can also be conductive particles, dirt, debris, insulating particles and the by-products of oxidation and aging of the oil.
For in-service equipment, the dielectric breakdown voltage test offers a useful and convenient way to detect moisture and other contamination in the oil before it leads to a catastrophic failure. The information gained from the test can also be used as an aid to:
- Predicting the remaining life of a transformer
- Enhancing operational safety
- Preventing equipment fires
- Maintaining reliability
Dielectric breakdown voltage testing is also carried out on new oil before it is used to fill equipment, and as part of the acceptance testing for deliveries of new and reprocessed oil.
How often should you conduct dielectric breakdown testing?
Dielectric breakdown voltage testing is an important element in the maintenance programme of any item of oil insulated electrical equipment. However, to get the maximum benefit from this type of testing, Megger strongly recommends that the oil is tested at least once a year and preferably twice a year. The results should be recorded, as trending the data will make it easier to identify sudden or unexpected changes. If a sudden change in the results is found, the transformer can be inspected for leaks; the oil level can be checked and the water content of the oil evaluated. If contamination is confirmed, it will often be possible to dry and filter the oil, thereby reconditioning it rather than having to replace it with expensive new oil.
If you have any questions contact our friendly team today - experts are here to advise on the full range of dielectric breakdown / oil testers.